3.5.2. Route mapRoute map l cc cng c trong cc logic if/then c th c p dng cho mt router. Cc route-map l cc cng c lp trnh c dng kim sot qu trnh redistribution, hin thc PBR, kim sot qu trnh NAT hoc hin thc BGP.Bn c th dng route-map cho cc mc ch sau y: kim sot qu trnh redistribution: cc route map cho php kim sot mt mc cao hn so vi cch dng distribution list. Route-map khng n thun ngn chn hay cho php mt mng ging nh distribute list m cn c kh nng gn metric cho nhng route b match. kim sot v thay i thng tin nh tuyn: cc route map c dng thay i thng tin nh tuyn bng cch gn gi tr metric cho cc route.nh ngha chnh sch trong PBR: cc route-map ra cc quyt nh da trn a ch ngun. Khi mt match c tm thy trong access-list, s c cc hnh ng tng ng. thm vo mc tinh t trong cu hnh NAT: cc route map nh ngha dy ca cc a ch public v a ch private. C cc lnh show gim st v kim tra hot ng ca NAT. hin thc BGP: mt trong nhng im mnh ca giao thc BGP l kh nng thc hin policy based routing. Cc thuc tnh trong BGP c dng nh hng n ng i cho traffic. Cc thuc tnh ny thng c hin thc dng route maps. Nu c mt match th p dng thuc tnh ny. Khi ny dng lnh set thc hin. Route map l phng thc ch yu c dng bi BGP nh ngha chnh sch nh tuyn BGP.Route map rt ging ACL. C hai thc hin tc v if/then, trong cc tiu ch c dng xc nh l packet c c cho php hoc t chi hay khng. S khc nhau c bn l route map c kh nng thc hin hnh ng thay i thuc tnh n cc gi d liu tha iu kin match. Trong mt ACL, tiu ch match l ngm nh, trong mt route map, l mtt kha. iu ny c ngha rng, nu mt gi tha vi mt tiu chun cho trong mt route map, mt vi hnh ng phi c thc hin thay i gi, trong khi accesslist ch n gin cho php hoc deny mt gi.Cc c im ca route map c tm tt trong danh sch sau:Mt route map c mt danh sch cc tiu ch v tiu chun chn la, c lit k vi pht biu mtch.- Mt route map c kh nng thay i cc gi hoc cc route b match bng cch dng lnh set.- Mt tp hp ca cc pht biu mch c cng tn c xem l cng mt route map- Route map s ngng x l ngay khi c mt match c thc hin, ging nh mt ACL.- Trong mt route map, mi pht biu c nh s th t v c th c son tho ring l.- S th t c dng ch ra th t trong cc iu kin c kim tra. Nh vy nu hai pht biu trong route map c tn l BESTTEST, mt pht biu c ch s l 5, mt pht biu c ch s l 15 th pht biu c ch s l 5 s c kim tra trc. Nu khng c mt pht biu match trong pht biu 5 th pht biu th 15 s c kim tra.- Route map c th dng cc IP access-list chun hoc m rng thit lp cc chnh sch nh tuyn.- Cc access-list m rng c th c dng ch ra tiu ch match da trn phn a ch ngun v a ch ch, ng dng, kiu giao thc, kiu dch v ToS v u tin.- Lnh match trong cc cu hnh route map c dng nh ngha iu kin phi kim tra.- Lnh set trong cu hnh route map c dng nh ngha hnh ng theo sau mt pht biu match.- Mt route map c th ch cc php AND v OR. Ging nh mt access-list, c mt pht biu ngm nh DENY cui mt route map. Hnh ng theo sau ca pht biu deny ny ty thuc route map c dng nh th no. hiu iu ny mt cch chnh xc, bn cn hiu chnh xc route map hot ng nh th no.

Danh sch sau y s gii thch logic ca hot ng route-map:

- Pht biu ca route map dng cho PBR c th c nh du nh l permit hoc deny- Ch nu pht biu c nh du nh permit v packet b match, lnh set mi c p dng.- Cc pht biu trong route-map s tng ng vi cc dng ca mt access-list. Ch ra mt iu kin match trong route map th cng tng t nh ch ra ngun v ch trong access list- Cc pht biu trong route map c so snh vi ng i ca gi xem c mt match no hay khng. Cc pht biu ny s c ln lt kim tra t trn xung di.- Mt pht biu match c th cha nhiu iu kin. t nht mt iu kin trong pht biu match phi l ng. y l php logic OR- M route-map c th cha nhiu pht biu match. Tt c cc pht biu match trong route map phi c xem xt l ng cho pht biu ca route map l match. iu kin ny gi l php logic AND.PBR p dng vo cc gi tin i vo hoc cc gi tin c to ra bi router. Khi mt gi tin nhn c trn mt interface c cu hnh PBR, gi tin s tri qua mt qui trnh nh sau:

- Nu c mt s kin match xy ra v hnh ng l cho php, gi tin s c route theo hnh ng c ch ra trong lnh set- Nu c mt s kin match xy ra v hnh ng l t chi gi tin th packet s khng c route theo chnh sch nhng s c nh tuyn nh bnh thng- Nu khng c match no v nu khng c thm on cu hnh no ch ra phi lm g trong tnh hung ny, mc nh gi tin s b deny, ngha l s chuyn v nh tuyn bnh thng. Qu trnh nh tuyn bnh thng s c th b loi b nu ta dng thm mt pht biu set nh tuyn packet v null0. Ni cch khc, y l cch loi b gi tin.http://www.vnpro.org/forum/forum/ccnp%C2%AE-v%C3%A0-ccdp%C2%AE/route-bsci/4842-c%C3%A2u-h%E1%BB%8Fi-v%E1%BB%81-%C4%91%E1%BA%B7c-t%C3%ADnh-c%E1%BB%A7a-route-map