Cisco CCNA CCNP Certification OSPF E2 vs. E1 Routes

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Cisco CCNA/CCNP Certification: Understanding OSPF E2 vs. E1 Routes

Summary

Mastering OSPF details is crucial for success in the CCNA and CCNP exams. This tutorial by Chris Bryant, CCIE

12933, explains the differences between two essential OSPF route types: E2 and E1.

Article Body

OSPF is a key topic in both the CCNA and CCNP exams, requiring an eye for detail. Unlike simpler protocols like RIP and IGRP, OSPF offers multiple route types. Here’s a look at two of them: E1 and E2.

Understanding OSPF Route Types

In Cisco routing tables, you’ll encounter various OSPF 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 & N2: OSPF NSSA External Type 1 & 2
- E1 & E2: OSPF External Type 1 & 2
- E: EGP

Let's focus on E1 and E2.

Route Redistribution and ASBRs

Route redistribution involves sharing routes from one protocol into another domain. For this, a router running OSPF that incorporates routes from another protocol becomes an Autonomous System Border Router (ASBR).

Example: Router R1 runs both OSPF and RIP, while R4 is in the OSPF domain. To enable R4 to learn RIP routes from R1, route redistribution is necessary, typically appearing as E2 routes on R4.

```plaintext
R4

show ip route ospf

O E2 5.1.1.1 [110/20] via 172.34.34.3, 00:33:21, Ethernet0
...
```

Understanding E2 Routes

E2 routes are the default for redistributed routes and reflect only the cost from the ASBR to the destination. The path cost from R4 to R1 is not included.

Switching to E1 Routes

For the entire path cost to be displayed, routes must be redistributed as E1:

```plaintext
R1

conf t

R1(config)

router ospf 1

R1(config-router)

redistribute rip subnets metric-type 1

```

Now, on R4, the routes appear as E1, reflecting the full path cost:

```plaintext
O E1 5.1.1.1 [110/94] via 172.34.34.3, 00:33:21, Ethernet0
...
```

Conclusion

Understanding the distinction between E1 and E2 routes is crucial for CCNP exam success and managing a production router’s routing table. Good luck with your studies!

You can find the original non-AI version of this article here: Cisco CCNA CCNP Certification OSPF E2 vs. E1 Routes.

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