offset list vs distribute-list, which one will be applied first

[ahmed_elemamn]

i'm asking about the order of operation when excuting both under eigrp

[Peter Paluch]

Hi Ahmed,

I am probably answering with a counterquestion but I would like to ask you why you believe that the order of these two mechanisms is important.

To be honest, I do not know in what order are these two evaluated internally in the EIGRP code. However, I do not believe this makes any difference because the distribute-list and offset-list perform independent actions, and cannot override each other:

• A distribute-list permits or denies a particular prefix to be advertised out or accepted in. It does not touch its metric.
• An offset-list increases the metric of a particular prefix by a specified amount. It does not prevent the prefix from being advertised out or accepted in.

So, in either order (you first modify the metric and then permit/deny the prefix, or you first permit/deny the prefix and then modify its metric if it was permitted), the result is the same. From the efficiency perspective, it would makemore  sense to apply the distribute-list first, and evaluate the offset-list later (no reason to tweak the metrics of routes that will be denied either way), but this is purely a matter of internal implementation.

Feel welcome to ask further!

Best regards,
Peter

[Georg Pauwen]

Hello,

in addition to Peter's remarks, out of curiosity I set up a small lab with both a distribute and an offset list for a specific prefix. Since the distribute list keeps the prefix from making it into the EIGRP topology table, the offset list is never applied. In that regard, the distribute list is takes 'precedence'...