Default Route

typesh

Hey everyone,

I have a question on default-routes.

I have 3 routers connected: R1---99.0.0.0/24---R2----150.0.0.0/24----R3
R2's Serial 1 is 150.1.1.1
R3'2 Serial 1 is 150.1.1.2

I have enabled RIP on all 3 routers and all routers can ping each other.

On R2 i have set ip route 0.0.0.0 0.0.0.0 150.1.1.2 (which is R3).

I have set default-information originate on R2.

As I had hoped R* 0.0.0.0/0 [120/1] via 99.1.1.2, 00:00:22, Serial0 showed up in R1's routing table.

I went back to R2 and did no default-information originate

However the default route will not get out of R1's table. On R1 I did clear ip route * and debug ip rip

It appears that R2 is still sending the default route information as per the debug output:
R1#
*Mar 1 00:41:56.003: RIP: sending request on Serial0 to 224.0.0.9
*Mar 1 00:41:56.047: RIP: sending request on Serial0 to 224.0.0.9
*Mar 1 00:41:56.055: RIP: received v2 update from 99.1.1.2 on Serial0
*Mar 1 00:41:56.059: 0.0.0.0/0 via 0.0.0.0 in 1 hops
*Mar 1 00:41:56.103: 10.0.0.0/8 via 0.0.0.0 in 2 hops
*Mar 1 00:41:56.107: 150.1.0.0/16 via 0.0.0.0 in 1 hops
*Mar 1 00:41:56.119: RIP: received v2 update from 99.1.1.2 on Serial0
*Mar 1 00:41:56.123: 0.0.0.0/0 via 0.0.0.0 in 1 hops
*Mar 1 00:41:56.123: 10.0.0.0/8 via 0.0.0.0 in 2 hops
*Mar 1 00:41:56.127: 150.1.0.0/16 via 0.0.0.0 in 1 hops


Why would this be happening?


What is even more interesting is that R2 points to R3's Serial as its default route.
After I created the default route on R2 and issued default-information originate, R3 actually had the default route show up in its routing table (pointing back to R2s Serial - 150.1.1.1). R3 pointed back to R2 as its gateway of last resort and R2 pointed to R3 (150.1.1.2). This eventually went away.

Thanks



Edit:


Okay eventually the default-route learned through RIP got out of R1s routing table. But it took a lot longer than 30 seconds.

So on R2 I removed the default-route and created another. The new one was not connected to R1 or R3.

I again did default-information originate on R2.

As I had hoped, R1 and R3 learned of this default route. When I did no default-information originate on R2, it took I would say almost 10 minutes for it to disappear from R1 and R3's routing table. Also, even though I stopped the default-information originate on R2, when I did a debug ip rip on R1 and R3, I could still see this information being advertised.

Does default-information originate and no default-information originate have some type of delayed effect?

mikem2te

typesh wrote: »

On R2 i have set ip route 0.0.0.0 0.0.0.0 150.1.1.2 (which is R3).

Routing loop!! Not sure why you'd put a default route with the destination being another router which is part of the rip system. I thought you would put a default route and default information originate on the router on the edge of the RIP system eg to some eternal network such as an ISP network


Anyway, are you on a sim or real hardware, I quickly put your second scenario into GNS and the effect of adding / removing default information originate was immediate on the other routers, not 10 minutes

typesh

Hey thanks for your reply!

mikem2te wrote: »

Not sure why you'd put a default route with the destination being another router which is part of the rip system. I thought you would put a default route and default information originate on the router on the edge of the RIP system eg to some eternal network such as an ISP network

Not sure why I did this either. Was trying it out I guess... In my second trial I did put it on the edge.

mikem2te wrote: »

Anyway, are you on a sim or real hardware

Real hardware. (3) 2501s

I just did it again to make sure...

Same topology as above, except I created Loopback1 on R2 with 1.1.1.1/24 and set ip route 0.0.0.0 0.0.0.0 1.1.1.2 on R2
Routing table on R2:

Gateway of last resort is 1.1.1.2 to network 0.0.0.0

1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback1
C 99.0.0.0/8 is directly connected, Serial0
C 150.1.0.0/16 is directly connected, Serial1
S* 0.0.0.0/0 [1/0] via 1.1.1.2


RIP is enabled and working.

Issued default-information originate on R2. Verified it is in the running config:
router rip
version 2
network 99.0.0.0
network 150.1.0.0
default-information originate
no auto-summary


Checked routing table of R1 and R3. Default Route does not appear. It has now been 5 minutes and it has not appeared in the Routing Table of R1 and R3.

typesh

Okay... I tried yet again.

Cleared configs are trying again.

Same topology R1---99.0.0.0---R2---150.0.0.0---R3



This time I enabled RIPv2 on R1 and R2 only .

Created a default route on R2 by doing this:
ip route 0.0.0.0 0.0.0.0 150.1.1.2 (this address is an interface of R3).
issued router rip
issued default-information originate

Checked the routing table on R1 and there is no default route (I have waited about 10 mins again).

I went back to R2 and did clear ip route *
As soon as I did this, I went back to R1 and saw the default route was in R1's routing table.

So in this lab, the default-route does not immediately show up. It does not show up after 10 minutes. But it did show up after I cleared the ip routing table on R2.

I cannot understand what is happening here.

I'm going to try yet again...

Edit:

So I tried again...same thing.

I notice that when I do a clear ip route * on R2, then R1 learns of the default route. If I do not do a clear ip route * on R2, then R1 does not seem to learn of the route (at least not after 4 minutes as in this trial).


Edit

On R2 (which is the router that should be advertising the default route), I see this in the RIP Debug:
*Mar 1 00:12:32.843: RIP: sending v2 update to 224.0.0.9 via Serial0 (99.1.1.2)
*Mar 1 00:12:32.847: RIP: build update entries - suppressing null update

Does "suppressing null update" have anything to do with this problem?