Cisco Ccnp / Bsci Certification: Route Redistribution And The Seed Metric

In the first part of that free CCNP / BSCI tutorial, we looked at how leaving one simple word out of our route redistribution configuration - "subnets" - resulted in an incomplete routing table when redistribtuing routes from RIP to OSPF. (If you missed that part of the tutorial, visit my website's "Free Tutorials" section.) Today, we'll look at redistributing OSPF routes into RIP and identify a second common redistribution error. We are using a three-router network.
R5 is running RIP, R1 is serving as a hub between R5 and R3 and is running RIP and OSPF, and R3 is running OSPF. To begin that lab, we'll add three loopbacks to R3 and advertise them to R1 via OSPF. R3(config)#int loopback33 R3(config-if)#ip address 33.3.3.3 255.255.255.255 R3(config-if)#int loopback34 R3(config-if)#ip address 34.3.3.3 255.255.255.255 R3(config-if)#int loopback35 R3(config-if)#ip address 35.3.3.3 255.255.255.255 R3(config-if)#router ospf 1 R3(config-router)#network 33.3.3.3 0.0.0.0 area 1 R3(config-router)#network 34.3.3.3 0.0.0.0 area 1 R3(config-router)#network 35.3.3.3 0.0.0.0 area 1 R1 sees all three of these routes in its routing table. R1#show ip route ospf 34.0.0.0/32 is subnetted, 1 subnets O IA 34.3.3.3 [110/65] via 172.12.123.3, 00:00:55, Serial0 35.0.0.0/32 is subnetted, 1 subnets O IA 35.3.3.3 [110/65] via 172.12.123.3, 00:00:45, Serial0 33.0.0.0/32 is subnetted, 1 subnets O IA 33.3.3.3 [110/65] via 172.12.123.3, 00:00:55, Serial0 We'll at that moment redistribute these routes into RIP on R1. Remember the "subnets" option we talked about in the first part of this tutorial?

There is no such option when redistributing OSPF routes into RIP, as IOS Help shows us. R1(config)#router rip R1(config-router)#redistribute ospf 1 ?

match Redistribution of OSPF routes metric Metric for redistributed routes route-map Route map reference vrf VPN Routing/Forwarding Instance R1(config-router)#redistribute ospf 1 The routes have been redistributed into RIP with the redistribute ospf 1 command.
(The "1" is the OSPF process number.) Let's look at R5 and see the results. R5#show ip rotue rip R5# The routes aren't there, but we didn't get a warning from the router that we needed to do anything else.

What is the trouble? The trouble is that RIP requires a seed metric to be specified when redistributing ruotes into that protocol.
A seed metric is a "starter metric" that gives the RIP process a metric it can work with. The OSPF metric of cost is incomprehensible to RIP, since RIP's sole mertic is hop count. We've got to give RIP a metric it understands when redistributing rotues into that protocol, so let's go back to R1 and do so. R1(config)#router rip R1(config-router)#no redistribute ospf 1 R1(config-router)#redistribute ospf 1 metric 2 R5 at that moment sees the routes.
Note that the metric contained in the brackets is the seed metric. R5#show ip route rip 34.0.0.0/32 is subnetted, 1 subnets R 34.3.3.3 [120/2] via 100.1.1.1, 00:00:24, Ethernet0 35.0.0.0/32 is subnetted, 1 subnets R 35.3.3.3 [120/2] via 100.1.1.1, 00:00:24, Ethernet0 33.0.0.0/32 is subnetted, 1 subnets R 33.3.3.3 [120/2] via 100.1.1.1, 00:00:24, Ethernet0 If you read the previous tutorial, you may have noticed that we did not specify a seed metric for OSPF. OSPF does not require a seed metric to be set during redistribution. You also noticed that the router did tell us that there might be a trouble when we left the "subnets" otpion out of RIP>OSPF redistribution, but the router didn't tell us anything about a seed metric when we performed OSPF>RIP redistribution. This is a detial you must know by heart in order to make your route redistribution successful!