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| 3 | · | 3 | ·a4b2db16c4cab1640ea52da969fc7594·1136688·doc·optional·bird-doc_1.6.8-2.1_all.deb |
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| 1 | Package:·bird-doc | 1 | Package:·bird-doc |
| 2 | Source:·bird | 2 | Source:·bird |
| 3 | Version:·1.6.8-2.1 | 3 | Version:·1.6.8-2.1 |
| 4 | Architecture:·all | 4 | Architecture:·all |
| 5 | Maintainer:·Ondřej·Surý·<ondrej@debian.org> | 5 | Maintainer:·Ondřej·Surý·<ondrej@debian.org> |
| 6 | Installed-Size:·193 | 6 | Installed-Size:·1934 |
| 7 | Section:·doc | 7 | Section:·doc |
| 8 | Priority:·optional | 8 | Priority:·optional |
| 9 | Homepage:·http://bird.network.cz/ | 9 | Homepage:·http://bird.network.cz/ |
| 10 | Description:·Internet·Routing·Daemon·-·documentation | 10 | Description:·Internet·Routing·Daemon·-·documentation |
| 11 | ·BIRD·is·an·Internet·routing·daemon·with·full·support·for·all·the·major | 11 | ·BIRD·is·an·Internet·routing·daemon·with·full·support·for·all·the·major |
| 12 | ·routing·protocols.·It·allows·redistribution·between·protocols·with·a | 12 | ·routing·protocols.·It·allows·redistribution·between·protocols·with·a |
| 13 | ·powerful·route·filtering·syntax·and·an·easy-to-use·configuration | 13 | ·powerful·route·filtering·syntax·and·an·easy-to-use·configuration |
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| 319 | ········import·all; | 319 | ········import·all; |
| 320 | ········interface·"*"; | 320 | ········interface·"*"; |
| 321 | } | 321 | } |
| 322 | </PRE> | 322 | </PRE> |
| 323 | <HR> | 323 | <HR> |
| 324 | <P> | 324 | <P> |
| 325 | <P> | 325 | <P> |
| 326 | <H2><A·NAME="s1">1.·BIRD·Design</A></H2> | ||
| 327 | <H2><A·NAME="ss1.1">1.1·Introduction</A> | ||
| 328 | </H2> | ||
| 329 | <P>This·document·describes·the·internal·workings·of·BIRD,·its·architecture, | ||
| 330 | design·decisions·and·rationale·behind·them.·It·also·contains·documentation·on | ||
| 331 | all·the·essential·components·of·the·system·and·their·interfaces. | ||
| 332 | <P> | ||
| 333 | <P>Routing·daemons·are·complicated·things·which·need·to·act·in·real·time | ||
| 334 | to·complex·sequences·of·external·events,·respond·correctly·even·to·the·most·erroneous·behavior | ||
| 335 | of·their·environment·and·still·handle·enormous·amount·of·data·with·reasonable | ||
| 336 | speed.·Due·to·all·of·this,·their·design·is·very·tricky·as·one·needs·to·carefully | ||
| 337 | balance·between·efficiency,·stability·and·(last,·but·not·least)·simplicity·of | ||
| 338 | the·program·and·it·would·be·possible·to·write·literally·hundreds·of·pages·about | ||
| 339 | all·of·these·issues.·In·accordance·to·the·famous·quote·of·Anton·Chekhov·"Shortness | ||
| 340 | is·a·sister·of·talent",·we've·tried·to·write·a·much·shorter·document·highlighting | ||
| 341 | the·most·important·stuff·and·leaving·the·boring·technical·details·better·explained | ||
| 342 | by·the·program·source·itself·together·with·comments·contained·therein. | ||
| 343 | <P> | ||
| 344 | <H2><A·NAME="ss3.2">3.2·Global·options</A> | 326 | <H2><A·NAME="ss3.2">3.2·Global·options</A> |
| 345 | <@@label>global-opts</H2> | 327 | <@@label>global-opts</H2> |
| 346 | <P> | 328 | <P> |
| 347 | <DL> | 329 | <DL> |
| 348 | <DT><CODE> | 330 | <DT><CODE> |
| 349 | <@@label>opt-include | 331 | <@@label>opt-include |
| Offset 526, 155 lines modified | Offset 506, 14 lines modified | ||
| 526 | <P> | 506 | <P> |
| 527 | <DT><CODE> | 507 | <DT><CODE> |
| 528 | <@@label>opt-eval | 508 | <@@label>opt-eval |
| 529 | eval·<I>expr</I></CODE><DD><P>Evaluates·given·filter·expression.·It·is·used·by·us·for···testing·of·filters. | 509 | eval·<I>expr</I></CODE><DD><P>Evaluates·given·filter·expression.·It·is·used·by·us·for···testing·of·filters. |
| 530 | </DL> | 510 | </DL> |
| 531 | <P> | 511 | <P> |
| 532 | <P> | 512 | <P> |
| 533 | <H2><A·NAME="ss1.2">1.2·Design·goals</A> | ||
| 534 | </H2> | ||
| 535 | <P>When·planning·the·architecture·of·BIRD,·we've·taken·a·close·look·at·the·other·existing·routing | ||
| 536 | daemons·and·also·at·some·of·the·operating·systems·used·on·dedicated·routers,·gathered·all·important | ||
| 537 | features·and·added·lots·of·new·ones·to·overcome·their·shortcomings·and·to·better·match·the·requirements | ||
| 538 | of·routing·in·today's·Internet:·IPv6,·policy·routing,·route·filtering·and·so·on.·From·this | ||
| 539 | planning,·the·following·set·of·design·goals·has·arisen: | ||
| 540 | <P> | ||
| 541 | <UL> | ||
| 542 | <LI><I>Support·all·the·standard·routing·protocols·and·make·it·easy·to·add·new·ones.</I> | ||
| 543 | This·leads·to·modularity·and·clean·separation·between·the·core·and·the·protocols. | ||
| 544 | </LI> | ||
| 545 | <LI><I>Support·both·IPv4·and·IPv6·in·the·same·source·tree,·re-using·most·of·the·code.</I> | ||
| 546 | This·leads·to·abstraction·of·IP·addresses·and·operations·on·them. | ||
| 547 | </LI> | ||
| 548 | <LI><I>Minimize·OS·dependent·code·to·make·porting·as·easy·as·possible.</I> | ||
| 549 | Unfortunately,·such·code·cannot·be·avoided·at·all·as·the·details·of·communication·with | ||
| 550 | the·IP·stack·differ·from·OS·to·OS·and·they·often·vary·even·between·different | ||
| 551 | versions·of·the·same·OS.·But·we·can·isolate·such·code·in·special·modules·and | ||
| 552 | do·the·porting·by·changing·or·replacing·just·these·modules. | ||
| 553 | Also,·don't·rely·on·specific·features·of·various·operating·systems,·but·be·able | ||
| 554 | to·make·use·of·them·if·they·are·available. | ||
| 555 | </LI> | ||
| 556 | <LI><I>Allow·multiple·routing·tables.</I> | ||
| 557 | Easily·solvable·by·abstracting·out·routing·tables·and·the·corresponding·operations. | ||
| 558 | </LI> | ||
| 559 | <LI><I>Offer·powerful·route·filtering.</I> | ||
| 560 | There·already·were·several·attempts·to·incorporate·route·filters·to·a·dynamic·router, | ||
| 561 | but·most·of·them·have·used·simple·sequences·of·filtering·rules·which·were·very·inflexible | ||
| 562 | and·hard·to·use·for·non-trivial·filters.·We've·decided·to·employ·a·simple·loop-free | ||
| 563 | programming·language·having·access·to·all·the·route·attributes·and·being·able·to | ||
| 564 | modify·the·most·of·them. | ||
| 565 | </LI> | ||
| 566 | <LI><I>Support·easy·configuration·and·re-configuration.</I> | ||
| 567 | Most·routers·use·a·simple·configuration·language·designed·ad·hoc·with·no·structure·at·all | ||
| 568 | and·allow·online·changes·of·configuration·by·using·their·command-line·interface,·thus | ||
| 569 | any·complex·re-configurations·are·hard·to·achieve·without·replacing·the·configuration | ||
| 570 | file·and·restarting·the·whole·router.·We've·decided·to·use·a·more·general·approach:·to | ||
| 571 | have·a·configuration·defined·in·a·context-free·language·with·blocks·and·nesting,·to | ||
| 572 | perform·all·configuration·changes·by·editing·the·configuration·file,·but·to·be·able | ||
| 573 | to·read·the·new·configuration·and·smoothly·adapt·to·it·without·disturbing·parts·of | ||
| 574 | the·routing·process·which·are·not·affected·by·the·change. | ||
| 575 | </LI> | ||
| 576 | <LI><I>Be·able·to·be·controlled·online.</I> | ||
| 577 | In·addition·to·the·online·reconfiguration,·a·routing·daemon·should·be·able·to·communicate | ||
| 578 | with·the·user·and·with·many·other·programs·(primarily·scripts·used·for·network·maintenance) | ||
| 579 | in·order·to·make·it·possible·to·inspect·contents·of·routing·tables,·status·of·all | ||
| 580 | routing·protocols·and·also·to·control·their·behavior·(disable,·enable·or·reset·a·protocol·without·restarting·all·the·others).·To·achieve | ||
| 581 | this,·we·implement·a·simple·command-line·protocol·based·on·those·used·by·FTP·and·SMTP | ||
| 582 | (that·is·textual·commands·and·textual·replies·accompanied·by·a·numeric·code·which·makes | ||
| 583 | them·both·readable·to·a·human·and·easy·to·recognize·in·software). | ||
| 584 | </LI> | ||
| 585 | <LI><I>Respond·to·all·events·in·real·time.</I> | ||
| 586 | A·typical·solution·to·this·problem·is·to·use·lots·of·threads·to·separate·the·workings | ||
| 587 | of·all·the·routing·protocols·and·also·of·the·user·interface·parts·and·to·hope·that | ||
| 588 | the·scheduler·will·assign·time·to·them·in·a·fair·enough·manner.·This·is·surely·a·good | ||
| 589 | solution,·but·we·have·resisted·the·temptation·and·preferred·to·avoid·the·overhead·of·threading | ||
| 590 | and·the·large·number·of·locks·involved·and·preferred·a·event·driven·architecture·with | ||
| 591 | our·own·scheduling·of·events.·An·unpleasant·consequence·of·such·an·approach | ||
| 592 | is·that·long·lasting·tasks·must·be·split·to·more·parts·linked·by·special | ||
| 593 | events·or·timers·to·make·the·CPU·available·for·other·tasks·as·well. | ||
| 594 | </LI> | ||
| 595 | </UL> | ||
| 596 | <P> | ||
| 597 | <H2><A·NAME="ss1.3">1.3·Architecture</A> | ||
| 598 | </H2> | ||
| 599 | <P>The·requirements·set·above·have·lead·to·a·simple·modular·architecture·containing | ||
| 600 | the·following·types·of·modules: | ||
| 601 | <P> | ||
| 602 | <DL> | ||
| 603 | <P> | ||
| 604 | <DT>Core·modules<DD><P>implement·the·core·functions·of·BIRD:·taking·care | ||
| 605 | of·routing·tables,·keeping·protocol·status,·interacting·with·the·user·using | ||
| 606 | the·Command-Line·Interface·(to·be·called·CLI·in·the·rest·of·this·document) | ||
| 607 | etc. | ||
| 608 | <P> | ||
| 609 | <DT>Library·modules<DD><P>form·a·large·set·of·various·library·functions | ||
| 610 | implementing·several·data·abstractions,·utility·functions·and·also·functions | ||
| 611 | which·are·a·part·of·the·standard·libraries·on·some·systems,·but·missing·on·other | ||
| 612 | ones. | ||
| 613 | <P> | ||
| 614 | <DT>Resource·management·modules<DD><P>take·care·of·resources,·their·allocation | ||
| 615 | and·automatic·freeing·when·the·module·having·requested·shuts·itself·down. | ||
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| 221 | protocol·rip·{ | 221 | protocol·rip·{ |
| 222 | ········export·all; | 222 | ········export·all; |
| 223 | ········import·all; | 223 | ········import·all; |
| 224 | ········interface·"*"; | 224 | ········interface·"*"; |
| 225 | } | 225 | } |
| 226 | =============================================================================== | 226 | =============================================================================== |
| 227 | *****·1.·BIRD·Design·***** | ||
| 228 | *****·1.1·Introduction·***** | ||
| 229 | This·document·describes·the·internal·workings·of·BIRD,·its·architecture,·design | ||
| 230 | decisions·and·rationale·behind·them.·It·also·contains·documentation·on·all·the | ||
| 231 | essential·components·of·the·system·and·their·interfaces. | ||
| 232 | Routing·daemons·are·complicated·things·which·need·to·act·in·real·time·to | ||
| 233 | complex·sequences·of·external·events,·respond·correctly·even·to·the·most | ||
| 234 | erroneous·behavior·of·their·environment·and·still·handle·enormous·amount·of | ||
| 235 | data·with·reasonable·speed.·Due·to·all·of·this,·their·design·is·very·tricky·as | ||
| 236 | one·needs·to·carefully·balance·between·efficiency,·stability·and·(last,·but·not | ||
| 237 | least)·simplicity·of·the·program·and·it·would·be·possible·to·write·literally | ||
| 238 | hundreds·of·pages·about·all·of·these·issues.·In·accordance·to·the·famous·quote | ||
| 239 | of·Anton·Chekhov·"Shortness·is·a·sister·of·talent",·we've·tried·to·write·a·much | ||
| 240 | shorter·document·highlighting·the·most·important·stuff·and·leaving·the·boring | ||
| 241 | technical·details·better·explained·by·the·program·source·itself·together·with | ||
| 242 | comments·contained·therein. | ||
| 243 | *****·3.2·Global·options·<@@label>global-opts·***** | 227 | *****·3.2·Global·options·<@@label>global-opts·***** |
| 244 | ··<@@label>opt-roa-table·roa·table·name·[·{·roa·table·options·...·}·] | 228 | ··<@@label>opt-roa-table·roa·table·name·[·{·roa·table·options·...·}·] |
| 245 | ······Create·a·new·ROA·(Route·Origin·Authorization)·table.·ROA·tables·can·be | 229 | ······Create·a·new·ROA·(Route·Origin·Authorization)·table.·ROA·tables·can·be |
| 246 | ······used·to·validate·route·origination·of·BGP·routes.·A·ROA·table·contains | 230 | ······used·to·validate·route·origination·of·BGP·routes.·A·ROA·table·contains |
| 247 | ······ROA·entries,·each·consist·of·a·network·prefix,·a·max·prefix·length·and·an | 231 | ······ROA·entries,·each·consist·of·a·network·prefix,·a·max·prefix·length·and·an |
| 248 | ······AS·number.·A·ROA·entry·specifies·prefixes·which·could·be·originated·by | 232 | ······AS·number.·A·ROA·entry·specifies·prefixes·which·could·be·originated·by |
| 249 | ······that·AS·number.·ROA·tables·could·be·filled·with·data·from·RPKI·(RFC_6480) | 233 | ······that·AS·number.·ROA·tables·could·be·filled·with·data·from·RPKI·(RFC_6480) |
| Offset 253, 124 lines modified | Offset 237, 14 lines modified | ||
| 253 | ······Currently,·there·is·just·one·option,·roa·prefix·max·num·as·num,·which·can | 237 | ······Currently,·there·is·just·one·option,·roa·prefix·max·num·as·num,·which·can |
| 254 | ······be·used·to·populate·the·ROA·table·with·static·ROA·entries.·The·option·may | 238 | ······be·used·to·populate·the·ROA·table·with·static·ROA·entries.·The·option·may |
| 255 | ······be·used·multiple·times.·Other·entries·can·be·added·dynamically·by·add·roa | 239 | ······be·used·multiple·times.·Other·entries·can·be·added·dynamically·by·add·roa |
| 256 | ······command. | 240 | ······command. |
| 257 | ··<@@label>opt-eval·eval·expr | 241 | ··<@@label>opt-eval·eval·expr |
| 258 | ······Evaluates·given·filter·expression.·It·is·used·by·us·for·testing·of | 242 | ······Evaluates·given·filter·expression.·It·is·used·by·us·for·testing·of |
| 259 | ······filters. | 243 | ······filters. |
| 260 | *****·1.2·Design·goals·***** | ||
| 261 | When·planning·the·architecture·of·BIRD,·we've·taken·a·close·look·at·the·other | ||
| 262 | existing·routing·daemons·and·also·at·some·of·the·operating·systems·used·on | ||
| 263 | dedicated·routers,·gathered·all·important·features·and·added·lots·of·new·ones | ||
| 264 | to·overcome·their·shortcomings·and·to·better·match·the·requirements·of·routing | ||
| 265 | in·today's·Internet:·IPv6,·policy·routing,·route·filtering·and·so·on.·From·this | ||
| 266 | planning,·the·following·set·of·design·goals·has·arisen: | ||
| 267 | ····*·Support·all·the·standard·routing·protocols·and·make·it·easy·to·add·new | ||
| 268 | ······ones.·This·leads·to·modularity·and·clean·separation·between·the·core·and | ||
| 269 | ······the·protocols. | ||
| 270 | ····*·Support·both·IPv4·and·IPv6·in·the·same·source·tree,·re-using·most·of·the | ||
| 271 | ······code.·This·leads·to·abstraction·of·IP·addresses·and·operations·on·them. | ||
| 272 | ····*·Minimize·OS·dependent·code·to·make·porting·as·easy·as·possible. | ||
| 273 | ······Unfortunately,·such·code·cannot·be·avoided·at·all·as·the·details·of | ||
| 274 | ······communication·with·the·IP·stack·differ·from·OS·to·OS·and·they·often·vary | ||
| 275 | ······even·between·different·versions·of·the·same·OS.·But·we·can·isolate·such | ||
| 276 | ······code·in·special·modules·and·do·the·porting·by·changing·or·replacing·just | ||
| 277 | ······these·modules.·Also,·don't·rely·on·specific·features·of·various·operating | ||
| 278 | ······systems,·but·be·able·to·make·use·of·them·if·they·are·available. | ||
| 279 | ····*·Allow·multiple·routing·tables.·Easily·solvable·by·abstracting·out·routing | ||
| 280 | ······tables·and·the·corresponding·operations. | ||
| 281 | ····*·Offer·powerful·route·filtering.·There·already·were·several·attempts·to | ||
| 282 | ······incorporate·route·filters·to·a·dynamic·router,·but·most·of·them·have·used | ||
| 283 | ······simple·sequences·of·filtering·rules·which·were·very·inflexible·and·hard | ||
| 284 | ······to·use·for·non-trivial·filters.·We've·decided·to·employ·a·simple·loop- | ||
| 285 | ······free·programming·language·having·access·to·all·the·route·attributes·and | ||
| 286 | ······being·able·to·modify·the·most·of·them. | ||
| 287 | ····*·Support·easy·configuration·and·re-configuration.·Most·routers·use·a | ||
| 288 | ······simple·configuration·language·designed·ad·hoc·with·no·structure·at·all | ||
| 289 | ······and·allow·online·changes·of·configuration·by·using·their·command-line | ||
| 290 | ······interface,·thus·any·complex·re-configurations·are·hard·to·achieve·without | ||
| 291 | ······replacing·the·configuration·file·and·restarting·the·whole·router.·We've | ||
| 292 | ······decided·to·use·a·more·general·approach:·to·have·a·configuration·defined | ||
| 293 | ······in·a·context-free·language·with·blocks·and·nesting,·to·perform·all | ||
| 294 | ······configuration·changes·by·editing·the·configuration·file,·but·to·be·able | ||
| 295 | ······to·read·the·new·configuration·and·smoothly·adapt·to·it·without·disturbing | ||
| 296 | ······parts·of·the·routing·process·which·are·not·affected·by·the·change. | ||
| 297 | ····*·Be·able·to·be·controlled·online.·In·addition·to·the·online | ||
| 298 | ······reconfiguration,·a·routing·daemon·should·be·able·to·communicate·with·the | ||
| 299 | ······user·and·with·many·other·programs·(primarily·scripts·used·for·network | ||
| 300 | ······maintenance)·in·order·to·make·it·possible·to·inspect·contents·of·routing | ||
| 301 | ······tables,·status·of·all·routing·protocols·and·also·to·control·their | ||
| 302 | ······behavior·(disable,·enable·or·reset·a·protocol·without·restarting·all·the | ||
| 303 | ······others).·To·achieve·this,·we·implement·a·simple·command-line·protocol | ||
| 304 | ······based·on·those·used·by·FTP·and·SMTP·(that·is·textual·commands·and·textual | ||
| 305 | ······replies·accompanied·by·a·numeric·code·which·makes·them·both·readable·to·a | ||
| 306 | ······human·and·easy·to·recognize·in·software). | ||
| 307 | ····*·Respond·to·all·events·in·real·time.·A·typical·solution·to·this·problem·is | ||
| 308 | ······to·use·lots·of·threads·to·separate·the·workings·of·all·the·routing | ||
| 309 | ······protocols·and·also·of·the·user·interface·parts·and·to·hope·that·the | ||
| 310 | ······scheduler·will·assign·time·to·them·in·a·fair·enough·manner.·This·is | ||
| 311 | ······surely·a·good·solution,·but·we·have·resisted·the·temptation·and·preferred | ||
| 312 | ······to·avoid·the·overhead·of·threading·and·the·large·number·of·locks·involved | ||
| 313 | ······and·preferred·a·event·driven·architecture·with·our·own·scheduling·of | ||
| 314 | ······events.·An·unpleasant·consequence·of·such·an·approach·is·that·long | ||
| 315 | ······lasting·tasks·must·be·split·to·more·parts·linked·by·special·events·or | ||
| 316 | ······timers·to·make·the·CPU·available·for·other·tasks·as·well. | ||
| 317 | *****·1.3·Architecture·***** | ||
| 318 | The·requirements·set·above·have·lead·to·a·simple·modular·architecture | ||
| 319 | containing·the·following·types·of·modules: | ||
| 320 | ··Core·modules | ||
| 321 | ······implement·the·core·functions·of·BIRD:·taking·care·of·routing·tables, | ||
| 322 | ······keeping·protocol·status,·interacting·with·the·user·using·the·Command-Line | ||
| 323 | ······Interface·(to·be·called·CLI·in·the·rest·of·this·document)·etc. | ||
| 324 | ··Library·modules | ||
| 325 | ······form·a·large·set·of·various·library·functions·implementing·several·data | ||
| 326 | ······abstractions,·utility·functions·and·also·functions·which·are·a·part·of | ||
| 327 | ······the·standard·libraries·on·some·systems,·but·missing·on·other·ones. | ||
| 328 | ··Resource·management·modules | ||
| 329 | ······take·care·of·resources,·their·allocation·and·automatic·freeing·when·the | ||
| 330 | ······module·having·requested·shuts·itself·down. | ||
| 331 | ··Configuration·modules | ||
| 332 | ······are·fragments·of·lexical·analyzer,·grammar·rules·and·the·corresponding | ||
| 333 | ······snippets·of·C·code.·For·each·group·of·code·modules·(core,·each·protocol, | ||
| 334 | ······filters)·there·exist·a·configuration·module·taking·care·of·all·the | ||
| 335 | ······related·configuration·stuff. | ||
| 336 | ··The·filter | ||
| 337 | ······implements·the·route·filtering·language. | ||
| 338 | ··Protocol·modules | ||
| 339 | ······implement·the·individual·routing·protocols. | ||
| 340 | ··System-dependent·modules | ||
| 341 | ······implement·the·interface·between·BIRD·and·specific·operating·systems. | ||
| 342 | ··The·client | ||
| 343 | ······is·a·simple·program·providing·an·easy,·though·friendly·interface·to·the | ||
| 344 | ······CLI. | ||
| 345 | *****·1.4·Implementation·***** | ||
| 346 | BIRD·has·been·written·in·GNU·C.·We've·considered·using·C++,·but·we've·preferred | ||
| 347 | the·simplicity·and·straightforward·nature·of·C·which·gives·us·fine·control·over | ||
| 348 | all·implementation·details·and·on·the·other·hand·enough·instruments·to·build | ||
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| 10 | <H2>Ondrej·Filip·<I><feela@network.cz></I>, | 10 | <H2>Ondrej·Filip·<I><feela@network.cz></I>, |
| 11 | Pavel·Machek·<I><pavel@ucw.cz></I>, | 11 | Pavel·Machek·<I><pavel@ucw.cz></I>, |
| 12 | Martin·Mares·<I><mj@ucw.cz></I>, | 12 | Martin·Mares·<I><mj@ucw.cz></I>, |
| 13 | Ondrej·Zajicek·<I><santiago@crfreenet.org></I></H2> | 13 | Ondrej·Zajicek·<I><santiago@crfreenet.org></I></H2> |
| 14 | <P><HR> | 14 | <P><HR> |
| 15 | <EM>This·document·contains·programmer's·documentation·for·the·BIRD·Internet·Routing·Daemon·project.</EM> | 15 | <EM>This·document·contains·programmer's·documentation·for·the·BIRD·Internet·Routing·Daemon·project.</EM> |
| 16 | <HR> | 16 | <HR> |
| 17 | <H2><A·NAME="s1">1.·BIRD·Design</A></H2> | ||
| 18 | <H2><A·NAME="ss1.1">1.1·Introduction</A> | ||
| 19 | </H2> | ||
| 20 | <P>This·document·describes·the·internal·workings·of·BIRD,·its·architecture, | ||
| 21 | design·decisions·and·rationale·behind·them.·It·also·contains·documentation·on | ||
| 22 | all·the·essential·components·of·the·system·and·their·interfaces. | ||
| 23 | <P> | ||
| 24 | <P>Routing·daemons·are·complicated·things·which·need·to·act·in·real·time | ||
| 25 | to·complex·sequences·of·external·events,·respond·correctly·even·to·the·most·erroneous·behavior | ||
| 26 | of·their·environment·and·still·handle·enormous·amount·of·data·with·reasonable | ||
| 27 | speed.·Due·to·all·of·this,·their·design·is·very·tricky·as·one·needs·to·carefully | ||
| 28 | balance·between·efficiency,·stability·and·(last,·but·not·least)·simplicity·of | ||
| 29 | the·program·and·it·would·be·possible·to·write·literally·hundreds·of·pages·about | ||
| 30 | all·of·these·issues.·In·accordance·to·the·famous·quote·of·Anton·Chekhov·"Shortness | ||
| 31 | is·a·sister·of·talent",·we've·tried·to·write·a·much·shorter·document·highlighting | ||
| 32 | the·most·important·stuff·and·leaving·the·boring·technical·details·better·explained | ||
| 33 | by·the·program·source·itself·together·with·comments·contained·therein. | ||
| 34 | <P> | ||
| 35 | <H2><A·NAME="ss1.2">1.2·Design·goals</A> | ||
| 36 | </H2> | ||
| 37 | <P>When·planning·the·architecture·of·BIRD,·we've·taken·a·close·look·at·the·other·existing·routing | ||
| 38 | daemons·and·also·at·some·of·the·operating·systems·used·on·dedicated·routers,·gathered·all·important | ||
| 39 | features·and·added·lots·of·new·ones·to·overcome·their·shortcomings·and·to·better·match·the·requirements | ||
| 40 | of·routing·in·today's·Internet:·IPv6,·policy·routing,·route·filtering·and·so·on.·From·this | ||
| 41 | planning,·the·following·set·of·design·goals·has·arisen: | ||
| 42 | <P> | ||
| 43 | <UL> | ||
| 44 | <LI><I>Support·all·the·standard·routing·protocols·and·make·it·easy·to·add·new·ones.</I> | ||
| 45 | This·leads·to·modularity·and·clean·separation·between·the·core·and·the·protocols. | ||
| 46 | </LI> | ||
| 47 | <LI><I>Support·both·IPv4·and·IPv6·in·the·same·source·tree,·re-using·most·of·the·code.</I> | ||
| 48 | This·leads·to·abstraction·of·IP·addresses·and·operations·on·them. | ||
| 49 | </LI> | ||
| 50 | <LI><I>Minimize·OS·dependent·code·to·make·porting·as·easy·as·possible.</I> | ||
| 51 | Unfortunately,·such·code·cannot·be·avoided·at·all·as·the·details·of·communication·with | ||
| 52 | the·IP·stack·differ·from·OS·to·OS·and·they·often·vary·even·between·different | ||
| 53 | versions·of·the·same·OS.·But·we·can·isolate·such·code·in·special·modules·and | ||
| 54 | do·the·porting·by·changing·or·replacing·just·these·modules. | ||
| 55 | Also,·don't·rely·on·specific·features·of·various·operating·systems,·but·be·able | ||
| 56 | to·make·use·of·them·if·they·are·available. | ||
| 57 | </LI> | ||
| 58 | <LI><I>Allow·multiple·routing·tables.</I> | ||
| 59 | Easily·solvable·by·abstracting·out·routing·tables·and·the·corresponding·operations. | ||
| 60 | </LI> | ||
| 61 | <LI><I>Offer·powerful·route·filtering.</I> | ||
| 62 | There·already·were·several·attempts·to·incorporate·route·filters·to·a·dynamic·router, | ||
| 63 | but·most·of·them·have·used·simple·sequences·of·filtering·rules·which·were·very·inflexible | ||
| 64 | and·hard·to·use·for·non-trivial·filters.·We've·decided·to·employ·a·simple·loop-free | ||
| 65 | programming·language·having·access·to·all·the·route·attributes·and·being·able·to | ||
| 66 | modify·the·most·of·them. | ||
| 67 | </LI> | ||
| 68 | <LI><I>Support·easy·configuration·and·re-configuration.</I> | ||
| 69 | Most·routers·use·a·simple·configuration·language·designed·ad·hoc·with·no·structure·at·all | ||
| 70 | and·allow·online·changes·of·configuration·by·using·their·command-line·interface,·thus | ||
| 71 | any·complex·re-configurations·are·hard·to·achieve·without·replacing·the·configuration | ||
| 72 | file·and·restarting·the·whole·router.·We've·decided·to·use·a·more·general·approach:·to | ||
| 73 | have·a·configuration·defined·in·a·context-free·language·with·blocks·and·nesting,·to | ||
| 74 | perform·all·configuration·changes·by·editing·the·configuration·file,·but·to·be·able | ||
| 75 | to·read·the·new·configuration·and·smoothly·adapt·to·it·without·disturbing·parts·of | ||
| 76 | the·routing·process·which·are·not·affected·by·the·change. | ||
| 77 | </LI> | ||
| 78 | <LI><I>Be·able·to·be·controlled·online.</I> | ||
| 79 | In·addition·to·the·online·reconfiguration,·a·routing·daemon·should·be·able·to·communicate | ||
| 80 | with·the·user·and·with·many·other·programs·(primarily·scripts·used·for·network·maintenance) | ||
| 81 | in·order·to·make·it·possible·to·inspect·contents·of·routing·tables,·status·of·all | ||
| 82 | routing·protocols·and·also·to·control·their·behavior·(disable,·enable·or·reset·a·protocol·without·restarting·all·the·others).·To·achieve | ||
| 83 | this,·we·implement·a·simple·command-line·protocol·based·on·those·used·by·FTP·and·SMTP | ||
| 84 | (that·is·textual·commands·and·textual·replies·accompanied·by·a·numeric·code·which·makes | ||
| 85 | them·both·readable·to·a·human·and·easy·to·recognize·in·software). | ||
| 86 | </LI> | ||
| 87 | <LI><I>Respond·to·all·events·in·real·time.</I> | ||
| 88 | A·typical·solution·to·this·problem·is·to·use·lots·of·threads·to·separate·the·workings | ||
| 89 | of·all·the·routing·protocols·and·also·of·the·user·interface·parts·and·to·hope·that | ||
| 90 | the·scheduler·will·assign·time·to·them·in·a·fair·enough·manner.·This·is·surely·a·good | ||
| 91 | solution,·but·we·have·resisted·the·temptation·and·preferred·to·avoid·the·overhead·of·threading | ||
| 92 | and·the·large·number·of·locks·involved·and·preferred·a·event·driven·architecture·with | ||
| 93 | our·own·scheduling·of·events.·An·unpleasant·consequence·of·such·an·approach | ||
| 94 | is·that·long·lasting·tasks·must·be·split·to·more·parts·linked·by·special | ||
| 95 | events·or·timers·to·make·the·CPU·available·for·other·tasks·as·well. | ||
| 96 | </LI> | ||
| 97 | </UL> | ||
| 98 | <P> | ||
| 99 | <H2><A·NAME="ss1.3">1.3·Architecture</A> | ||
| 100 | </H2> | ||
| 101 | <P>The·requirements·set·above·have·lead·to·a·simple·modular·architecture·containing | ||
| 102 | the·following·types·of·modules: | ||
| 103 | <P> | ||
| 104 | <DL> | ||
| 105 | <P> | ||
| 106 | <DT>Core·modules<DD><P>implement·the·core·functions·of·BIRD:·taking·care | ||
| 107 | of·routing·tables,·keeping·protocol·status,·interacting·with·the·user·using | ||
| 108 | the·Command-Line·Interface·(to·be·called·CLI·in·the·rest·of·this·document) | ||
| 109 | etc. | ||
| 110 | <P> | ||
| 111 | <DT>Library·modules<DD><P>form·a·large·set·of·various·library·functions | ||
| 112 | implementing·several·data·abstractions,·utility·functions·and·also·functions | ||
| 113 | which·are·a·part·of·the·standard·libraries·on·some·systems,·but·missing·on·other | ||
| 114 | ones. | ||
| 115 | <P> | ||
| 116 | <DT>Resource·management·modules<DD><P>take·care·of·resources,·their·allocation | ||
| 117 | and·automatic·freeing·when·the·module·having·requested·shuts·itself·down. | ||
| 118 | <P> | ||
| 119 | <DT>Configuration·modules<DD><P>are·fragments·of·lexical·analyzer, | ||
| 120 | grammar·rules·and·the·corresponding·snippets·of·C·code.·For·each·group | ||
| 121 | of·code·modules·(core,·each·protocol,·filters)·there·exist·a·configuration | ||
| 122 | module·taking·care·of·all·the·related·configuration·stuff. | ||
| 123 | <P> | ||
| 124 | <DT>The·filter<DD><P>implements·the·route·filtering·language. | ||
| 125 | <P> | ||
| 126 | <DT>Protocol·modules<DD><P>implement·the·individual·routing·protocols. | ||
| 127 | <P> | ||
| 128 | <DT>System-dependent·modules<DD><P>implement·the·interface·between·BIRD | ||
| 129 | and·specific·operating·systems. | ||
| 130 | <P> | ||
| 131 | <DT>The·client<DD><P>is·a·simple·program·providing·an·easy,·though·friendly | ||
| 132 | interface·to·the·CLI. | ||
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| Offset 1, 14 lines modified | Offset 1, 3693 lines modified | ||
| 1 | ******·BIRD·Programmer's·Documentation·****** | 1 | ******·BIRD·Programmer's·Documentation·****** |
| 2 | *****·Ondrej·Filip·<feela@network.cz>,·Pavel·Machek·<pavel@ucw.cz>,·Martin | 2 | *****·Ondrej·Filip·<feela@network.cz>,·Pavel·Machek·<pavel@ucw.cz>,·Martin |
| 3 | Mares·<mj@ucw.cz>,·Ondrej·Zajicek·<santiago@crfreenet.org>·***** | 3 | Mares·<mj@ucw.cz>,·Ondrej·Zajicek·<santiago@crfreenet.org>·***** |
| 4 | =============================================================================== | 4 | =============================================================================== |
| 5 | This·document·contains·programmer's·documentation·for·the·BIRD·Internet·Routing | 5 | This·document·contains·programmer's·documentation·for·the·BIRD·Internet·Routing |
| 6 | Daemon·project. | 6 | Daemon·project. |
| 7 | =============================================================================== | 7 | =============================================================================== |
| 8 | *****·1.·BIRD·Design·***** | ||
| 9 | *****·1.1·Introduction·***** | ||
| 10 | This·document·describes·the·internal·workings·of·BIRD,·its·architecture,·design | ||
| 11 | decisions·and·rationale·behind·them.·It·also·contains·documentation·on·all·the | ||
| 12 | essential·components·of·the·system·and·their·interfaces. | ||
| 13 | Routing·daemons·are·complicated·things·which·need·to·act·in·real·time·to | ||
| 14 | complex·sequences·of·external·events,·respond·correctly·even·to·the·most | ||
| 15 | erroneous·behavior·of·their·environment·and·still·handle·enormous·amount·of | ||
| 16 | data·with·reasonable·speed.·Due·to·all·of·this,·their·design·is·very·tricky·as | ||
| 17 | one·needs·to·carefully·balance·between·efficiency,·stability·and·(last,·but·not | ||
| 18 | least)·simplicity·of·the·program·and·it·would·be·possible·to·write·literally | ||
| 19 | hundreds·of·pages·about·all·of·these·issues.·In·accordance·to·the·famous·quote | ||
| 20 | of·Anton·Chekhov·"Shortness·is·a·sister·of·talent",·we've·tried·to·write·a·much | ||
| 21 | shorter·document·highlighting·the·most·important·stuff·and·leaving·the·boring | ||
| 22 | technical·details·better·explained·by·the·program·source·itself·together·with | ||
| 23 | comments·contained·therein. | ||
| 24 | *****·1.2·Design·goals·***** | ||
| 25 | When·planning·the·architecture·of·BIRD,·we've·taken·a·close·look·at·the·other | ||
| 26 | existing·routing·daemons·and·also·at·some·of·the·operating·systems·used·on | ||
| 27 | dedicated·routers,·gathered·all·important·features·and·added·lots·of·new·ones | ||
| 28 | to·overcome·their·shortcomings·and·to·better·match·the·requirements·of·routing | ||
| 29 | in·today's·Internet:·IPv6,·policy·routing,·route·filtering·and·so·on.·From·this | ||
| 30 | planning,·the·following·set·of·design·goals·has·arisen: | ||
| 31 | ····*·Support·all·the·standard·routing·protocols·and·make·it·easy·to·add·new | ||
| 32 | ······ones.·This·leads·to·modularity·and·clean·separation·between·the·core·and | ||
| 33 | ······the·protocols. | ||
| 34 | ····*·Support·both·IPv4·and·IPv6·in·the·same·source·tree,·re-using·most·of·the | ||
| 35 | ······code.·This·leads·to·abstraction·of·IP·addresses·and·operations·on·them. | ||
| 36 | ····*·Minimize·OS·dependent·code·to·make·porting·as·easy·as·possible. | ||
| 37 | ······Unfortunately,·such·code·cannot·be·avoided·at·all·as·the·details·of | ||
| 38 | ······communication·with·the·IP·stack·differ·from·OS·to·OS·and·they·often·vary | ||
| 39 | ······even·between·different·versions·of·the·same·OS.·But·we·can·isolate·such | ||
| 40 | ······code·in·special·modules·and·do·the·porting·by·changing·or·replacing·just | ||
| 41 | ······these·modules.·Also,·don't·rely·on·specific·features·of·various·operating | ||
| 42 | ······systems,·but·be·able·to·make·use·of·them·if·they·are·available. | ||
| 43 | ····*·Allow·multiple·routing·tables.·Easily·solvable·by·abstracting·out·routing | ||
| 44 | ······tables·and·the·corresponding·operations. | ||
| 45 | ····*·Offer·powerful·route·filtering.·There·already·were·several·attempts·to | ||
| 46 | ······incorporate·route·filters·to·a·dynamic·router,·but·most·of·them·have·used | ||
| 47 | ······simple·sequences·of·filtering·rules·which·were·very·inflexible·and·hard | ||
| 48 | ······to·use·for·non-trivial·filters.·We've·decided·to·employ·a·simple·loop- | ||
| 49 | ······free·programming·language·having·access·to·all·the·route·attributes·and | ||
| 50 | ······being·able·to·modify·the·most·of·them. | ||
| 51 | ····*·Support·easy·configuration·and·re-configuration.·Most·routers·use·a | ||
| 52 | ······simple·configuration·language·designed·ad·hoc·with·no·structure·at·all | ||
| 53 | ······and·allow·online·changes·of·configuration·by·using·their·command-line | ||
| 54 | ······interface,·thus·any·complex·re-configurations·are·hard·to·achieve·without | ||
| 55 | ······replacing·the·configuration·file·and·restarting·the·whole·router.·We've | ||
| 56 | ······decided·to·use·a·more·general·approach:·to·have·a·configuration·defined | ||
| 57 | ······in·a·context-free·language·with·blocks·and·nesting,·to·perform·all | ||
| 58 | ······configuration·changes·by·editing·the·configuration·file,·but·to·be·able | ||
| 59 | ······to·read·the·new·configuration·and·smoothly·adapt·to·it·without·disturbing | ||
| 60 | ······parts·of·the·routing·process·which·are·not·affected·by·the·change. | ||
| 61 | ····*·Be·able·to·be·controlled·online.·In·addition·to·the·online | ||
| 62 | ······reconfiguration,·a·routing·daemon·should·be·able·to·communicate·with·the | ||
| 63 | ······user·and·with·many·other·programs·(primarily·scripts·used·for·network | ||
| 64 | ······maintenance)·in·order·to·make·it·possible·to·inspect·contents·of·routing | ||
| 65 | ······tables,·status·of·all·routing·protocols·and·also·to·control·their | ||
| 66 | ······behavior·(disable,·enable·or·reset·a·protocol·without·restarting·all·the | ||
| 67 | ······others).·To·achieve·this,·we·implement·a·simple·command-line·protocol | ||
| 68 | ······based·on·those·used·by·FTP·and·SMTP·(that·is·textual·commands·and·textual | ||
| 69 | ······replies·accompanied·by·a·numeric·code·which·makes·them·both·readable·to·a | ||
| 70 | ······human·and·easy·to·recognize·in·software). | ||
| 71 | ····*·Respond·to·all·events·in·real·time.·A·typical·solution·to·this·problem·is | ||
| 72 | ······to·use·lots·of·threads·to·separate·the·workings·of·all·the·routing | ||
| 73 | ······protocols·and·also·of·the·user·interface·parts·and·to·hope·that·the | ||
| 74 | ······scheduler·will·assign·time·to·them·in·a·fair·enough·manner.·This·is | ||
| 75 | ······surely·a·good·solution,·but·we·have·resisted·the·temptation·and·preferred | ||
| 76 | ······to·avoid·the·overhead·of·threading·and·the·large·number·of·locks·involved | ||
| 77 | ······and·preferred·a·event·driven·architecture·with·our·own·scheduling·of | ||
| 78 | ······events.·An·unpleasant·consequence·of·such·an·approach·is·that·long | ||
| 79 | ······lasting·tasks·must·be·split·to·more·parts·linked·by·special·events·or | ||
| 80 | ······timers·to·make·the·CPU·available·for·other·tasks·as·well. | ||
| 81 | *****·1.3·Architecture·***** | ||
| 82 | The·requirements·set·above·have·lead·to·a·simple·modular·architecture | ||
| 83 | containing·the·following·types·of·modules: | ||
| 84 | ··Core·modules | ||
| 85 | ······implement·the·core·functions·of·BIRD:·taking·care·of·routing·tables, | ||
| 86 | ······keeping·protocol·status,·interacting·with·the·user·using·the·Command-Line | ||
| 87 | ······Interface·(to·be·called·CLI·in·the·rest·of·this·document)·etc. | ||
| 88 | ··Library·modules | ||
| 89 | ······form·a·large·set·of·various·library·functions·implementing·several·data | ||
| 90 | ······abstractions,·utility·functions·and·also·functions·which·are·a·part·of | ||
| 91 | ······the·standard·libraries·on·some·systems,·but·missing·on·other·ones. | ||
| 92 | ··Resource·management·modules | ||
| 93 | ······take·care·of·resources,·their·allocation·and·automatic·freeing·when·the | ||
| 94 | ······module·having·requested·shuts·itself·down. | ||
| 95 | ··Configuration·modules | ||
| 96 | ······are·fragments·of·lexical·analyzer,·grammar·rules·and·the·corresponding | ||
| 97 | ······snippets·of·C·code.·For·each·group·of·code·modules·(core,·each·protocol, | ||
| 98 | ······filters)·there·exist·a·configuration·module·taking·care·of·all·the | ||
| 99 | ······related·configuration·stuff. | ||
| 100 | ··The·filter | ||
| 101 | ······implements·the·route·filtering·language. | ||
| 102 | ··Protocol·modules | ||
| 103 | ······implement·the·individual·routing·protocols. | ||
| 104 | ··System-dependent·modules | ||
| 105 | ······implement·the·interface·between·BIRD·and·specific·operating·systems. | ||
| 106 | ··The·client | ||
| 107 | ······is·a·simple·program·providing·an·easy,·though·friendly·interface·to·the | ||
| 108 | ······CLI. | ||
| 109 | *****·1.4·Implementation·***** | ||
| 110 | BIRD·has·been·written·in·GNU·C.·We've·considered·using·C++,·but·we've·preferred | ||
| 111 | the·simplicity·and·straightforward·nature·of·C·which·gives·us·fine·control·over | ||
| 112 | all·implementation·details·and·on·the·other·hand·enough·instruments·to·build | ||
| 113 | the·abstractions·we·need. | ||
| 114 | The·modules·are·statically·linked·to·produce·a·single·executable·file·(except | ||
| 115 | for·the·client·which·stands·on·its·own). | ||
| 116 | The·building·process·is·controlled·by·a·set·of·Makefiles·for·GNU·Make, | ||
| 117 | intermixed·with·several·Perl·and·shell·scripts. | ||
| 118 | The·initial·configuration·of·the·daemon,·detection·of·system·features·and | ||
| 119 | selection·of·the·right·modules·to·include·for·the·particular·OS·and·the·set·of | ||
| 120 | protocols·the·user·has·chosen·is·performed·by·a·configure·script·generated·by | ||
| 121 | GNU·Autoconf. | ||
| 122 | The·parser·of·the·configuration·is·generated·by·the·GNU·Bison. | ||
| 123 | The·documentation·is·generated·using·SGMLtools·with·our·own·DTD·and·mapping | ||
| 124 | rules·which·produce·both·an·online·version·in·HTML·and·a·neatly·formatted·one | ||
| 125 | for·printing·(first·converted·from·SGML·to·LaTeX·and·then·processed·by·TeX·and | ||
| 126 | dvips·to·get·a·PostScript·file). | ||
| 127 | The·comments·from·C·sources·which·form·a·part·of·the·programmer's·documentation | ||
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