Any show command to show the EIGRP feasible succcessor

[Difan Zhao]

Hi gents,

How do I know if a path in my "show ip eigrp topology" table is FS or not?

EIGRP-IPv4 Topology Entry for AS(100)/ID(10.128.121.1) for 10.128.0.0/14
 State is Passive, Query origin flag is 1, 1 Successor(s), FD is 24096000
 Descriptor Blocks:
 10.132.31.254 (Tunnel11), from 10.132.31.254, Send flag is 0x0
 Composite metric is (24096000/22816000), route is Internal
 Vector metric:
 Minimum bandwidth is 128 Kbit
 Total delay is 160000 microseconds
 Reliability is 1/255
 Load is 1/255
 Minimum MTU is 1
 Hop count is 1
 Originating router is 10.135.128.151
 10.132.63.254 (Tunnel12), from 10.132.63.254, Send flag is 0x0
 Composite metric is (2564352000/2563072000), route is Internal
 Vector metric:
 Minimum bandwidth is 1 Kbit
 Total delay is 170000 microseconds
 Reliability is 1/255
 Load is 1/255
 Minimum MTU is 1
 Hop count is 1
 Originating router is 10.135.128.152

So based on my understanding, the second path is not the FS. However how do I know that for sure? There is no flag to identify this being a FS or not.

Thanks,

Difan

[cofee]

10.132.31.254 (Tunnel11), from 10.132.31.254, Send flag is 0x0
Composite metric is (24096000/22816000), route is Internal

10.132.63.254 (Tunnel12), from 10.132.63.254, Send flag is 0x0
Composite metric is (2564352000/2563072000), route is Internal

- 10.132.63.254 is neither a successor nor a feasible successor because its reported distance 2563072000to destination network is more than composite metric 24096000 . Reported distance has to be less than successor's composite metric to be eligible to become a feasible successor.

Below is output from show ip eigrp topology :

very last entry has a feasible successor, now it doesn't say that it's a feasible successor but just by looking at it you know there are two routes for that destination and it clearly states that it has 1 successor even though there are two entries and by looking at the reported distance of 10.0.34.4 (4352/1792) you can tell it's a feasible successor because its RD is lower than composite metric of successor. You also have the option of tweaking FS metric to install in the RIB for unequal load balancing. But in my opinion biggest advantage for having a back up route is faster convergence of eigrp as it won't have to send out query for the lost route.

If you want to see all eigrp links then use " show ip eigrp topology all-links"

R3# show ip eigrp topology

IP-EIGRP Topology Table for AS(1)/ID(3.3.3.3)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 10.0.12.0/24, 2 successors, FD is 3840
        via 10.0.13.1 (3840/1280), Serial1/0
        via 10.0.23.2 (3840/1280), Serial1/1
P 10.0.13.0/24, 1 successors, FD is 2560
        via Connected, Serial1/0
P 10.0.23.0/24, 1 successors, FD is 2560
        via Connected, Serial1/1
P 10.0.45.0/24, 2 successors, FD is 3840
        via 10.0.34.4 (3840/1280), Serial1/2
        via 10.0.35.5 (3840/1280), Serial1/3
P 10.0.34.0/24, 1 successors, FD is 2560
        via Connected, Serial1/2
P 10.0.35.0/24, 1 successors, FD is 2560
        via Connected, Serial1/3
P 192.168.5.0/24, 1 successors, FD is 3072
        via 10.0.35.5 (3072/512), Serial1/3
        via 10.0.34.4 (4352/1792), Serial1/2

I hope you will find this useful.

[Difan Zhao]

So there is no flag or indicator in the show topology output to say whether this is a FS or not. You always have to calculate yourself by comparing the two values?

Thanks

[cofee]

Well if you look at the last entry from my previous post that has a feasible successor eigrp tells you that there is 1 successor even it has dual entry so the second route is a feasible successor and you can also look at the RIB because it will only show you primary route.

[cofee]

But yes you are right and to my knowledge there is no flag or eigrp won't say in clear words that secondary path in the topology table is a feasible successor.

[Difan Zhao]

I see. So without the "all-link"option, it only shows the sucessor and FS. So with the "all-link" option if the prefix has both paths, and only shows one without the option, then the other one must not be the FS, correct?

[cofee · Accepted solution]

* With all-link option it will show you "successor, feasible successor and non-successor routes".

* Without all-link option it will only show " successor and feasible successor routes" if it's only showing 1 route then that must be a Successor, if showing two routes then they are either both successors doing equal load balancing or 1 is a successor and the other one is a FS.

You can also compare the global RIB and eigrp topology table for more details.

[Difan Zhao]

Thank you 

[cofee]

Your welcome!