> There should be a triggered update. It will list the unreachable network > with the largest possible delay. Could you check again? Perhaps in some > topologies, there would be no need to send a triggered update, but that > would be strange. I think you maybe just didn't recognize it as being a > triggered update.
I found the reason why there was no triggered updates : I used config like this : int eth0 ip address 10.0.0.1 255.0.0.0 ! router igrp 10 network 10.0.0.0 redistribute static ip route 1.0.0.0 255.0.0.0 Null0 ip route 2.0.0.0 255.0.0.0 Null0 I used route pointing to Null0 to simulate routes and when I suppressed a static route, there was no triggered update. But when I use "standard" config : int eth0 ip address 10.0.0.1 255.0.0.0 int eth1 ip address 11.0.0.1 255.0.0.0 ! router igrp 10 network 10.0.0.0 network 11.0.0.0 When I shutdown Eth1, there's a triggered update sent through eth0 ... So triggered updates are not generated when using redistribution (It worked fine with RIP, so I supposed that it should work with IGRP, but no). Thanks for your answers. -- Stephane LITKOWSKI Student in a French computer science school EPITA Telecom & Network specialization CCNA + CCNP EMail : [EMAIL PROTECTED] ""Priscilla Oppenheimer"" a icrit dans le message news: [EMAIL PROTECTED] > At 03:27 PM 4/17/02, Stephane LITKOWSKI wrote: > >Hi all, > > > >I have some questions about IGRP : > > > >- In an update, IGRP distinguish Subnets, AS Networks and outside-AS > >networks, when I take some traces, I can see that there's the number of each > >category and then all routing entries but I don't understand how IGRP know > >if the routing entry is Subnet, AS or outside AS. Distinguishing AS routes > >(major net) or subnets is not important (applying interface mask and > >comparing major networks can do distinction), but how IGRP knows if the > >routing entry is candidate default ? > > An IGRP update message has three portions: interior, system (meaning "this > autonomous system" but not interior), and exterior. (Sniffer uses slightly > different terminology.) The interior section is for routes to subnets for > the network on which the broadcast is being sent. > > Major networks (i.e. non-subnets) are put into the system portion of the > update message unless they are exterior. > > A network will be flagged as exterior if it was learned from another router > and the information arrived in the exterior portion of the update message. > > Exterior routes are also "candidate defaults." They are routes that go to > or through routers that are considered to be appropriate as defaults, to be > used when there is no explicit route to a destination. Cisco's > implementation chooses a default route by picking the exterior route with > the smallest metric. > > > >- I can see in traces that IP addresses are coded with just 3 bytes, so I > >think I cannot use subnets > 24 bits ... isn't it ? > > Not necessarily. Class C subnets could be greater than 24. > > With interior routes, a router can assume that the first octet is the same > as the first octet of the sending and receiving interfaces, so it can be > left out. Remember that IGRP is classful, so there's no way the prefix > boundary could be over to the left past the 8-bit boundary, so IGRP leaves > out the first 8 bits in interior (subnet) routes. Check your traces again. > I think you'll see that it's the first octet (not the last) that is left > out on interior routes. > > On system and exterior, which deal with major network numbers, the router > can leave out the last octet. > > > >- I can see different routing entry types, for example (traces done with NAI > >Sniffer Pro) : > > > >ROUTING ENTRY #1 > > IP Address = [172.16.1.0] > > ... > > > >ROUTING ENTRY #2 > > IP Address = [10.0.0.XX] > >... > > > >what does the XX mean ??? I can see in hexa dump that's 00 > > Which kind was this? System or exterior I would guess. Perhaps the XX just > means anything (wildcard). It's probably not actually in the hex dump, > since IGRP just uses 24 bits as you mentioned. Check for 0A 00 00, which > would be 10.0.0. > > > >- What is the utility of the hopcount ? preventing from loop like in RIP ? > > Yes, it prevents loops. I think if the router sees the hop count > increasing, it puts the route in holddown. > > >(so is the hop count incremented hop by hop ?) > > Yes. > > > >- I saw that Cisco implement trigger updates in IGRP, but on a Cisco 1603R > >with IOS 12.0(4)T, it don't seem to be implemented, when there's a change in > >topology, there's no trigger update. Does anyone experienced this problem ? > > There should be a triggered update. It will list the unreachable network > with the largest possible delay. Could you check again? Perhaps in some > topologies, there would be no need to send a triggered update, but that > would be strange. I think you maybe just didn't recognize it as being a > triggered update. > > > >- Does IGRP use a database like RIP ? or not ? > > It probably uses something like a database. For some reason, there aren't > very good show commands for igrp though. Of course there's show ip route > and show ip route igrp, but I don't know of others..... > > By the way, when trying to figure out IGRP, I go to this old paper here: > > http://www.cisco.com/warp/public/103/5.html > > Hope that helps. > > Priscilla > > >Can I see the database like > >"show ip rip database" ? > > > > > >thanks a lot. > > > > > >Stephane > ________________________ > > Priscilla Oppenheimer > http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=41975&t=41763 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
