Route Redistribution Seed Metrics

[beerilavi]

Hi,

Just a quick question regarding seed metrics with route redistribution; why is that the IOS will allow you to redistribute without actually specifying a seed metric? For some protocols this implies an infinite metric and the route is considered unreachable, and therefore not advertised to neighboring routers, thus defeating the purpose of redistribution.

Is this a glitch in the command syntax, has it been updated, anybody know why this is so?

Thanks,

Beeri

[Deepak Kumar]

Hi,

It's not a glitch in command. It is giving flexibility to an admin to avoid some long syntax if there are multiple retributions. You can use the same metric as a default for all redistribution (Using the default-metric command). It will save your work because it eliminates the need for defining the metric separately for each redistribution.

Regards,

Deepak Kumar

[beerilavi]

Hi Deepak,

I understand it provides for granularity, however, both RIP and EIGRP have an infinite seed metric by default. Granted, other protocols such as IS-IS and BGP behave differently, so I can only think that this syntax exists to serve redistribution with these other routing protocols.

Basically, if you accept the default syntax and are redistributing with RIP or EIGRP, you are achieving absolutely nothing.

Thanks,

Beeri

[Richard Burts]

You are quite right that the seed metric is required in some circumstances and not required in other circumstances. That is why seed metric is not a required parameter in the redistribute command.

You are also quite right that you could configure redistribution in RIP or EIGRP without configuring a seed metric and not achieve the desired outcome. There are numerous instances in IOS where failure to specify appropriate parameters will mean that you do not achieve the result that you desire.

HTH

Rick

[beerilavi]

Hi Rick,

Personally, I was always taught to utilise the seed metric syntax to influence routing decisions in the case of redistribution. Short of running it and turning debug on, to your knowledge, if I configured redistribution in RIP or EIGRP without configuring a seed metric, would anything be redistributed, even between the redistributor and redistribute (routers), or would anything be modified from a routing perspective?

Thanks again,

Beeri

[Richard Burts · Accepted solution]

Beeri

The answer to your question of whether anything would be redistributed if you configure redistribution for RIP or EIGRP without configuring a seed metric depends on what you are redistributing. If you are redistributing from another dynamic protocol then nothing gets redistributed because your receiving protocol has no way of understanding the associated metric from the sending protocol. But if you were redistributing connected I believe that the connected subnets would be redistributed because your receiving protocol can understand the associated metric.

I agree with you that it is better to just always specify a seed metric when you configure redistribution.

HTH

Rick

[beerilavi]

Hi Rick,

From memory, connected and static routes fall under the category of not requiring a seed metric, though best practice would be to have a seed metric, especially if you have route maps and other factors you would like to influence the routing behaviour.

It's good to have an answer to question, I thank you for your generous time and feedback.

Thank you,

Beeri

[Richard Burts]

Beeri

You are quite welcome. I am glad that my explanations have been helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions that have helpful information. This has been an interesting discussion and I believe that some other participants will benefit from it. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

HTH

Rick