You got here just before I did. I was just about to say that RFC 2328 overrides 2178.
""Kane, Christopher A."" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > The most frequently mismatched parameters relevant for OSPF > > > > configuration > > > > seem to be dead intervals & mtu sizes. > > > > > > OSPF doesn't care about MTU size. > > > > Uh, excuse me? Go read RFC 2178 (OSPF v2), section G.9: > > > > "When two neighboring routers have a different interface MTU for their > > common network segment, serious problems can ensue: large packets are > > prevented from being successfully transferred from one router > > to the other, > > impairing OSPF's flooding algorithm and possibly creating > > "black holes" for > > user data traffic. > > > > This memo [RFC2178] provides a fix for the interface MTU > > mismatch problem by > > advertising the interface MTU in Database Description > > packets. When a router > > receives a Database description packet advertising an MTU > > larger than the > > router can receive, the router drops the Database Description > > packet. This > > prevents an adjacency from forming, telling OSPF flooding and > > user data > > traffic to avoid the connection between the two routers. For more > > information, see Sections 10.6, 10.8, and A.3.3. > > > > Wow. The learning continues. I have never actually run into this problem. I > have checked the RFC. That's RFC 2328 by the way, it obsoletes RFC 2178. > > Indeed, its during the Database Describtion Packet exchange that the MTU > size is checked. The Database Description Packet format includes an > "Interface MTU" field. But, why wait until the DDP phase of the > neighbor/adjacency development? Why wouldn't this thing be a 'must match' > situation and be included in the Hello packet? I just config'd it in my lab > on a Point-to-Point and the neighbor state makes it to EXSTART and then > stops. The router with the smaller MTU size reports the following in it's > debug: > > Nbr x.x.x.x has larger interface MTU > > Only the router with the smaller MTU is upset by this. The router with the > interface that has the larger MTU makes no mention of any problems. > > Quick search on CCO shows that Cisco has a work around for this: > http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr > rp_r/1rfospf.htm#xtocid24 > > Again, learn something new everyday. Since MTU is never mentioned in the > Hello packet, I thought it didn't matter. > > Sorry about posting inaccurate information. I appreciate the feedback > pointing out my error. > > -chris Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=41767&t=41613 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
