Magazine - 1000 BiT

AUTOCONFIGURATIONPROCESSINGUSER SPACEKERNEL SPACEIOCTLsSIOCIPVGADDRTRSIOCIPVGDELRTRSIOCIPVGIFINITSIOCIPVGAIFADDRSIOCIPVGSIFATTRAvSIOCIPVGGIFATTRSIOCIPVGMIFADDRSIOCIPVGGIFADDRSIOCIPVGDIFADDRIPV6 INTERFACE CONTROL MODULEADDRESSES AND STATEON-LINK PREFIXESROUTE ATTRIBUTESDATA LINK ATTRIBUTESFigure 13IntcrLicc Attribute Updatesand the Iternel data structures k)r routcr intbrrnationarc upd.ltcd. The routcr lifctimc ficld in the 1WdcfincsIio\\, long this router ma), bc used as a defa~~lt routel..The ndbliostci daemon first updates the intcrf~ccattributes. A tinier is sct ~~sitig the appropriate routinefrom the ciispatcli module. When the timer expires,the delete dcKx~lt routcr routine is callcd, and theroutcr is deleted from the routing table. The daemonmust also be able to dclctc the rourcl- if it recei\,es an1W \\,it11 a zcro lifetime \7;1lue, \\,liicli can occur \\,lien anode is acting as n routcr b~lt is rcsct to be ~1 llost.On-link PrefixesAn on-link prefix in TI36 def nes a subnet a11d is typicallyconfigured on a routcr for a specific link by thencnvork administrator. The routcr tlicn ad\fcrtiscs thisprcfi s to all nodcs connccteci to that linl< as a prctisoption, appended to an IW. A pretis option dctincs ,Isinglc prefix only, but an 1W may contain niore th;inone such option. As sho\vn in Figurc 8, tlie prefixoption pro\.ides tlie fbllo\ving information:Prcfs lengthLink- or L-bit, \\~liiclis sct if tlic prcfis is dircctl!~rcaclablc on link (i.c., a neighbor)Autono~nous- or A- bit, \\rhicli is set if the prcfis canbe used for statclcss address conf g~~rationThe length of time the prefix is \didThe dac111on adds the prcfis to tl~c routing table.Then a timer ro~ttinc is c:lllcil fro111 the disparcll mod-IIIC JI~LI ib kc1 t;)r thc ~ imc tllr k>r,cti,y ~z \.,)lid. W~ICIIdispatch routit~e calls the delctc on-link prefix nlodulc,the prefis is dcletcd fion~ the routing tablc. A prcfisc.111 .IIXJ bc dclctcd I\.I~CIL ,I I ~CM K,\ ~)rcsc'~~ts tlx profix\\.ith a lifetime of zero. In that c,lsc, the on-linkprefix modulc \\.ill stop the timer routine and deleteIIIC prclii II*OIII t11c ro11i111g I.II>Ic.111~Address ConfigurationAddress configuration is one of thc nc\\. paraciigmsthat InLlst bc supported in I11\,6. '1'1\~o configurationmethods, stateless and statcftll, are pro\ridcd to autoconfigureaddresses for a ]lost. The M-bit flag in an Kiimessage determines \\.hich method to i~sc and inhrn~sa host. In addition, the othcl--bit (0-bit) flag is pro-\,idcd to configure other nct\vork parameters requiredfor the host's operation on thc nen\~orli \vIicn tliestatefill config~~ration is uscti.Adtircss autoconfigurntion in IPi.6 supports thc~bilig, to dynamicall), rcnumbcr a link or a colnplctcnetwork througll thc use of lifetimes specified in the1W message. The \did lifetime is the timc the addresshas bcfixc cspiration. When the timer expires, ;ill connectionsusing that addrcss arc dropped b!~ tlie ilnplemc~ltation,ancl no lie\\ conncctiolls arc permitted.The preferred lifetime is provided to inform an implc-~ncntation that an address is about to expire; it typicallyis set to a lo\\lcr \value than the valid lifctinic.When this tinlcr cspircs, the addrcss is said to enter thedcprec~ted state, at \\.hic11 point an iniplcn~entatio~i is~xr~iiittcd (as a config~rration option) to prc\,cnt nenJcomm~~nications using this ndclrcss as a source 01. dcstin~~tion.'l'liis niodcl is designed to pro\~ide net\\,orliad~ninistrators with control over the use of net\\ro~-kaddresses \\.itho~~t manual intcr\,ention ofeach host onthe ncn\rork. The stateless niodcl is intended for users\\rho do not necd tight co~itrol over address config-~u-ation; statcfi~l mechanisms \vill be used \\,here thc:wirni~li~ t(\ dc-Iei?:~re 2dclr(h