【正文】 liable!!!) 72 Jim Binkley why router/work LSA? ? if no DR, no LSA, routerlsa would include links to all routers on work ? remember: N might have many routers ? each router i would have a link to router j – j to i, etc. ? optimization: work LSA lists routers ? routers list works ... therefore N * 2, not N * N ? DR originates work LSA, all routers originate router LSA 73 Jim Binkley broadcast , therefore R(j), routerlsa, R(j) on Net(i) R(i), routerlsa, on Net(i), also DR, Net(i) has Routers i,j,k R(k) , on Net(i) Net(i) 74 Jim Binkley summary LSAs ?3,4,5 all deal with areas ?3 for area aggregation ?4,5 for routing info needed for routing domain external routes – 4 says how to get to ASBR – 5 says here is a route beyond the ASBR/s – keep in mind possible 1 ASBR 75 Jim Binkley multihomed routing domain ip dst X ASBRs r1 r2 type 4, metric X to r1 type 5, this way to ip dst X OSPF routing domain default route 76 Jim Binkley types of areas ?ordinary joe bob area (this is about stub areas really, so this is NOT a stub area) – non area 0 router CAN be ASBR ?stub area – no transit traffic, no virtual links – does not accept external LSA, no ASBRs – only one way out – consumes least resources ?not so stubby area (NSSA) 77 Jim Binkley NSSA not so stubby ?assume stubby, but one change ?type 7 NSSA lsa can be used to export NSSA internal routes ?type 7 has area scope ?translated at ABR to type 5 ?therefore can have limited ASBR capability within NSSA area 78 Jim Binkley why NSSA diagram? area 51 NSSA area area 0 ABR internal RIP cloud router generates type7 LSAs type 5 LSAs secondlevel area note: RIP router above is NSSAASBR note: you may or may not do type7 to type5 translation 79 Jim Binkley OSPF protocol ? OSPF uses IP direct, not on top of UDP, IP proto = 89 ether ip p=89 OSPF pkt hdr, etc. 80 Jim Binkley OSPF packet types ?all have mon 24 byte pkt header ?5 distinct pkt types – 1 hello, 2 database description, 3 link state request, 4 link state update, 5 link state ACK ?all but hello may be viewed as LSA lists – link state update is flooded – database description used in bringing up adjacencies ?LSA itself has its own structure 81 Jim Binkley mon OSPF protocol header (24 bytes) 64 bits of authentication version type pkt length router ID area ID IP checksum auth type 82 Jim Binkley pkt header fields ?router ID typically an IP address ?area ID area this packet belongs to ?checksum IP checksum for all bytes in packet, does not include authentication, may be absent for some authentication types if redundant 83 Jim Binkley hello packet ( type = 1 ) BDR HelloInterval Options Rtr Pri RouterDeadInterval DesignatedRouter mon pkt hdr = 24 bytes ... work mask 1 of N Neighbor IDs ... (variable length) 84 Jim Binkley a few hello details ? OSPF multicast addresses: – all SPF routers ( I speak OSPF ) – all DR routers – note is e 01:00:0e:00:00:05 ? bcast hello time 10 seconds ? bcast dead time 40 seconds ? IP addr (routerID) and priority used in DR election ? note if local OS can tell you link is down, use that else 2way exchange can tell us 85 Jim Binkley more details ?ip ttl = 1 ?dest ip = ?DR/BDR values, 0 means none yet ?Neighbor IDs are IP addresses 86 Jim Binkley DDescription packet ( type = 2 ) Advertising Router DD sequence number Link State Type Link State ID mon pkt hdr = 24 bytes ... Link State Sequence Number 0 0 options flag bits checksum age 1 of N L S A .h d r ... 87 Jim Binkley request packet ( type = 3 ) Link State ID Advertising Router mon pkt hdr = 24 bytes ... LS type more LSAS, specified by 3tuple (type, ID, advertising router) ... note: we do not specify instance, we assume we want most fresh LSA 88 Jim Binkley update packet ( type = 4 ) LSA 1 (with LSA hdr/body) LSA 2 mon pkt hdr = 24 bytes ... of LSAS more plete LSAS ... note: this is standard flooded LSA, LSAs are plete 89 Jim Binkley Link State ACK, type = 5 ?may be sent to allspfrouters or allDRrouters or unicast for that matter ?format similar to DD packet ?type 5, with OSPF hdr first ?followed by 1..N LSAs headers, which must include ACK’ed instance ?may be slightly delayed in hope that ACKs will be more cumulative ?may use unicast to fast ACK DUP LSA 90 Jim Binkley LSA formats, 1st global header LS sequence number LS age Options LS type Link State ID Advertising Router LS checksum length header followed by per LSA info this is just an LSA, not a OSPF packet 91 Jim Binkley LSA header details ? key for LSA is (type, LS ID, advert router) ? types are 15 for basic LSAS (router/work, area summary, etc) – 5 for extended LSAs ? advert router, who originated LSA, note may or may not be same as Link State ID ? sequence number inc if LSA fresh ? LSA csum, fletcher (ISO), not IP ? length, includes LSA hdr, must fit in IP pkt ? age, 0 when 1st sent 92 Jim Binkley LSA link state ID ?associated with type ?type 1, originating router ID ?type 2, IP of i/f of work DR ?type 3, destination IP addr ?type 4, router ID of ASBR ?type 5, destination IP address 93 Jim Binkley routerLSA summary info ?router X – has separate links for interfaces – ., 3 links – each of which mentions a work – and metric on that work – all router interfaces must be mentioned 94 Jim Binkley