Explain the Routing table behaviour

Routing & Switching
1

Hi i am new and preparing the CCNA exam, I just ceated one topology and running the Rip version 2 and Eigrp , When i look the routing table R0 and R3 i seen the Rip learned the 4 routes and Eigrp learned 3 Routes

Document1

2

Hello Mohammad

Notice that in both cases RIP states that 40.0.0.0/8 “is possibly down, routing via…” This means that this route’s holddown timer has been expired and essentially has been removed from the routing table. After 3 minutes of no updates (holddown timer), routes are marked in RIP database as “possibly down” and after an additional 60 seconds, of no updates, routes are flushed from RIP database.
RIP seems to have stopped advertising this network and thus it has been removed. See if a RIP router connected to the 40.40.40.40 network (such as Router 2) is not correctly advertising RIP information.

So, the RIP routes to 40.0.0.0 in the routing table are not active, not functioning, so it’s like they’re not in the routing table at all.

I hope this has been helpful!

Laz

3

ok. But when i configured “no auto summary” on all the router under Rip . I am only able to see the EIGRP routes . What happen to RIp ?

4

Hi Mohammad,

In your screenshot, you have two entries:

* RIP: 40.0.0.0/8
* EIGRP: 40.40.40.0/24

With auto-summary enabled, RIP advertises the classful network so that’s 40.0.0.0/8. Once you disable auto-summary, it will advertise the actual subnet (40.40.40.0/24).

Your router now has two sources for the exact same router, one from RIP, one from EIGRP. Which one does it install it in the routing table? You can’t install both so it has a decision to make.

This decision is based on the administrative distance:

EIGRP has a lower (better) administrative distance than RIP so that’s why the EIGRP route is installed and the RIP route ignored.

Hope this helps!

Rene

1 Like
5

Thanks. If I change the rip AD to 90 then both rip and eigrp will do load ballance?

6

I’m afraid not. Load balancing will only work for one “source”:

- If you learn two paths through RIP with the same metric.
- If you learn two paths through EIGRP with the same metric. (EIGRP also supports unequal cost load balancing).
- If you use two static routes with different next hops.

Even if you set the AD the same for RIP/EIGRP, OSPF/EIGRP, RIP/OSPF, or anything else then IOS still has a “preference” for one routing protocol over the other.

Rene

1 Like
7

Thanks Rene Molenaar .