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class="menu navigation"><div class="list-h"><a target="_blank" rel="external nofollow noopener noreferrer" href="https://github.com/MHuiG" active-action="action-https:githubcomMHuiG"><i class="fa-brands fa-github color-github fa-fw"></i><p>Github</p></a><a href="/pages/friends/" active-action="action-pagesfriends"><i class="fa-duotone fa-link color-friends fa-fw"></i><p>友链</p></a><a href="/pages/about/" active-action="action-pagesabout"><i class="fa-duotone fa-user-tie color-about fa-fw"></i><p>关于</p></a><a href="https://www.travellings.cn/go-by-clouds.html" target="_blank" active-action="action-https:wwwtravellingscngo-by-cloudshtml" rel="external nofollow noopener noreferrer"><i class="fa-duotone fa-subway color-travellings fa-fw"></i><p>Travelling</p></a></div></div></div></div><div id="scroll-down" style="display:none"><i class="fa fa-chevron-down scroll-down-effects"></i></div></div></div><div id="safearea"><div class="body-wrapper"><div id="l_main" class><article itemscope itemtype="http://schema.org/Article" class="article post white-box reveal md shadow floatable blur article-type-docs" id="docs" itemprop="blogPost"><link itemprop="mainEntityOfPage" href="https://blog.mhuig.top/notes/datacom/6"><span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="MHuiG"></span><span hidden itemprop="post" itemscope itemtype="http://schema.org/Post"><meta itemprop="name" content="MHuiG"><meta itemprop="description" content="MHuiG&#39;s Blog (MHuiG的博客) MHuiG&#39;s Neverland（MHuiG的梦幻岛） —— MHuiG(@MHuiG) 随便写写画画的地方 - 技术博客"></span><span hidden><meta itemprop="image" content="/lib/favicon/android-chrome-192x192.png"></span><div class="article-meta" id="top"><span hidden itemprop="name headline"></span></div><div id="layoutHelper-page-plugins"></div><div id="post-body" itemprop="articleBody"><p> <span class="p logo center large">IP 编址</span></p><br><h1 hidden>IP 编址</h1><div class="story post-story"><h2 id="IP"><a href="#IP" class="headerlink" title="IP"></a>IP</h2><p><code>IP</code>: 网际协议，网络层协议，用来为网络中设备分配逻辑地址.</p><p>网络层的逻辑地址就是 IP 地址，IP 地址是可以更改的，当设备在不同网络中，根据所处网络的不同发生变化，在同一个网络内必须保证唯一性。设备有了 IP 地址后，就可以在网络中进行通信.</p></div><div class="story post-story"><h2 id="IP报文头部"><a href="#IP报文头部" class="headerlink" title="IP报文头部"></a>IP 报文头部</h2><p><a target="_blank" rel="external nofollow noopener noreferrer" href="https://www.rfc-editor.org/rfc/rfc791.txt">RFC 791</a></p><figure class="highlight plaintext"><table><tbody><tr><td class="code"><pre><span class="line">0 1 2 3 </span><br><span class="line">0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 </span><br><span class="line">+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</span><br><span class="line">|Version| IHL |Type of Service| Total Length |</span><br><span class="line">+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</span><br><span class="line">| Identification |Flags| Fragment Offset |</span><br><span class="line">+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</span><br><span class="line">| Time to Live | Protocol | Header Checksum |</span><br><span class="line">+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</span><br><span class="line">| Source Address |</span><br><span class="line">+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</span><br><span class="line">| Destination Address |</span><br><span class="line">+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</span><br><span class="line">| Options | Padding |</span><br><span class="line">+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</span><br><span class="line"></span><br><span class="line"> Example Internet Datagram Header</span><br></pre></td></tr></tbody></table></figure><p><img src="https://static.mhuig.top/npm/mhgoos@0.0.1701856320515/image-20231206174344057.png" class="lazyload" data-srcset="https://static.mhuig.top/npm/mhgoos@0.0.1701856320515/image-20231206174344057.png" srcset="data:image/gif;base64,R0lGODlhAQABAIAAAP///////yH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==" alt="IP报文头部"></p><h3 id="基本信息行"><a href="#基本信息行" class="headerlink" title="基本信息行"></a>基本信息行</h3><p><code>Version</code>: 版本，<code>4bit</code>, 用来标明当前 IP 协议的版本，如果当前报文在 IPv4 时，则该字段的值为 <code>4(0b0100)</code></p><p><code>IHL</code>: IP 头部长度，<code>4bit</code>, 范围 <code>20-60</code> 字节，每个单位代表 <code>4</code> 字节</p><p><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.186ex" xmlns="http://www.w3.org/2000/svg" width="11.906ex" height="1.756ex" role="img" focusable="false" viewBox="0 -694 5262.6 776"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mn"><path data-c="30" d="M96 585Q152 666 249 666 297 666 345 640T423 548Q460 465 460 320 460 165 417 83 397 41 362 16T301-15 250-22Q224-22 198-16T137 16 82 83Q39 165 39 320 39 494 96 585ZM321 597Q291 629 250 629 208 629 178 597 153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16 290 16 318 46 347 76 354 130T362 333Q362 478 354 524T321 597Z"/></g><g data-mml-node="mi" transform="translate(500,0)"><path data-c="1D44F" d="M73 647Q73 657 77 670T89 683Q90 683 161 688T234 694Q246 694 246 685T212 542Q204 508 195 472T180 418L176 399Q176 396 182 402 231 442 283 442 345 442 383 396T422 280Q422 169 343 79T173-11Q123-11 82 27T40 150V159Q40 180 48 217T97 414Q147 611 147 623T109 637Q104 637 101 637H96Q86 637 83 637T76 640 73 647ZM336 325V331Q336 405 275 405 258 405 240 397T207 376 181 352 163 330L157 322 136 236Q114 150 114 114 114 66 138 42 154 26 178 26 211 26 245 58 270 81 285 114T318 219Q336 291 336 325Z"/></g><g data-mml-node="mn" transform="translate(929,0)"><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z"/><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z" transform="translate(500,0)"/><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z" transform="translate(1000,0)"/><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z" transform="translate(1500,0)"/></g><g data-mml-node="mo" transform="translate(3206.8,0)"><path data-c="3D" d="M56 347Q56 360 70 367H707Q722 359 722 347 722 336 708 328L390 327H72Q56 332 56 347ZM56 153Q56 168 72 173H708Q722 163 722 153 722 140 707 133H70Q56 140 56 153Z"/></g><g data-mml-node="mn" transform="translate(4262.6,0)"><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z"/><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z" transform="translate(500,0)"/></g></g></g></svg></mjx-container> ,<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.05ex" xmlns="http://www.w3.org/2000/svg" width="6.159ex" height="1.581ex" role="img" focusable="false" viewBox="0 -677 2722.4 699"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mn"><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z"/><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z" transform="translate(500,0)"/></g><g data-mml-node="mo" transform="translate(1222.2,0)"><path data-c="D7" d="M630 29Q630 9 609 9 604 9 587 25T493 118L389 222 284 117Q178 13 175 11 171 9 168 9 160 9 154 15T147 29Q147 36 161 51T255 146L359 250 255 354Q174 435 161 449T147 471Q147 480 153 485T168 490Q173 490 175 489 178 487 284 383L389 278 493 382Q570 459 587 475T609 491Q630 491 630 471 630 464 620 453T522 355L418 250 522 145Q606 61 618 48T630 29Z"/></g><g data-mml-node="mn" transform="translate(2222.4,0)"><path data-c="34" d="M462 0Q444 3 333 3 217 3 199 0H190V46H221Q241 46 248 46T265 48 279 53 286 61Q287 63 287 115V165H28V211L179 442Q332 674 334 675 336 677 355 677H373L379 671V211H471V165H379V114Q379 73 379 66T385 54Q393 47 442 46H471V0H462ZM293 211V545L74 212 183 211H293Z"/></g></g></g></svg></mjx-container> 字节<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.186ex" xmlns="http://www.w3.org/2000/svg" width="4.651ex" height="1.692ex" role="img" focusable="false" viewBox="0 -666 2055.8 748"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mo"><path data-c="3D" d="M56 347Q56 360 70 367H707Q722 359 722 347 722 336 708 328L390 327H72Q56 332 56 347ZM56 153Q56 168 72 173H708Q722 163 722 153 722 140 707 133H70Q56 140 56 153Z"/></g><g data-mml-node="mn" transform="translate(1055.8,0)"><path data-c="36" d="M42 313Q42 476 123 571T303 666Q372 666 402 630T432 550Q432 525 418 510T379 495Q356 495 341 509T326 548Q326 592 373 601 351 623 311 626 240 626 194 566 147 500 147 364L148 360Q153 366 156 373 197 433 263 433H267Q313 433 348 414 372 400 396 374T435 317Q456 268 456 210V192Q456 169 451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z"/><path data-c="30" d="M96 585Q152 666 249 666 297 666 345 640T423 548Q460 465 460 320 460 165 417 83 397 41 362 16T301-15 250-22Q224-22 198-16T137 16 82 83Q39 165 39 320 39 494 96 585ZM321 597Q291 629 250 629 208 629 178 597 153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16 290 16 318 46 347 76 354 130T362 333Q362 478 354 524T321 597Z" transform="translate(500,0)"/></g></g></g></svg></mjx-container> 字节</p><p><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.186ex" xmlns="http://www.w3.org/2000/svg" width="10.775ex" height="1.756ex" role="img" focusable="false" viewBox="0 -694 4762.6 776"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mn"><path data-c="30" d="M96 585Q152 666 249 666 297 666 345 640T423 548Q460 465 460 320 460 165 417 83 397 41 362 16T301-15 250-22Q224-22 198-16T137 16 82 83Q39 165 39 320 39 494 96 585ZM321 597Q291 629 250 629 208 629 178 597 153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16 290 16 318 46 347 76 354 130T362 333Q362 478 354 524T321 597Z"/></g><g data-mml-node="mi" transform="translate(500,0)"><path data-c="1D44F" d="M73 647Q73 657 77 670T89 683Q90 683 161 688T234 694Q246 694 246 685T212 542Q204 508 195 472T180 418L176 399Q176 396 182 402 231 442 283 442 345 442 383 396T422 280Q422 169 343 79T173-11Q123-11 82 27T40 150V159Q40 180 48 217T97 414Q147 611 147 623T109 637Q104 637 101 637H96Q86 637 83 637T76 640 73 647ZM336 325V331Q336 405 275 405 258 405 240 397T207 376 181 352 163 330L157 322 136 236Q114 150 114 114 114 66 138 42 154 26 178 26 211 26 245 58 270 81 285 114T318 219Q336 291 336 325Z"/></g><g data-mml-node="mn" transform="translate(929,0)"><path data-c="30" d="M96 585Q152 666 249 666 297 666 345 640T423 548Q460 465 460 320 460 165 417 83 397 41 362 16T301-15 250-22Q224-22 198-16T137 16 82 83Q39 165 39 320 39 494 96 585ZM321 597Q291 629 250 629 208 629 178 597 153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16 290 16 318 46 347 76 354 130T362 333Q362 478 354 524T321 597Z"/><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z" transform="translate(500,0)"/><path data-c="30" d="M96 585Q152 666 249 666 297 666 345 640T423 548Q460 465 460 320 460 165 417 83 397 41 362 16T301-15 250-22Q224-22 198-16T137 16 82 83Q39 165 39 320 39 494 96 585ZM321 597Q291 629 250 629 208 629 178 597 153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16 290 16 318 46 347 76 354 130T362 333Q362 478 354 524T321 597Z" transform="translate(1000,0)"/><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z" transform="translate(1500,0)"/></g><g data-mml-node="mo" transform="translate(3206.8,0)"><path data-c="3D" d="M56 347Q56 360 70 367H707Q722 359 722 347 722 336 708 328L390 327H72Q56 332 56 347ZM56 153Q56 168 72 173H708Q722 163 722 153 722 140 707 133H70Q56 140 56 153Z"/></g><g data-mml-node="mn" transform="translate(4262.6,0)"><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z"/></g></g></g></svg></mjx-container> ,<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.05ex" xmlns="http://www.w3.org/2000/svg" width="5.028ex" height="1.581ex" role="img" focusable="false" viewBox="0 -677 2222.4 699"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mn"><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z"/></g><g data-mml-node="mo" transform="translate(722.2,0)"><path data-c="D7" d="M630 29Q630 9 609 9 604 9 587 25T493 118L389 222 284 117Q178 13 175 11 171 9 168 9 160 9 154 15T147 29Q147 36 161 51T255 146L359 250 255 354Q174 435 161 449T147 471Q147 480 153 485T168 490Q173 490 175 489 178 487 284 383L389 278 493 382Q570 459 587 475T609 491Q630 491 630 471 630 464 620 453T522 355L418 250 522 145Q606 61 618 48T630 29Z"/></g><g data-mml-node="mn" transform="translate(1722.4,0)"><path data-c="34" d="M462 0Q444 3 333 3 217 3 199 0H190V46H221Q241 46 248 46T265 48 279 53 286 61Q287 63 287 115V165H28V211L179 442Q332 674 334 675 336 677 355 677H373L379 671V211H471V165H379V114Q379 73 379 66T385 54Q393 47 442 46H471V0H462ZM293 211V545L74 212 183 211H293Z"/></g></g></g></svg></mjx-container> 字节<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.186ex" xmlns="http://www.w3.org/2000/svg" width="4.651ex" height="1.692ex" role="img" focusable="false" viewBox="0 -666 2055.8 748"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mo"><path data-c="3D" d="M56 347Q56 360 70 367H707Q722 359 722 347 722 336 708 328L390 327H72Q56 332 56 347ZM56 153Q56 168 72 173H708Q722 163 722 153 722 140 707 133H70Q56 140 56 153Z"/></g><g data-mml-node="mn" transform="translate(1055.8,0)"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/><path data-c="30" d="M96 585Q152 666 249 666 297 666 345 640T423 548Q460 465 460 320 460 165 417 83 397 41 362 16T301-15 250-22Q224-22 198-16T137 16 82 83Q39 165 39 320 39 494 96 585ZM321 597Q291 629 250 629 208 629 178 597 153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16 290 16 318 46 347 76 354 130T362 333Q362 478 354 524T321 597Z" transform="translate(500,0)"/></g></g></g></svg></mjx-container> 字节</p><p>字节长度取值一定是四的倍数.</p><p><code>DS/TOS</code>: 差分服务域，服务类别，<code>8bit</code>, 让特定的数据拥有更高的优先级.</p><p><code>Total length</code>: 数据包总长度，<code>16bit</code>, 用于标识 IP 报文头部加数据载荷的长度，最大 <code>65535</code> 字节.</p><h3 id="分片行"><a href="#分片行" class="headerlink" title="分片行"></a>分片行</h3><p>[<code>MTU</code>: 最大传输单元，用于限制报文不被分片的最大字节，默认情况下 <code>MTU</code> 值为 <code>1500</code> 字节.]</p><p><code>ID</code>: 标识，<code>16bit</code>, 用于顺序 IP 报文，同一个报文得到的分片信息中的 ID 相同.</p><p><code>Flages</code>: 标志位，<code>3bit</code>.</p><ul><li>最高位被保留，固定为 <code>0</code>.</li><li> 中间位为 <code>DF</code> 位：如果置位为 <code>1</code>, 则表示该报文不能被分片.</li><li> 最低位称为 <code>more</code> 位：如果置位 <code>1</code>, 则表示后续还有分片报文.</li></ul><p>如果报文大于 MTU 值并且 DF 置位，直接丢弃.</p><p><code>Offset</code>: <code>13bit</code>, 片偏移，用于标识分片包在原始报文的位置.</p><p>片偏移指出：较长的分组在分片后，某片在原分组中的相对位置。也就是说，相对于用户数据字段的起点，该片从何处开始。片偏移以 8 个字节为偏移单位。这就是说，每个分片的长度一定是 8 字节 (64 位) 的整数倍.</p><p>【例】一数据报的总长度为 3820 字节，其数据部分为 3800 字节长 (使用固定自部)，需要分片为长度不超过 1420 字节的数据报片。因固定首部长度为 20 字节，因此每个数据报片的数据部分长度不能超过 1400 字节。于是分为 3 个数据报片，具数据部分的长度分别为 1400 ，1400 和 1000 字节。原始数据报首部被复制为各数据报片的首部，但必须修以有关字段的值。下面给出分片后得出的结果 (请注意片偏移的数值)。</p><table><thead><tr><th>数据报</th><th>总长度</th><th>标识</th><th> MF</th><th>DF</th><th> 片偏移</th></tr></thead><tbody><tr><td>原始数据报</td><td> 3820</td><td>12345</td><td>0</td><td>0</td><td>0(0/8=0)</td></tr><tr><td> 数据报片 1</td><td>1420</td><td>12345</td><td>1</td><td>0</td><td>0(0/8=0)</td></tr><tr><td> 数据报片 2</td><td>1420</td><td>12345</td><td>1</td><td>0</td><td>175(1400/8=175)</td></tr><tr><td> 数据报片 3</td><td>1020</td><td>12345</td><td>0</td><td>0</td><td>350(2800/8=350)</td></tr></tbody></table><p>现在假定数据报片 2 经过某个网络时还需要再进行分片，即划分为数据报片 2-1 (携带数据 800 字节) 和数据报片 2-2 (携带数据 600 字节)。那么这两个数据报片的总长度、标识、MF、DF 和片偏移分别为: 820,12345,1,0,175; 620,12345,1,0,275。</p><h3 id="功能行"><a href="#功能行" class="headerlink" title="功能行"></a>功能行</h3><p><code>TTL</code>: 生存周期，<code>8bit</code>, 用来在 IP 报文转发过程中，打破环路对网络的影响，最大值 <code>255</code>, 会在数据包经过一次第三层转发时减 <code>1</code>. 当值为 <code>0</code> 时数据包被丢弃.</p><p><code>Protocol</code>: <code>8bit</code>, 用于标明网络层处理完 IP 报文后，需要交给上层的某个协议继续处理.</p><ul><li><code>1</code>: <code>ICMP</code></li><li><code>6</code>: <code>TCP</code></li><li><code>17</code>: <code>UDP</code></li></ul><p><code>Header Checksum</code>: <code>16bit</code>, 首部校验和，检测 IP 首部是否发生错误.</p><h3 id="地址行"><a href="#地址行" class="headerlink" title="地址行"></a>地址行</h3><p><code>SIP</code>: 源 IP 地址，<code>32bit</code>, 表明当前数据包从哪出发.</p><p><code>DIP</code>: 目的 IP 地址，<code>32bit</code>, 表明当前数据包去往何处.</p><h3 id="可选项"><a href="#可选项" class="headerlink" title="可选项"></a>可选项</h3><p><code>Options</code>: 可选项，可变长度，最大 <code>40</code> 字节。军事或研究方向，支持松散源路由，严格源路由等等.</p></div><div class="story post-story"><h2 id="IP地址"><a href="#IP地址" class="headerlink" title="IP地址"></a>IP 地址</h2><p>IP 地址：用来标识网络中的一个节点或网络设备的接口，总长度 <code>32bit</code>, 约 42.9 亿 (<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:0" xmlns="http://www.w3.org/2000/svg" width="2.919ex" height="1.887ex" role="img" focusable="false" viewBox="0 -833.9 1290.1 833.9"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="TeXAtom" transform="translate(533,363) scale(0.707)" data-mjx-texclass="ORD"><g data-mml-node="mn"><path data-c="33" d="M127 463Q100 463 85 480T69 524Q69 579 117 622T233 665Q268 665 277 664 351 652 390 611T430 522Q430 470 396 421T302 350L299 348Q299 347 308 345T337 336 375 315Q457 262 457 175 457 96 395 37T238-22Q158-22 100 21T42 130Q42 158 60 175T105 193Q133 193 151 175T169 130Q169 119 166 110T159 94 148 82 136 74 126 70 118 67L114 66Q165 21 238 21 293 21 321 74 338 107 338 175V195Q338 290 274 322 259 328 213 329L171 330 168 332Q166 335 166 348 166 366 174 366 202 366 232 371 266 376 294 413T322 525V533Q322 590 287 612 265 626 240 626 208 626 181 615T143 592 132 580H135Q138 579 143 578T153 573 165 566 175 555 183 540 186 520Q186 498 172 481T127 463Z"/><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z" transform="translate(500,0)"/></g></g></g></g></g></svg></mjx-container>), 每个 IP 地址都由网络位和主机位组成.</p><p>网络位：用来标明当前设备的网络位置.</p><p>主机位：用来标明当前主机在当前网络中的位置.</p><p>网络掩码: 32bit, 由连续的 1 和 0 构成，其中 1 标记的是网络位，0 标记的是主机位.</p><p>网络地址：当主机位全都为 0 时，表示当前网络信息.</p><p>广播地址：当主机位全都为 1 时，表示当前网络范围内的广播地址.</p><p>可用地址：可分配给网络中的节点或网络设备接口的地址.</p><p>一个网络内的可用 IP 地址<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.186ex" xmlns="http://www.w3.org/2000/svg" width="8.526ex" height="2.117ex" role="img" focusable="false" viewBox="0 -853.7 3768.5 935.7"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mo"><path data-c="3D" d="M56 347Q56 360 70 367H707Q722 359 722 347 722 336 708 328L390 327H72Q56 332 56 347ZM56 153Q56 168 72 173H708Q722 163 722 153 722 140 707 133H70Q56 140 56 153Z"/></g><g data-mml-node="msup" transform="translate(1055.8,0)"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mi" transform="translate(533,363) scale(0.707)"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g></g><g data-mml-node="mo" transform="translate(2268.3,0)"><path data-c="2212" d="M84 237T84 250 98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z"/></g><g data-mml-node="mn" transform="translate(3268.5,0)"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g></g></g></svg></mjx-container> ,<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.025ex" xmlns="http://www.w3.org/2000/svg" width="1.303ex" height="1.595ex" role="img" focusable="false" viewBox="0 -694 576 705"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mi"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g></g></g></svg></mjx-container>表示主机位的位数.</p><p>网络地址和广播地址不能直接被节点或网络设备所使用.</p><h3 id="IP地址分类"><a href="#IP地址分类" class="headerlink" title="IP地址分类"></a>IP 地址分类</h3><h4 id="有类IP地址"><a href="#有类IP地址" class="headerlink" title="有类IP地址"></a>有类 IP 地址</h4><p><code>A</code>: 第一个 bit 为 <code>0</code>, 并且掩码长度为 <code>8</code>.</p><p><code>(0.0.0.0-127.255.255.255)</code></p><p><code>B</code>: 前两个 bit 为 <code>10</code>, 并且掩码长度为 <code>16</code>.</p><p><code>(128.0.0.0-191.255.255.255)</code></p><p><code>C</code>: 前三个 bit 为 <code>110</code>, 并且掩码长度为 <code>24</code>.</p><p><code>(192.0.0.0-223.255.255.255)</code></p><p><code>D</code>: 前四个 bit 为 <code>1110</code>, 组播地址.</p><p><code>(224.0.0.0-239.255.255.255)</code></p><p><code>E</code>: 前四个 bit 为 <code>1111</code>.</p><p><code>(240.0.0.0-255.255.255.255)</code></p><h4 id="按照使用范围分类"><a href="#按照使用范围分类" class="headerlink" title="按照使用范围分类"></a>按照使用范围分类</h4><p>公有地址：可以在公网范围内使用的地址.</p><p>私有地址：可以在局域网中使用，在不同的局域网中可以重复使用，不能够被公网转发.</p><p>私有地址范围:</p><p><code>A</code>: <code>10.0.0.0-10.255.255.255</code> ; <code>10.0.0.0/8</code></p><p><code>B</code>: <code>172.16.0.0-172.31.255.255</code> ; <code>172.16.0.0/12</code></p><p><code>C</code>: <code>192.168.0.0-192.168.255.255</code> ; <code>192.168.0.0/16</code></p><p>IPv6 私有地址范围:</p><p><code>fc00::/7</code> (ULAs，Unique Local Addresses)</p><h3 id="特殊地址"><a href="#特殊地址" class="headerlink" title="特殊地址"></a>特殊地址</h3><p>这类 IP 地址不能够给设备使用，并且全部具有特定意义.</p><p><code>0.0.0.0</code>: 当设备初次进入网络时，会使用该地址。特定场景下可以代表所有地址.</p><p><code>255.255.255.255</code>: 全网广播地址，可以向广播域内所有设备发送数据.</p><p><code>127.0.0.0-127.255.255.255</code>: 本地环回测试地址，检查本地网卡驱动是否正常.</p></div><div class="story post-story"><h2 id="进制转换"><a href="#进制转换" class="headerlink" title="进制转换"></a>进制转换</h2><h3 id="十进制转二进制"><a href="#十进制转二进制" class="headerlink" title="十进制转二进制"></a>十进制转二进制</h3><p>短除法 倒着写:</p><figure class="highlight plaintext"><table><tbody><tr><td class="code"><pre><span class="line">2|192 0</span><br><span class="line"> ----</span><br><span class="line"> 2|96 0</span><br><span class="line"> ---</span><br><span class="line"> 2|48 0</span><br><span class="line"> ---</span><br><span class="line"> 2|24 0</span><br><span class="line"> ---</span><br><span class="line"> 2|12 0</span><br><span class="line"> ---</span><br><span class="line"> 2|6 0</span><br><span class="line"> ---</span><br><span class="line"> 2|3 1</span><br><span class="line"> --</span><br><span class="line"> 1</span><br><span class="line"></span><br><span class="line">2|168 0</span><br><span class="line"> ----</span><br><span class="line"> 2|84 0</span><br><span class="line"> ---</span><br><span class="line"> 2|42 0</span><br><span class="line"> ---</span><br><span class="line"> 2|21 1</span><br><span class="line"> ---</span><br><span class="line"> 2|10 0</span><br><span class="line"> ---</span><br><span class="line"> 2|5 1</span><br><span class="line"> ---</span><br><span class="line"> 2|2 0</span><br><span class="line"> --</span><br><span class="line"> 1</span><br></pre></td></tr></tbody></table></figure><p>权重减法:</p><figure class="highlight plaintext"><table><tbody><tr><td class="code"><pre><span class="line">192-128=64</span><br><span class="line">64-64=0</span><br><span class="line">1100 0000</span><br><span class="line"></span><br><span class="line">168-128=40</span><br><span class="line">40-32=8</span><br><span class="line">8-8=0</span><br><span class="line">1010 1000</span><br></pre></td></tr></tbody></table></figure><h3 id="二进制转十进制"><a href="#二进制转十进制" class="headerlink" title="二进制转十进制"></a>二进制转十进制</h3><p><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.05ex" xmlns="http://www.w3.org/2000/svg" width="6.627ex" height="1.62ex" role="img" focusable="false" viewBox="0 -694 2929 716"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g 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451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z"/></g></g></g></g></svg></mjx-container></th><th><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:0" xmlns="http://www.w3.org/2000/svg" width="2.119ex" height="1.887ex" role="img" focusable="false" viewBox="0 -833.9 936.6 833.9"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mn" transform="translate(533,363) scale(0.707)"><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z"/></g></g></g></g></svg></mjx-container></th><th><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:0" xmlns="http://www.w3.org/2000/svg" width="2.119ex" height="1.904ex" role="img" focusable="false" viewBox="0 -841.7 936.6 841.7"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mn" transform="translate(533,363) scale(0.707)"><path data-c="34" d="M462 0Q444 3 333 3 217 3 199 0H190V46H221Q241 46 248 46T265 48 279 53 286 61Q287 63 287 115V165H28V211L179 442Q332 674 334 675 336 677 355 677H373L379 671V211H471V165H379V114Q379 73 379 66T385 54Q393 47 442 46H471V0H462ZM293 211V545L74 212 183 211H293Z"/></g></g></g></g></svg></mjx-container></th><th><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:0" xmlns="http://www.w3.org/2000/svg" width="2.119ex" height="1.885ex" role="img" focusable="false" viewBox="0 -833.2 936.6 833.2"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mn" transform="translate(533,363) scale(0.707)"><path data-c="33" d="M127 463Q100 463 85 480T69 524Q69 579 117 622T233 665Q268 665 277 664 351 652 390 611T430 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447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mn" transform="translate(533,363) scale(0.707)"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 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309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mn" transform="translate(533,363) scale(0.707)"><path data-c="30" d="M96 585Q152 666 249 666 297 666 345 640T423 548Q460 465 460 320 460 165 417 83 397 41 362 16T301-15 250-22Q224-22 198-16T137 16 82 83Q39 165 39 320 39 494 96 585ZM321 597Q291 629 250 629 208 629 178 597 153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16 290 16 318 46 347 76 354 130T362 333Q362 478 354 524T321 597Z"/></g></g></g></g></svg></mjx-container></th></tr></thead><tbody><tr><td>256</td><td>128</td><td>64</td><td>32</td><td>16</td><td>8</td><td>4</td><td>2</td><td>1</td></tr></tbody></table></div><div class="story post-story"><h2 id="IP地址计算"><a href="#IP地址计算" class="headerlink" title="IP地址计算"></a>IP 地址计算</h2><p><code>172.16.10.1/16</code> 这个 <code>B</code> 类地址的网络地址，广播地址，可用地址数</p><p>IP 地址: <code>172.16.10.1</code></p><p><code>10101100 00010000 00001010 00000001</code></p><p>网络掩码: <code>255.255.0.0</code></p><p><code>11111111 11111111 00000000 00000000</code></p><p>网络地址: <code>127.16.0.0</code></p><p><code>10101100 00010000 00000000 00000000</code></p><p>广播地址: <code>127.16.255.255</code></p><p><code>10101100 00010000 11111111 11111111</code></p><p>IP 地址数:<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.186ex" xmlns="http://www.w3.org/2000/svg" width="11.592ex" height="2.072ex" role="img" focusable="false" viewBox="0 -833.9 5123.7 915.9"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="TeXAtom" transform="translate(533,363) scale(0.707)" data-mjx-texclass="ORD"><g data-mml-node="mn"><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z"/><path data-c="36" d="M42 313Q42 476 123 571T303 666Q372 666 402 630T432 550Q432 525 418 510T379 495Q356 495 341 509T326 548Q326 592 373 601 351 623 311 626 240 626 194 566 147 500 147 364L148 360Q153 366 156 373 197 433 263 433H267Q313 433 348 414 372 400 396 374T435 317Q456 268 456 210V192Q456 169 451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z" transform="translate(500,0)"/></g></g></g><g data-mml-node="mo" transform="translate(1567.9,0)"><path data-c="3D" d="M56 347Q56 360 70 367H707Q722 359 722 347 722 336 708 328L390 327H72Q56 332 56 347ZM56 153Q56 168 72 173H708Q722 163 722 153 722 140 707 133H70Q56 140 56 153Z"/></g><g data-mml-node="mn" transform="translate(2623.7,0)"><path data-c="36" d="M42 313Q42 476 123 571T303 666Q372 666 402 630T432 550Q432 525 418 510T379 495Q356 495 341 509T326 548Q326 592 373 601 351 623 311 626 240 626 194 566 147 500 147 364L148 360Q153 366 156 373 197 433 263 433H267Q313 433 348 414 372 400 396 374T435 317Q456 268 456 210V192Q456 169 451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z"/><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z" transform="translate(500,0)"/><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z" transform="translate(1000,0)"/><path data-c="33" d="M127 463Q100 463 85 480T69 524Q69 579 117 622T233 665Q268 665 277 664 351 652 390 611T430 522Q430 470 396 421T302 350L299 348Q299 347 308 345T337 336 375 315Q457 262 457 175 457 96 395 37T238-22Q158-22 100 21T42 130Q42 158 60 175T105 193Q133 193 151 175T169 130Q169 119 166 110T159 94 148 82 136 74 126 70 118 67L114 66Q165 21 238 21 293 21 321 74 338 107 338 175V195Q338 290 274 322 259 328 213 329L171 330 168 332Q166 335 166 348 166 366 174 366 202 366 232 371 266 376 294 413T322 525V533Q322 590 287 612 265 626 240 626 208 626 181 615T143 592 132 580H135Q138 579 143 578T153 573 165 566 175 555 183 540 186 520Q186 498 172 481T127 463Z" transform="translate(1500,0)"/><path data-c="36" d="M42 313Q42 476 123 571T303 666Q372 666 402 630T432 550Q432 525 418 510T379 495Q356 495 341 509T326 548Q326 592 373 601 351 623 311 626 240 626 194 566 147 500 147 364L148 360Q153 366 156 373 197 433 263 433H267Q313 433 348 414 372 400 396 374T435 317Q456 268 456 210V192Q456 169 451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z" transform="translate(2000,0)"/></g></g></g></svg></mjx-container></p><p>可用 IP 地址数:<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.186ex" xmlns="http://www.w3.org/2000/svg" width="15.489ex" height="2.072ex" role="img" focusable="false" viewBox="0 -833.9 6846.1 915.9"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="TeXAtom" transform="translate(533,363) scale(0.707)" data-mjx-texclass="ORD"><g data-mml-node="mn"><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z"/><path data-c="36" d="M42 313Q42 476 123 571T303 666Q372 666 402 630T432 550Q432 525 418 510T379 495Q356 495 341 509T326 548Q326 592 373 601 351 623 311 626 240 626 194 566 147 500 147 364L148 360Q153 366 156 373 197 433 263 433H267Q313 433 348 414 372 400 396 374T435 317Q456 268 456 210V192Q456 169 451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z" transform="translate(500,0)"/></g></g></g><g data-mml-node="mo" transform="translate(1512.3,0)"><path data-c="2212" d="M84 237T84 250 98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z"/></g><g data-mml-node="mn" transform="translate(2512.6,0)"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mo" transform="translate(3290.3,0)"><path data-c="3D" d="M56 347Q56 360 70 367H707Q722 359 722 347 722 336 708 328L390 327H72Q56 332 56 347ZM56 153Q56 168 72 173H708Q722 163 722 153 722 140 707 133H70Q56 140 56 153Z"/></g><g data-mml-node="mn" transform="translate(4346.1,0)"><path data-c="36" d="M42 313Q42 476 123 571T303 666Q372 666 402 630T432 550Q432 525 418 510T379 495Q356 495 341 509T326 548Q326 592 373 601 351 623 311 626 240 626 194 566 147 500 147 364L148 360Q153 366 156 373 197 433 263 433H267Q313 433 348 414 372 400 396 374T435 317Q456 268 456 210V192Q456 169 451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z"/><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z" transform="translate(500,0)"/><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z" transform="translate(1000,0)"/><path data-c="33" d="M127 463Q100 463 85 480T69 524Q69 579 117 622T233 665Q268 665 277 664 351 652 390 611T430 522Q430 470 396 421T302 350L299 348Q299 347 308 345T337 336 375 315Q457 262 457 175 457 96 395 37T238-22Q158-22 100 21T42 130Q42 158 60 175T105 193Q133 193 151 175T169 130Q169 119 166 110T159 94 148 82 136 74 126 70 118 67L114 66Q165 21 238 21 293 21 321 74 338 107 338 175V195Q338 290 274 322 259 328 213 329L171 330 168 332Q166 335 166 348 166 366 174 366 202 366 232 371 266 376 294 413T322 525V533Q322 590 287 612 265 626 240 626 208 626 181 615T143 592 132 580H135Q138 579 143 578T153 573 165 566 175 555 183 540 186 520Q186 498 172 481T127 463Z" transform="translate(1500,0)"/><path data-c="34" d="M462 0Q444 3 333 3 217 3 199 0H190V46H221Q241 46 248 46T265 48 279 53 286 61Q287 63 287 115V165H28V211L179 442Q332 674 334 675 336 677 355 677H373L379 671V211H471V165H379V114Q379 73 379 66T385 54Q393 47 442 46H471V0H462ZM293 211V545L74 212 183 211H293Z" transform="translate(2000,0)"/></g></g></g></svg></mjx-container></p><p>可用 IP 地址范围: <code>172.16.0.1-172.16.255.254</code></p><figure class="highlight plaintext"><table><tbody><tr><td class="code"><pre><span class="line">192.168.54.6/24</span><br><span class="line">网络地址: 192.168.54.0/24</span><br><span class="line">广播地址: 192.168.54.255/24</span><br><span class="line">IP地址数: 2^8=256</span><br><span class="line">可用IP地址数: 2^8-2=254</span><br><span class="line">可用IP地址范围: 192.168.54.1-192.168.54.254</span><br><span class="line"></span><br><span class="line">172.168.54.6 主类</span><br><span class="line">B /16</span><br><span class="line">网络地址: 172.168.0.0/16</span><br><span class="line">广播地址: 172.168.255.255/16</span><br><span class="line">IP地址数: 2^16=65536</span><br><span class="line">可用IP地址数: 2^16-2=65534</span><br><span class="line">可用IP地址范围: 172.168.0.1/16-172.168.255.254/16</span><br><span class="line"></span><br><span class="line">172.168.54.6 /22</span><br><span class="line">172.168.001101 10.6</span><br><span class="line">网络地址: 172.168.52.0/22</span><br><span class="line">广播地址: 172.168.55.255/22</span><br><span class="line">IP地址数: 2^10=1024</span><br><span class="line">可用IP地址数: 2^10-2=1022</span><br><span class="line">可用IP地址范围: 172.168.52.1/22-172.168.55.254/22</span><br></pre></td></tr></tbody></table></figure><p>如果公司有<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.05ex" xmlns="http://www.w3.org/2000/svg" width="2.262ex" height="1.557ex" role="img" focusable="false" viewBox="0 -666 1000 688"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mn"><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z"/><path data-c="36" d="M42 313Q42 476 123 571T303 666Q372 666 402 630T432 550Q432 525 418 510T379 495Q356 495 341 509T326 548Q326 592 373 601 351 623 311 626 240 626 194 566 147 500 147 364L148 360Q153 366 156 373 197 433 263 433H267Q313 433 348 414 372 400 396 374T435 317Q456 268 456 210V192Q456 169 451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z" transform="translate(500,0)"/></g></g></g></svg></mjx-container> 个人，适合的掩码长度是 <code>/26</code></p><p><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.312ex" xmlns="http://www.w3.org/2000/svg" width="11.417ex" height="2.244ex" role="img" focusable="false" viewBox="0 -853.7 5046.3 991.7"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mi" transform="translate(533,363) scale(0.707)"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g></g><g data-mml-node="mo" transform="translate(1212.5,0)"><path data-c="2212" d="M84 237T84 250 98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z"/></g><g data-mml-node="mn" transform="translate(2212.7,0)"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mo" transform="translate(2990.5,0)"><path data-c="2265" d="M83 616Q83 624 89 630T99 636Q107 636 253 568T543 431 687 361Q694 356 694 346T687 331Q685 329 395 192L107 56H101Q83 58 83 76 83 77 83 79 82 86 98 95 117 105 248 167 326 204 378 228L626 346 360 472Q291 505 200 548 112 589 98 597T83 616ZM84-118Q84-108 99-98H678Q694-104 694-118 694-130 679-138H98Q84-131 84-118Z"/></g><g data-mml-node="mn" transform="translate(4046.3,0)"><path data-c="35" d="M164 157Q164 133 148 117T109 101H102Q148 22 224 22 294 22 326 82 345 115 345 210 345 313 318 349 292 382 260 382H254Q176 382 136 314 132 307 129 306T114 304Q97 304 95 310 93 314 93 485V614Q93 664 98 664 100 666 102 666 103 666 123 658T178 642 253 634Q324 634 389 662 397 666 402 666 410 666 410 648V635Q328 538 205 538 174 538 149 544L139 546V374Q158 388 169 396T205 412 256 420Q337 420 393 355T449 201Q449 109 385 44T229-22Q148-22 99 32T50 154Q50 178 61 192T84 210 107 214Q132 214 148 197T164 157Z"/><path data-c="36" d="M42 313Q42 476 123 571T303 666Q372 666 402 630T432 550Q432 525 418 510T379 495Q356 495 341 509T326 548Q326 592 373 601 351 623 311 626 240 626 194 566 147 500 147 364L148 360Q153 366 156 373 197 433 263 433H267Q313 433 348 414 372 400 396 374T435 317Q456 268 456 210V192Q456 169 451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z" transform="translate(500,0)"/></g></g></g></svg></mjx-container></p><p><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.312ex" xmlns="http://www.w3.org/2000/svg" width="5.451ex" height="1.882ex" role="img" focusable="false" viewBox="0 -694 2409.6 832"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mi"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g><g data-mml-node="mo" transform="translate(853.8,0)"><path data-c="2265" d="M83 616Q83 624 89 630T99 636Q107 636 253 568T543 431 687 361Q694 356 694 346T687 331Q685 329 395 192L107 56H101Q83 58 83 76 83 77 83 79 82 86 98 95 117 105 248 167 326 204 378 228L626 346 360 472Q291 505 200 548 112 589 98 597T83 616ZM84-118Q84-108 99-98H678Q694-104 694-118 694-130 679-138H98Q84-131 84-118Z"/></g><g data-mml-node="mn" transform="translate(1909.6,0)"><path data-c="36" d="M42 313Q42 476 123 571T303 666Q372 666 402 630T432 550Q432 525 418 510T379 495Q356 495 341 509T326 548Q326 592 373 601 351 623 311 626 240 626 194 566 147 500 147 364L148 360Q153 366 156 373 197 433 263 433H267Q313 433 348 414 372 400 396 374T435 317Q456 268 456 210V192Q456 169 451 149 440 90 387 34T253-22Q225-22 199-14T143 16 92 75 56 172 42 313ZM257 397Q227 397 205 380T171 335 154 278 148 216Q148 133 160 97T198 39Q222 21 251 21 302 21 329 59 342 77 347 104T352 209Q352 289 347 316T329 361Q302 397 257 397Z"/></g></g></g></svg></mjx-container></p><p>11111111.11111111.11111111.11000000</p><p>255.255.255.192</p><figure class="highlight plaintext"><table><tbody><tr><td class="code"><pre><span class="line">10.1.56.6 /28</span><br><span class="line">10.1.56.0000 0110</span><br><span class="line">网络地址: 10.1.56.0/28</span><br><span class="line">广播地址: 10.1.56.15/28</span><br><span class="line">IP地址数: 2^4=16</span><br><span class="line">可用IP地址数: 2^4-2=14</span><br><span class="line">可用IP地址范围: 10.1.56.1/28-10.1.56.14/28</span><br><span class="line"></span><br><span class="line">192.172.168.169 /27</span><br><span class="line">192.172.168.101 01001</span><br><span class="line">网络地址: 192.172.168.160/27</span><br><span class="line">广播地址: 192.172.168.191/27</span><br><span class="line">IP地址数: 2^5=32</span><br><span class="line">可用IP地址数: 2^5-2=30</span><br><span class="line">可用IP地址范围: 192.172.168.161/27-192.172.168.190/27</span><br><span class="line"></span><br><span class="line">192.168.39.48 /19</span><br><span class="line">192.168.001 00111.48</span><br><span class="line">网络地址: 192.168.32.0/19</span><br><span class="line">广播地址: 192.168.63.255/19</span><br><span class="line">IP地址数: 2^13=8192</span><br><span class="line">可用IP地址数: 2^13-2=8190</span><br><span class="line">可用IP地址范围: 192.168.32.1/19-192.168.63.254/19</span><br><span class="line"></span><br><span class="line">192.168.56.9 /19</span><br><span class="line">192.168.001 11000.9</span><br><span class="line">网络地址: 192.168.32.0/19</span><br><span class="line">广播地址: 192.168.63.255/19</span><br><span class="line">IP地址数: 2^13=8192</span><br><span class="line">可用IP地址数: 2^13-2=8190</span><br><span class="line">可用IP地址范围: 192.168.32.1/19-192.168.63.254/19</span><br><span class="line"></span><br><span class="line">172.169.1.9 /6</span><br><span class="line">101011 00.169.1.9</span><br><span class="line">网络地址: 172.0.0.0/6</span><br><span class="line">广播地址: 175.255.255.255/6</span><br><span class="line">IP地址数: 2^26=67,108,864</span><br><span class="line">可用IP地址数: 2^26-2=67,108,862</span><br><span class="line">可用IP地址范围: 172.0.0.1/6-175.255.255.254/6</span><br></pre></td></tr></tbody></table></figure></div><div class="story post-story"><h2 id="划分子网"><a href="#划分子网" class="headerlink" title="划分子网"></a>划分子网</h2><p>向主机位借位形成子网.</p><p>可变长子网掩码 VLSM</p><p>[例]</p><p>有一个 C 类网络地址 192.168.1.0/24 , 使用可变长子网掩码给三个子网分别分配 IP 地址 10 台 8 台 5 台</p><p>方法 1:<br><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.312ex" xmlns="http://www.w3.org/2000/svg" width="6.427ex" height="1.841ex" role="img" focusable="false" viewBox="0 -675.5 2840.8 813.5"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mi" transform="translate(533,363) scale(0.707)"><path data-c="1D45B" d="M21 287Q22 293 24 303T36 341 56 388 89 425 135 442Q171 442 195 424T225 390 231 369Q231 367 232 367L243 378Q304 442 382 442 436 442 469 415T503 336 465 179 427 52Q427 26 444 26 450 26 453 27 482 32 505 65T540 145Q542 153 560 153 580 153 580 145 580 144 576 130 568 101 554 73T508 17 439-10Q392-10 371 17T350 73Q350 92 386 193T423 345Q423 404 379 404H374Q288 404 229 303L222 291 189 157Q156 26 151 16 138-11 108-11 95-11 87-5T76 7 74 17Q74 30 112 180T152 343Q153 348 153 366 153 405 129 405 91 405 66 305 60 285 60 284 58 278 41 278H27Q21 284 21 287Z"/></g></g><g data-mml-node="mo" transform="translate(1285,0)"><path data-c="2265" d="M83 616Q83 624 89 630T99 636Q107 636 253 568T543 431 687 361Q694 356 694 346T687 331Q685 329 395 192L107 56H101Q83 58 83 76 83 77 83 79 82 86 98 95 117 105 248 167 326 204 378 228L626 346 360 472Q291 505 200 548 112 589 98 597T83 616ZM84-118Q84-108 99-98H678Q694-104 694-118 694-130 679-138H98Q84-131 84-118Z"/></g><g data-mml-node="mn" transform="translate(2340.8,0)"><path data-c="33" d="M127 463Q100 463 85 480T69 524Q69 579 117 622T233 665Q268 665 277 664 351 652 390 611T430 522Q430 470 396 421T302 350L299 348Q299 347 308 345T337 336 375 315Q457 262 457 175 457 96 395 37T238-22Q158-22 100 21T42 130Q42 158 60 175T105 193Q133 193 151 175T169 130Q169 119 166 110T159 94 148 82 136 74 126 70 118 67L114 66Q165 21 238 21 293 21 321 74 338 107 338 175V195Q338 290 274 322 259 328 213 329L171 330 168 332Q166 335 166 348 166 366 174 366 202 366 232 371 266 376 294 413T322 525V533Q322 590 287 612 265 626 240 626 208 626 181 615T143 592 132 580H135Q138 579 143 578T153 573 165 566 175 555 183 540 186 520Q186 498 172 481T127 463Z"/></g></g></g></svg></mjx-container></p><p><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.312ex" xmlns="http://www.w3.org/2000/svg" width="5.506ex" height="1.819ex" role="img" focusable="false" viewBox="0 -666 2433.6 804"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mi"><path data-c="1D45B" d="M21 287Q22 293 24 303T36 341 56 388 89 425 135 442Q171 442 195 424T225 390 231 369Q231 367 232 367L243 378Q304 442 382 442 436 442 469 415T503 336 465 179 427 52Q427 26 444 26 450 26 453 27 482 32 505 65T540 145Q542 153 560 153 580 153 580 145 580 144 576 130 568 101 554 73T508 17 439-10Q392-10 371 17T350 73Q350 92 386 193T423 345Q423 404 379 404H374Q288 404 229 303L222 291 189 157Q156 26 151 16 138-11 108-11 95-11 87-5T76 7 74 17Q74 30 112 180T152 343Q153 348 153 366 153 405 129 405 91 405 66 305 60 285 60 284 58 278 41 278H27Q21 284 21 287Z"/></g><g data-mml-node="mo" transform="translate(877.8,0)"><path data-c="2265" d="M83 616Q83 624 89 630T99 636Q107 636 253 568T543 431 687 361Q694 356 694 346T687 331Q685 329 395 192L107 56H101Q83 58 83 76 83 77 83 79 82 86 98 95 117 105 248 167 326 204 378 228L626 346 360 472Q291 505 200 548 112 589 98 597T83 616ZM84-118Q84-108 99-98H678Q694-104 694-118 694-130 679-138H98Q84-131 84-118Z"/></g><g data-mml-node="mn" transform="translate(1933.6,0)"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g></g></g></svg></mjx-container></p><p>4 个子网</p><p>00 000000 0/26<br>01 000000 64/26<br>10 000000 128/26<br>11 000000 192/26</p><p>方法 2:</p><p><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.312ex" xmlns="http://www.w3.org/2000/svg" width="11.417ex" height="2.244ex" role="img" focusable="false" viewBox="0 -853.7 5046.3 991.7"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mi" transform="translate(533,363) scale(0.707)"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g></g><g data-mml-node="mo" transform="translate(1212.5,0)"><path data-c="2212" d="M84 237T84 250 98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z"/></g><g data-mml-node="mn" transform="translate(2212.7,0)"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mo" transform="translate(2990.5,0)"><path data-c="2265" d="M83 616Q83 624 89 630T99 636Q107 636 253 568T543 431 687 361Q694 356 694 346T687 331Q685 329 395 192L107 56H101Q83 58 83 76 83 77 83 79 82 86 98 95 117 105 248 167 326 204 378 228L626 346 360 472Q291 505 200 548 112 589 98 597T83 616ZM84-118Q84-108 99-98H678Q694-104 694-118 694-130 679-138H98Q84-131 84-118Z"/></g><g data-mml-node="mn" transform="translate(4046.3,0)"><path data-c="31" d="M213 578 200 573Q186 568 160 563T102 556H83V602H102Q149 604 189 617T245 641 273 663Q275 666 285 666 294 666 302 660V361L303 61Q310 54 315 52T339 48 401 46H427V0H416Q395 3 257 3 121 3 100 0H88V46H114Q136 46 152 46T177 47 193 50 201 52 207 57 213 61V578Z"/><path data-c="30" d="M96 585Q152 666 249 666 297 666 345 640T423 548Q460 465 460 320 460 165 417 83 397 41 362 16T301-15 250-22Q224-22 198-16T137 16 82 83Q39 165 39 320 39 494 96 585ZM321 597Q291 629 250 629 208 629 178 597 153 571 145 525T137 333Q137 175 145 125T181 46Q209 16 250 16 290 16 318 46 347 76 354 130T362 333Q362 478 354 524T321 597Z" transform="translate(500,0)"/></g></g></g></svg></mjx-container></p><p><mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.312ex" xmlns="http://www.w3.org/2000/svg" width="5.451ex" height="1.882ex" role="img" focusable="false" viewBox="0 -694 2409.6 832"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mi"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g><g data-mml-node="mo" transform="translate(853.8,0)"><path data-c="2265" d="M83 616Q83 624 89 630T99 636Q107 636 253 568T543 431 687 361Q694 356 694 346T687 331Q685 329 395 192L107 56H101Q83 58 83 76 83 77 83 79 82 86 98 95 117 105 248 167 326 204 378 228L626 346 360 472Q291 505 200 548 112 589 98 597T83 616ZM84-118Q84-108 99-98H678Q694-104 694-118 694-130 679-138H98Q84-131 84-118Z"/></g><g data-mml-node="mn" transform="translate(1909.6,0)"><path data-c="34" d="M462 0Q444 3 333 3 217 3 199 0H190V46H221Q241 46 248 46T265 48 279 53 286 61Q287 63 287 115V165H28V211L179 442Q332 674 334 675 336 677 355 677H373L379 671V211H471V165H379V114Q379 73 379 66T385 54Q393 47 442 46H471V0H462ZM293 211V545L74 212 183 211H293Z"/></g></g></g></svg></mjx-container></p><p>16 个子网</p><p>0000 0000</p><p>0001 0000</p><p>….</p><p>[例]</p><p>192.168.1.2/24 (主机位 8)<br>共有 25 个地址需求<br>求子网网络号，掩码。广播地址，可划分子网数</p><figure class="highlight plaintext"><table><tbody><tr><td class="code"><pre><span class="line">2^h-2>=25</span><br><span class="line">h>=5 主机位 5</span><br><span class="line">n=3</span><br><span class="line">可划分2^3=8个子网</span><br><span class="line">掩码</span><br><span class="line">255.255.255.111 00000</span><br><span class="line">255.255.255.224</span><br><span class="line">/27</span><br><span class="line">子网网络号</span><br><span class="line">192.168.1.000 00000 192.168.1.0/27</span><br><span class="line">192.168.1.001 00000 192.168.1.32/27</span><br><span class="line">192.168.1.010 00000 192.168.1.64/27</span><br><span class="line">192.168.1.011 00000 192.168.1.96/27</span><br><span class="line">192.168.1.100 00000 192.168.1.128/27</span><br><span class="line">192.168.1.101 00000 192.168.1.160/27</span><br><span class="line">192.168.1.110 00000 192.168.1.192/27</span><br><span class="line">192.168.1.111 00000 192.168.1.224/27</span><br><span class="line">广播地址</span><br><span class="line">192.168.1.000 11111 /27</span><br><span class="line">192.168.1.001 11111 /27</span><br><span class="line">192.168.1.010 11111 /27</span><br><span class="line">192.168.1.011 11111 /27</span><br><span class="line">192.168.1.100 11111 /27</span><br><span class="line">192.168.1.101 11111 /27</span><br><span class="line">192.168.1.110 11111 /27</span><br><span class="line">192.168.1.111 11111 /27</span><br></pre></td></tr></tbody></table></figure><p>[例]</p><p>某公司 4 个部门，每个部门最多 36 人<br>192.168.10.0/24 (主机位 8)<br>划分出合适的网络<br>掩码<br>网络号<br>子网数目</p><figure class="highlight plaintext"><table><tbody><tr><td class="code"><pre><span class="line">2^h-2>=36</span><br><span class="line">h>=6</span><br><span class="line">n=2</span><br><span class="line">子网数目 2^2=4</span><br><span class="line">掩码</span><br><span class="line">255.255.255.11 000000</span><br><span class="line">255.255.255.192</span><br><span class="line">网络号</span><br><span class="line">192.168.10.00 000000 192.168.10.0/26</span><br><span class="line">192.168.10.01 000000 192.168.10.64/26</span><br><span class="line">192.168.10.10 000000 192.168.10.128/26</span><br><span class="line">192.168.10.11 000000 192.168.10.192/26</span><br></pre></td></tr></tbody></table></figure></div><div class="story post-story"><h2 id="IP编址"><a href="#IP编址" class="headerlink" title="IP编址"></a>IP 编址</h2><p>一个网络内拥有的 IP 地址数量为<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:0" xmlns="http://www.w3.org/2000/svg" width="2.24ex" height="1.932ex" role="img" focusable="false" viewBox="0 -853.7 990.3 853.7"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mi" transform="translate(533,363) scale(0.707)"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g></g></g></g></svg></mjx-container> (<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.025ex" xmlns="http://www.w3.org/2000/svg" width="1.303ex" height="1.595ex" role="img" focusable="false" viewBox="0 -694 576 705"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mi"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g></g></g></svg></mjx-container>代表主机位位数).</p><p>因为网络号和广播地址不可以配置在设备上，所以实际可用主机地址数为<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.186ex" xmlns="http://www.w3.org/2000/svg" width="6.137ex" height="2.117ex" role="img" focusable="false" viewBox="0 -853.7 2712.7 935.7"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mi" transform="translate(533,363) scale(0.707)"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g></g><g data-mml-node="mo" transform="translate(1212.5,0)"><path data-c="2212" d="M84 237T84 250 98 270H679Q694 262 694 250T679 230H98Q84 237 84 250Z"/></g><g data-mml-node="mn" transform="translate(2212.7,0)"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g></g></g></svg></mjx-container>.</p><p>如果两个 IP 地址的网络位相同，则这两个地址属于同一个网络，可以不通过网关设备或路由器直接通信.</p><p>如果两个 IP 地址的网络位不同，则需要借助网关设备和路由器进行通信.</p><p>使用默认掩码的就是有类地址.</p><p>无类地址就是经过子网划分的 IP 地址.</p><p><code>VLSM</code>: 可变长子网掩码.</p><p>子网掩码变长，主机位变少，<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:0" xmlns="http://www.w3.org/2000/svg" width="2.24ex" height="1.932ex" role="img" focusable="false" viewBox="0 -853.7 990.3 853.7"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mi" transform="translate(533,363) scale(0.707)"><path data-c="210E" d="M137 683Q138 683 209 688T282 694Q294 694 294 685 294 674 258 534 220 386 220 383 220 381 227 388 288 442 357 442 411 442 444 415T478 336Q478 285 440 178T402 50Q403 36 407 31T422 26Q450 26 474 56T513 138Q516 149 519 151T535 153Q555 153 555 145 555 144 551 130 535 71 500 33 466-10 419-10H414Q367-10 346 17T325 74Q325 90 361 192T398 345Q398 404 354 404H349Q266 404 205 306L198 293 164 158Q132 28 127 16 114-11 83-11 69-11 59-2T48 16Q48 30 121 320L195 616Q195 629 188 632T149 637H128Q122 643 122 645T124 664Q129 683 137 683Z"/></g></g></g></g></svg></mjx-container> 就会变少，主机数目减少，避免地址浪费。主机位长度缩减，网络位就会增加.</p><p>一个子网位能分出两个子网<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:0" xmlns="http://www.w3.org/2000/svg" width="2.279ex" height="1.528ex" role="img" focusable="false" viewBox="0 -675.5 1007.3 675.5"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="msup"><g data-mml-node="mn"><path data-c="32" d="M109 429Q82 429 66 447T50 491Q50 562 103 614T235 666Q326 666 387 610T449 465Q449 422 429 383T381 315 301 241Q265 210 201 149L142 93 218 92Q375 92 385 97 392 99 409 186V189H449V186Q448 183 436 95T421 3V0H50V19 31Q50 38 56 46T86 81Q115 113 136 137 145 147 170 174T204 211 233 244 261 278 284 308 305 340 320 369 333 401 340 431 343 464Q343 527 309 573T212 619Q179 619 154 602T119 569 109 550Q109 549 114 549 132 549 151 535T170 489Q170 464 154 447T109 429Z"/></g><g data-mml-node="mi" transform="translate(533,363) scale(0.707)"><path data-c="1D45B" d="M21 287Q22 293 24 303T36 341 56 388 89 425 135 442Q171 442 195 424T225 390 231 369Q231 367 232 367L243 378Q304 442 382 442 436 442 469 415T503 336 465 179 427 52Q427 26 444 26 450 26 453 27 482 32 505 65T540 145Q542 153 560 153 580 153 580 145 580 144 576 130 568 101 554 73T508 17 439-10Q392-10 371 17T350 73Q350 92 386 193T423 345Q423 404 379 404H374Q288 404 229 303L222 291 189 157Q156 26 151 16 138-11 108-11 95-11 87-5T76 7 74 17Q74 30 112 180T152 343Q153 348 153 366 153 405 129 405 91 405 66 305 60 285 60 284 58 278 41 278H27Q21 284 21 287Z"/></g></g></g></g></svg></mjx-container> (<mjx-container class="MathJax" jax="SVG"><svg style="vertical-align:-.025ex" xmlns="http://www.w3.org/2000/svg" width="1.357ex" height="1.025ex" role="img" focusable="false" viewBox="0 -442 600 453"><g stroke="currentColor" fill="currentColor" stroke-width="0" transform="scale(1,-1)"><g data-mml-node="math"><g data-mml-node="mi"><path data-c="1D45B" d="M21 287Q22 293 24 303T36 341 56 388 89 425 135 442Q171 442 195 424T225 390 231 369Q231 367 232 367L243 378Q304 442 382 442 436 442 469 415T503 336 465 179 427 52Q427 26 444 26 450 26 453 27 482 32 505 65T540 145Q542 153 560 153 580 153 580 145 580 144 576 130 568 101 554 73T508 17 439-10Q392-10 371 17T350 73Q350 92 386 193T423 345Q423 404 379 404H374Q288 404 229 303L222 291 189 157Q156 26 151 16 138-11 108-11 95-11 87-5T76 7 74 17Q74 30 112 180T152 343Q153 348 153 366 153 405 129 405 91 405 66 305 60 285 60 284 58 278 41 278H27Q21 284 21 287Z"/></g></g></g></svg></mjx-container> 是子网位位数).</p><p><code>CIDR</code>: 无类域间路由 (VLSM 逆运算)</p><p>子网掩码除了 VLSM 以外，还可以变短进行网络信息的汇总，这种操作方式就是 CIDR.</p><p>将不同网络的网络号中共同发生变化的位置当作主机位进行处理，之后对外发布，起到节省设备资源的作用.</p></div></div><div class="footer"></div><div class="article-meta" id="bottom"><div class="new-meta-box"></div></div><div class="prev-next"><a class="prev" 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pjax"><header><a href="/notes/"><i class="fa-duotone fa-book fa-fw" aria-hidden="true"></i> <span class="name">Notes</span></a></header><div class="content"></div></section><section class="widget list group desktop mobile pjax"><header><i class="fa-duotone fa-chart-network fa-fw" aria-hidden="true"></i> <span class="name">数据通信网络</span></header><div class="content"><ul class="list entry navigation"><li><a class="flat-box" title="/notes/datacom/" href="/notes/datacom/" active-action="action-notesdatacom"><div class="name"> Welcome</div></a></li><li><a class="flat-box" title="/notes/datacom/1" href="/notes/datacom/1" active-action="action-notesdatacom1"><div class="name"> 网络通信</div></a></li><li><a class="flat-box" title="/notes/datacom/2" href="/notes/datacom/2" active-action="action-notesdatacom2"><div class="name"> 传输介质</div></a></li><li><a class="flat-box" title="/notes/datacom/3" href="/notes/datacom/3" active-action="action-notesdatacom3"><div class="name"> 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href="/notes/datacom/23" active-action="action-notesdatacom23"><div class="name"> OSPF特殊区域</div></a></li><li><a class="flat-box" title="/notes/datacom/24" href="/notes/datacom/24" active-action="action-notesdatacom24"><div class="name"> BGP</div></a></li><li><a class="flat-box" title="/notes/datacom/25" href="/notes/datacom/25" active-action="action-notesdatacom25"><div class="name"> VRF 虚拟路由转发</div></a></li><li><a class="flat-box" title="/notes/datacom/26" href="/notes/datacom/26" active-action="action-notesdatacom26"><div class="name"> VRRP</div></a></li><li><a class="flat-box" title="/notes/datacom/27" href="/notes/datacom/27" active-action="action-notesdatacom27"><div class="name"> 防火墙</div></a></li><li><a class="flat-box" title="/notes/datacom/28" href="/notes/datacom/28" active-action="action-notesdatacom28"><div class="name"> WLAN</div></a></li><li><a class="flat-box" title="/notes/datacom/29" href="/notes/datacom/29" active-action="action-notesdatacom29"><div class="name"> 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