RIP Route propagation issue

rasmus.elmholt · ‎11-24-2016

Hi

I have a question about RIP route propagation.

I have always thought that RIP sends all the networks it receives from its neighbors and transmit those networks to all other neighbors, except for the split-horison rule.

But in a test I found that it only forwards the networks it receives if they are installed in the routing table.

I have this setup(see attachement):

R1 <----------> R2 <-----------> R3 <-----------> R4

R3#debug ip rip
RIP protocol debugging is on
R3#
*Nov 24 11:59:31.454: RIP: sending v2 update to 224.0.0.9 via Ethernet0/0 (192.168.20.3)
*Nov 24 11:59:31.454: RIP: build update entries
*Nov 24 11:59:31.454: 192.168.30.0/24 via 0.0.0.0, metric 1, tag 0
*Nov 24 11:59:32.121: RIP: sending v2 update to 224.0.0.9 via Ethernet0/1 (192.168.30.3)
*Nov 24 11:59:32.121: RIP: build update entries
*Nov 24 11:59:32.121: 0.0.0.0/0 via 0.0.0.0, metric 2, tag 0
*Nov 24 11:59:32.121: 10.0.0.1/32 via 0.0.0.0, metric 2, tag 0
*Nov 24 11:59:32.121: 10.0.0.2/32 via 0.0.0.0, metric 2, tag 0
*Nov 24 11:59:32.121: 192.168.20.0/24 via 0.0.0.0, metric 1, tag 0
R3#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config)#ip route
*Nov 24 11:59:45.621: RIP: received v2 update from 192.168.20.2 on Ethernet0/0
*Nov 24 11:59:45.621: 0.0.0.0/0 via 0.0.0.0 in 1 hops
*Nov 24 11:59:45.621: 10.0.0.1/32 via 0.0.0.0 in 1 hops
*Nov 24 11:59:45.621: 10.0.0.2/32 via 0.0.0.0 in 1 hops
R3(config)#ip route 0.0.0.0 0.0.0.0 192.168.20.
*Nov 24 11:59:57.225: RIP: sending v2 update to 224.0.0.9 via Ethernet0/0 (192.168.20.3)
*Nov 24 11:59:57.225: RIP: build update entries
*Nov 24 11:59:57.225: 192.168.30.0/24 via 0.0.0.0, metric 1, tag 0
R3(config)#ip route 0.0.0.0 0.0.0.0 192.168.20.2
R3(config)#end
R3#show i
*Nov 24 12:00:01.613: RIP: sending v2 update to 224.0.0.9 via Ethernet0/1 (192.168.30.3)
*Nov 24 12:00:01.613: RIP: build update entries
*Nov 24 12:00:01.613: 0.0.0.0/0 via 0.0.0.0, metric 16, tag 0
*Nov 24 12:00:01.613: 10.0.0.1/32 via 0.0.0.0, metric 2, tag 0
*Nov 24 12:00:01.613: 10.0.0.2/32 via 0.0.0.0, metric 2, tag 0
*Nov 24 12:00:01.613: 192.168.20.0/24 via 0.0.0.0, metric 1, tag 0
*Nov 24 12:00:02.581: %SYS-5-CONFIG_I: Configured from console by console
R3#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
 D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
 N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
 E1 - OSPF external type 1, E2 - OSPF external type 2
 i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
 ia - IS-IS inter area, * - candidate default, U - per-user static route
 o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
 a - application route
 + - replicated route, % - next hop override

Gateway of last resort is 192.168.20.2 to network 0.0.0.0

S* 0.0.0.0/0 [1/0] via 192.168.20.2
 10.0.0.0/32 is subnetted, 2 subnets
R 10.0.0.1 [120/1] via 192.168.20.2, 00:00:18, Ethernet0/0
R 10.0.0.2 [120/1] via 192.168.20.2, 00:00:18, Ethernet0/0
 192.168.20.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.20.0/24 is directly connected, Ethernet0/0
L 192.168.20.3/32 is directly connected, Ethernet0/0
 192.168.30.0/24 is variably subnetted, 2 subnets, 2 masks
C 192.168.30.0/24 is directly connected, Ethernet0/1
L 192.168.30.3/32 is directly connected, Ethernet0/1
R3#
*Nov 24 12:00:03.276: RIP: sending v2 flash update to 224.0.0.9 via Ethernet0/0 (192.168.20.3)
*Nov 24 12:00:03.276: RIP: build flash update entries
*Nov 24 12:00:03.276: 0.0.0.0/0 via 0.0.0.0, metric 16, tag 0
*Nov 24 12:00:03.276: RIP: sending v2 flash update to 224.0.0.9 via Ethernet0/1 (192.168.30.3)
*Nov 24 12:00:03.276: RIP: build flash update entries
*Nov 24 12:00:03.276: 0.0.0.0/0 via 0.0.0.0, metric 16, tag 0
*Nov 24 12:00:03.615: RIP: received v2 update from 192.168.30.4 on Ethernet0/1
*Nov 24 12:00:03.615: 0.0.0.0/0 via 0.0.0.0 in 16 hops (inaccessible)
R3#
*Nov 24 12:00:08.281: RIP: received v2 update from 192.168.30.4 on Ethernet0/1
*Nov 24 12:00:08.281: 0.0.0.0/0 via 0.0.0.0 in 16 hops (inaccessible)
R3#
*Nov 24 12:00:13.178: RIP: received v2 update from 192.168.20.2 on Ethernet0/0
*Nov 24 12:00:13.178: 0.0.0.0/0 via 0.0.0.0 in 1 hops
*Nov 24 12:00:13.178: 10.0.0.1/32 via 0.0.0.0 in 1 hops
*Nov 24 12:00:13.178: 10.0.0.2/32 via 0.0.0.0 in 1 hops
R3#
*Nov 24 12:00:24.138: RIP: sending v2 update to 224.0.0.9 via Ethernet0/0 (192.168.20.3)
*Nov 24 12:00:24.138: RIP: build update entries
*Nov 24 12:00:24.138: 0.0.0.0/0 via 0.0.0.0, metric 16, tag 0
*Nov 24 12:00:24.138: 192.168.30.0/24 via 0.0.0.0, metric 1, tag 0
R3#
*Nov 24 12:00:31.484: RIP: sending v2 update to 224.0.0.9 via Ethernet0/1 (192.168.30.3)
*Nov 24 12:00:31.484: RIP: build update entries
*Nov 24 12:00:31.484: 0.0.0.0/0 via 0.0.0.0, metric 16, tag 0
*Nov 24 12:00:31.484: 10.0.0.1/32 via 0.0.0.0, metric 2, tag 0
*Nov 24 12:00:31.484: 10.0.0.2/32 via 0.0.0.0, metric 2, tag 0
*Nov 24 12:00:31.484: 192.168.20.0/24 via 0.0.0.0, metric 1, tag 0
R3#
*Nov 24 12:00:37.095: RIP: received v2 update from 192.168.30.4 on Ethernet0/1
*Nov 24 12:00:37.095: 0.0.0.0/0 via 0.0.0.0 in 16 hops (inaccessible)
R3#
*Nov 24 12:00:39.907: RIP: received v2 update from 192.168.20.2 on Ethernet0/0
*Nov 24 12:00:39.907: 0.0.0.0/0 via 0.0.0.0 in 1 hops
*Nov 24 12:00:39.907: 10.0.0.1/32 via 0.0.0.0 in 1 hops
*Nov 24 12:00:39.907: 10.0.0.2/32 via 0.0.0.0 in 1 hops
R3#un all

Here I add a default static on R3 and then it sendt a infinite route downstream. Why is this happening? I cant find any documentaiton that says only RIP routes installed in the routing table is forwarded.


R3#show run | sec router rip
router rip
 version 2
 network 192.168.20.0
 network 192.168.30.0
 no auto-summary
R3#

Richard Burts · ‎11-24-2016

Perhaps it would help to think about how RIP processes to generate its outbound routing advertisement. RIP looks through the local routing table for the RIP learned routes and adds to that the locally generated route entries and that is what will be advertised. If the router receives a RIP advertisement from a neighbor and a prefix in that advertisement is not used because the router has that route with a more attractive administrative distance then it does not put that route into its routing table. And so that prefix will not be advertised to its peers because when RIP checks the routing table the prefix is not a RIP learned route.

HTH

Rick

HTH

Rick