Routes learnt by routing protocols with same AD/metric

From: William Chen (kwchen@netvigator.com)
Date: Wed Dec 17 2003 - 04:18:28 GMT-3

Dear all,

   I think it should be a simple question, but I just never think about it.

   If a route is learn from different routing protocol with same AD, and same
metric. What is the preference order? Is there any doc talking about that?

   Look at the following example of a router running EIGRP AS30/EIGRP AS40 and learn same routes. Can I make the router to load balancing the routes?

CAT1#sh ip eigrp top
IP-EIGRP Topology Table for AS(30)/ID(223.1.1.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 172.16.200.0/22, 1 successors, FD is 281856
         via Summary (281856/0), Null0
P 172.16.201.0/24, 1 successors, FD is 281856
         via 172.16.30.20 (281856/25856), Vlan30
P 172.16.202.0/24, 1 successors, FD is 281856
         via 172.16.30.20 (281856/25856), Vlan30
P 172.16.203.0/24, 1 successors, FD is 281856
         via 172.16.30.20 (281856/25856), Vlan30
P 172.16.30.0/24, 1 successors, FD is 281600
         via Connected, Vlan30
P 172.16.120.0/24, 1 successors, FD is 281856
         via 172.16.30.20 (281856/25856), Vlan30
P 172.16.110.0/24, 1 successors, FD is 25856
         via Rconnected (25856/0)
IP-EIGRP Topology Table for AS(40)/ID(223.1.1.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 172.16.201.0/24, 0 successors, FD is Inaccessible
         via 172.16.40.20 (281856/25856), Vlan40
P 172.16.202.0/24, 0 successors, FD is Inaccessible
         via 172.16.40.20 (281856/25856), Vlan40
P 172.16.203.0/24, 0 successors, FD is Inaccessible
         via 172.16.40.20 (281856/25856), Vlan40
P 172.16.40.0/24, 1 successors, FD is 281600
         via Connected, Vlan40
P 172.16.120.0/24, 0 successors, FD is Inaccessible
         via 172.16.40.20 (281856/25856), Vlan40
P 172.16.110.0/24, 1 successors, FD is 25856
         via Rconnected (25856/0)

CAT1#r
Codes: C - connected, S - static, I - IGRP, 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, E - EGP
       i - IS-IS, 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

Gateway of last resort is not set

     1.0.0.0/24 is subnetted, 1 subnets
C 1.1.1.0 is directly connected, Loopback84
C 223.1.1.0/24 is directly connected, Loopback83
     172.16.0.0/16 is variably subnetted, 8 subnets, 2 masks
D 172.16.200.0/22 is a summary, 00:07:22, Null0
D EX 172.16.201.0/24 [170/281856] via 172.16.30.20, 00:07:22, Vlan30
D EX 172.16.202.0/24 [170/281856] via 172.16.30.20, 00:07:22, Vlan30
D EX 172.16.203.0/24 [170/281856] via 172.16.30.20, 00:07:22, Vlan30
C 172.16.40.0/24 is directly connected, Vlan40
C 172.16.30.0/24 is directly connected, Vlan30
D EX 172.16.120.0/24 [170/281856] via 172.16.30.20, 00:07:23, Vlan30
C 172.16.110.0/24 is directly connected, Loopback110
     129.1.0.0/24 is subnetted, 1 subnets
C 129.1.1.0 is directly connected, Loopback82
     126.0.0.0/24 is subnetted, 1 subnets
C 126.1.1.0 is directly connected, Loopback81

Best Regards,
William Chen

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