Certification Tests
Cisco CCNP / BSCI Certification: Route Redistribution And The Seed Metric
In the first part of this 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 redistributing 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 another 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 this 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 now 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 route 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 problem?
The problem is that RIP requires a seed metric to be specified when redistributing routes 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 metric is hop count. We've got to give RIP a metric it understands when redistributing routes 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 now 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 problem when we left the "subnets" option 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 detail you must know by heart in order to make your route redistribution successful!
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage, home of free CCNP and CCNA tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages. For a FREE copy of his latest e-books, ?How To Pass The CCNA? and ?How To Pass The CCNP?, just visit the website! You can also get FREE CCNA and CCNP exam questions every day! Pass the CCNP exam with The Bryant Advantage!
Chris Bryant
Similar articles
Cisco CCNP / BSCI Exam Tutorial: 10 ISIS Details You Must Know!
Earning your CCNP certification and passing the BSCI exam depends on knowing the details of many Cisco technologies, ISIS chief among them. To help you prepare for exam success, here's a list of ISIS terminology and basic concepts that will help you pass this tough exam. Read more →Cisco CCNP / BCMSN Exam Tutorial: The Core Layer Of Cisco's Three-Layer Model
In this section, you're going to be reintroduced to a networking model you first saw in your CCNA studies. No, it's not the OSI model or the TCP/IP model - it's the Cisco Three-Layer Hierarchical Model. Read more →Cisco CCNP / BSCI Exam Tutorial: OSPF Route Redistribution Review
OSPF route redistribution is an important topic on the BSCI exam, and it's a topic full of details and defaults that you need to know for the exam room and the job. Read more →Cisco CCNP / BSCI Exam Tutorial: Route Summarization
Preparing to pass the BSCI exam and earn your Cisco CCNP? Route summarization is just one of the many skills you'll have to master in order to earn your CCNP. Read more →Aphorism
Technology is dominated by two types of people: those who understand what they do not manage, and those who manage what they do not understand.