At 2:42 AM +0000 7/9/03, Priscilla Oppenheimer wrote: >Howard C. Berkowitz wrote: >> >> At 10:46 PM +0000 7/8/03, Zsombor Papp wrote: >> >The LSA will be fragmented at the IP layer. >> >> Do you know for certain this is what Cisco's implementation >> does? >> The OSPF code is aware of the MTU and can build OSPF packets >> for it. >> I don't think you're really going to simplify it by relieving >> it of >> the need to keep track of lengths. > >Can you think of a good way to test it in a lab??
Lots of loopback interfaces, with appropriate coding so they don't present as host routes, coupled with small MTUs. Part of the problem in testing will be that any practical configuration doesn't press the limits. IIRC, I ran some calculations a while back that imposed a more stringent limit on the number of routers per segment -- the number you could fit into a Hello packet was around 47, a smaller number than you could type 1 LSAs. > >The RFC says that dividing up the updates is recomended over letting IP do >the fragmentation and Cisco is generally good at doing things the >recommended way usually. The person that I know who wrote most of the _good_ OSPF code has left Cisco, but I'll hunt around on the IETF list and find out if I can find someone who knows definitively. There are a lot of things in OSPF (and, for that matter, BGP) that experience have taught are simply not good ideas in practice. You'll find the latest BGP draft (I think it's 21 now, if it's reached the editor) is both considerably different from the BGP route selection process described in RFC 1771, and is also much closer to what Cisco, Juniper, NextHop/gateD, and Zebra actually do. OSPF will continue to evolve. The classic Dijkstra algorithm won't continue to serve as faster convergence requirements are placed on OSPF. To the best of my knowledge, most implementations save at least some intermediate Dijkstra results, and the trend is to do at least some incremental updating before committing to a full SPF recomputation. > >Priscilla > > >> >> On the other hand, if you send a LSupdate that is at the MTU, >> the >> receiving router can immediately start checking and installing >> it in >> the LSDB, without waiting for fragments. This allows some >> concurrency >> between OSPF packet transmission and OSPF protocol processing. >> >> >At 11:39 AM 7/8/2003 +0000, hebn9999 wrote: >> >>layer 2 frame has a MTU of 1500 bytes. >> >> how does cisco router propagate router-lsa whose size >> exceed 1500 >> > >bytes(more than 122 links in one area)? Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=72050&t=72024 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
