Routing Question - Duplicate Route???

p-allen · ‎04-02-2007

Would this routing table cause any issues? Mainly concerned with the 192.168.1.0/24 and 192.168.1.8/30

show ip route 192.168.1.0

Routing entry for 192.168.1.0/24, 5 known subnets

Variably subnetted with 3 masks

Redistributing via eigrp 1

D 192.168.1.8/30 [90/63232] via 192.234.179.151, 07:07:16, Vlan100

D EX 192.168.1.10/32 [170/63232] via 192.234.179.151, 07:07:16, Vlan100

D 192.168.1.12/30 [90/63232] via 192.234.179.170, 07:07:17, Vlan100

D EX 192.168.1.14/32 [170/63232] via 192.234.179.170, 07:07:17, Vlan100

D 192.168.1.0/24 [90/65792] via 192.234.179.125, 00:37:19, Vlan100

Danilo Dy · ‎04-02-2007

The more specific route (longer prefix /30) will take priority over less specific route (shorter prefix /24). Therefore, 192.168.1.8/30 will be routed to 192.234.179.151. All other host under 192.168.1.0/24 (except 192.168.1.8/30 and 192.168.1.12/30) will be routed to 192.234.179.125

Richard Burts · ‎04-02-2007

Phil

I do not see anything here that would cause issues. I see that EIGRP has learned 5 entries about the addres space: it has learned a /24 from one neighbor (192.234.179.125), it has learned a more specific /30 and /32 from another neighbor (192.234.179.151), and it has learned another more specific /30 and /32 from a third neighbor (192.234.179.170).

I am not sure what it means but I note that the /32 address is included within the /30 subnet and is advertised as EIGRP external so the /32 came via redistribution of something whle the /30 came via a network statement.

It is not a problem to have multiple entries which in a sense overlap each other or are contained within each other. The /32 is within the /30 which is within the /24. The way that IOS does route lookup is on the basis of longest match. So even though different neighbors are advertising different parts of the address space we should route to the correct neighbor.

HTH

Rick

HTH

Rick

Jon Marshall · ‎04-02-2007

Phil

Rick has covered this in great detail. The only thing i would like to add is that if your link to 192.234.179.151 goes down then the next best route will be chosen, in this case 192.168.1.0/24 via 192.234.179.125. This may or may not be what you want depending on the topology of your network, speed of links etc.

HTH

Jon