At 12:56 AM 2/22/02, Chuck wrote: >BTW, it occurs to me that we have had this discussion before.
Yes, unfortunately. ;-) >There being >nothing in the routing table indicating IGRP or EIGRP hop counts, You can't see the hop count with show ip route perhaps, but the router certainly saves the info. Try the show ip eigrp command. It shows the hop count. >how does >(E)IGRP "know" the diameter of the network of which it is a member? It's basic distance vector processing. I receive a packet that lists a network as being 0 hops away. (The router listing it is directly connected.) From my point of view, then, the network is 1 hop away. When I advertise this network, I say that it is 1 hop away. My "downstream neighbor" considers it 2 hops away. When I add 1 to the hop count, if that causes the hop count to exceed "maximum hop count," then I trash the route and don't advertise it. > And why >would it "care"? ;-> Now, that's a good question. But why does any routing protocol care? >Maybe one of these days I'll daisy chain the routers in my lab, and set the >max hops to 4 and see what happens ;-> Just set the max to something smaller than the actual width. You'll see routes disappear. >Chuck > > >""Priscilla Oppenheimer"" wrote in message >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > At 08:05 PM 2/21/02, Chuck wrote: > > >to augment the other answers, the IP hop count is really the IP TTL >value. > > >It can never exceed 255 > > > > You're confusing two issues. > > > > Remember the router has two jobs: forwarding packets and learning the > > topology. Hop count has to do with the latter and affects what goes in the > > routing table. The IP TTL causes a router to drop a packet before > > forwarding if the TTL becomes zero. > > > > > > >EIGRP defaults to 100 hops, so I would expect that the routing packet IP >TTL > > >is set at 100 at that point. > > > > Routing packets only go to neighbors. The IP TTL should be set to one or > > two. This has nothing to do with hop count which will be later in the > > packet in the distance vectors. > > > > > > >Well ( checking the sniffer trace that Priscilla so thoughtfully supplied >a > > >couple of days ago ) I'm seeing the IP TTL as 2. Still, maybe there is an > > >adjustment made. After all, the (E)IGRP metric includes end to end >metrics. > > >hhmmm... ( looking over Priscilla's trace again ) way down there I see an > > >EIGRP hop count 0 line. > > > > The router was advertising a directly-connected network. > > > > > > >the IP TTL is still really the only thing that makes sense in terms of >the > > >way IP works. > > > > In terms of forwarding maybe. You better reconsider routing protocols > > though... > > > > Priscilla > > > > > > >Anyone? > > > > > >Chuck > > > > > >""Steven A. Ridder"" wrote in message > > >[EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > > > > Anyone know why there is a hop-count in EIGRP? It has a 1 byte value, > > but > > > > it doesn't limit the number of hops and it looks like routers don't >use > > it > > > > in their calculations. Why is it there? > > > > > > > > -- > > > > RFC 1149 Compliant. > > ________________________ > > > > Priscilla Oppenheimer > > http://www.priscilla.com ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=36252&t=36082 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
