Magazine - 1000 BiT

7 .ncn\.orlt. The solution is to allo\\* important picccs oti~iformntion to be Icarncd and the s!-stcln to autocolifigureitself using this data. IPv6 autoconfigurationc~~compasscs the ti)llo\vinb r ~tcnis: 'Router discoveryOn-link pcti s disco\.cr!*Intcrhcc ntrributc configurationStateless ;iddress config~~rationSt~tcf~~l address config~~r.itionTllc mccl.lnnisn~ for dcl.i\~cring this infol-rn'ltioll tothe Ilosts is rlic router advertise~nie~nt (TW) pacltct ofthe Nciglibor l)isco\~cry Protocol. In tlic follo\\,ingsections, \\,c describe the methods \\~c dc\,clopcd toprocc~stlncsc pnckcts and i~pdate the systc~ii.Host Autoconfiguration DaemonTo p~)ccss tlicsc RAs, \\.c designed n host d.icmoncalled ~ldbhostd, \\.hich resides in the application spaceof the lligitnl UNIS operating systc~l~. Wc dctcrmincdt11at a LISCI--I~~O~C daemo~~ \vas the most efficientto implement I Pv6 autoconfig~~ration fc)r the fi)llo\\.-ing reasons:A user-mode dacmon \vould avoid ler~icl bloat.M.lintcnn~lcc and cstensibilin~ \\rould be c,lsier.The hl~iction is not performance critical.Thc autoconfiguratio~i processing is implcmcntcd.IS a single esccutahlc image, as a coliesi\.e scr oftightlycoupled modules. 'l'hc dnerlion currently is dcsigncclas a single-threaded application that i~scs a dispatchmechanism to call cacli specialized fiunction niodulc inturn. W \\.ill csnminc the idca of hn\,ing this dacmonrun as a mulritlircadcd application in the hlturc.'l'lic ndbhosrd dacnnon comnnunicatcs \\.it11 thenen\.ork suhs\~ste~ni in tlnc Iwrnel through multipletcchniqucs. Fiprc 10 sI1on.s the autoco~ifigi~~-nrion~x-occssiing ~inodulcs. Tile Inn. socket interfncc is uscci torccci\.c IMs, and J/O control messages (ioctls) arc usedto mnnipulnte Iterncl data structures. Also, tlic routiugtnblc is updated ns neccssar!; b!, mews of .J. ran. socketintcrfiicc to the I'F-ROUTE protocol hmily.W dcsig~led the J1%6 ran- socket's intcrfilcc \\.it11the abilih to pass only specific ICMP\,6 messages ton user and to filter extraneous packets or protocols.1 lie nd6liostd daemon sets n socket option to rccci\pco~~l!. neighbor discovery Rgs. It then crccutcs ;I ciispatchrolltine that polls the ra\v socltct, a\\,aitingpnckcts. Wen data is available on the socltct, the dncmondctcrmincs the characteristics of the message,crc~tes ;I data structure to contain it, 2nd calls the ncccs~nr!~f~nctions to perform autoconfigul-ation. ?'hcdisp;~tcli ~iiotiulc, in addition to polling socltct dcscriptors,S L I ~ P O J'lcccssary ~ ~ S timer Inanngcmcllt filnctionssucl~ as creation, deletion, rind expiration. Figurc 11slio\\,s tlic npplici~tion daemon design center.Kernel Interface Data StructuresIn many \\ays, the data link interface is tlic fi>cus ofI1+6 nutocontiguration support. The kernel clat~ structuresk)r Ih4 interfaces arc not sufficient to jrnplcmc~~tthe ncccssar! IP1.6 tiinctions. We designed and implcmcntcdnc\\. intesfiice data structures that encapsulatedthe existing I h.4 structures. This allo\\-cd us to avoid ;Ircconnpilarion of the existing data link dri\.crs on the13igitnl UNIS operating system. In the filturc, 1j.c \\.illattempt LI dcsig-11 ill \\rhich thc intcrEicc StrLIctiIrcsI1'\,4 and I l'v6 arc completely integrated.As slio\\~n in Figire 12, \\Ie designed an in6-itiictsrrucrurc to support each data linli typc (c.g.,t;,thcrnct, I'PI', loopback) 2nd used the csistiligifiict structures to point to thosc link in[-erf,lccs. Tlicin6-ifiict lias its oun in6-ifaddr structure k)l. cncliII'vO address configured in the dntn structurein6-IocalaJJr. Wc also defined rlic in6-router structureto support each routcr availnblc For the implcmentation.Thc in6-router structilrc spccitics theintc~.Eicc of the router, neighbor cache route, ;indthe 1 P1.6 address of the router.ION-LINK INTERFACE STATELESS STATEFULROUTER PREFIX ATTRIBUTE ADDRESS ADDRESSDISCOVERY DISCOVERY PROCESSING CONFIGURATION CONFIGURATION (DHCPVG)t t t t tIPV6 SOURCEADDRESS DEFAULTROUTERLIFETIMEPREFIX OPTIONS:ON-LINK PREFIXPREFIX LENGTHVALID LIFETIMERECEIVING INTERFACEHOP LIMITREACHABLE TIMERETRANSMIT TIMELINK MTUI I I IROUTER ADVERTISEMENTPREFIX OPTIONS:ADDRESS PREFIXPREFIX LENGTHVALID LIFETIMEPREFERRED LIFETIMEMANAGED BIT, OTHERCONFIGURATION BITFigure 10Autoconfg~~rntion Processing ~ModuIes