Cisco CCNP BSCI Certification Route Redistribution And The Seed Metric
Below is a MRR and PLR article in category Computers Technology -> subcategory Computer Certification.
Cisco CCNP/BSCI Certification: Understanding Route Redistribution and the Seed Metric
Overview:
Route redistribution might seem straightforward, but the details can be crucial, especially during real-world application or while tackling the BSCI exam. This guide, illustrated by Chris Bryant, CCIE
12933, explores a key aspect of route redistribution.
Redistributing Routes: A Practical Scenario
In the initial part of this tutorial, we discussed how omitting the word "subnets" can lead to an incomplete routing table when redistributing from RIP to OSPF. Today, we'll focus on redistributing OSPF routes into RIP and tackle a common error.
Network Setup
Consider a network with three routers:
- R5 runs RIP.
- R1 acts as a hub between R5 and R3 and supports both RIP and OSPF.
- R3 operates OSPF.
We'll add three loopbacks to R3 and advertise them via OSPF to R1.
```plaintext
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-router)
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 should now have all these routes in its routing table.
```plaintext
R1
show ip route ospf
34.3.3.3 [110/65] via 172.12.123.3, Serial035.3.3.3 [110/65] via 172.12.123.3, Serial0
33.3.3.3 [110/65] via 172.12.123.3, Serial0
```
Redistributing OSPF into RIP
On R1, we aim to redistribute these routes into RIP. Unlike RIP to OSPF, there is no "subnets" option when redistributing OSPF to RIP.
```plaintext
R1(config)
router rip
R1(config-router)redistribute ospf 1
```However, the routes aren't appearing on R5. Why?
The Importance of the Seed Metric
RIP requires a seed metric to understand redistributed routes. OSPF's cost is not compatible with RIP, which uses hop count. Let's set a compatible metric for RIP.
```plaintext
R1(config)
router rip
R1(config-router)no redistribute ospf 1
R1(config-router)redistribute ospf 1 metric 2
```Now, R5 will display the routes correctly, and the metric in brackets indicates the seed metric.
```plaintext
R5
show ip route rip
34.3.3.3 [120/2] via 100.1.1.1, Ethernet035.3.3.3 [120/2] via 100.1.1.1, Ethernet0
33.3.3.3 [120/2] via 100.1.1.1, Ethernet0
```
In our previous tutorial, we didn't need a seed metric for OSPF. However, keep in mind that routers won't remind you about the seed metric when performing OSPF to RIP redistribution. Mastering this detail is essential for successful route redistribution!
You can find the original non-AI version of this article here: Cisco CCNP BSCI Certification Route Redistribution And The Seed Metric.
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