bgp inbound routing

[jay_7301]

Hello,

I was wondering we have 2 border routers to 2 different tier 1 providers and seem to use MED for inbound path selection. I was wondering how this works as BGP AS path is well above this so will MED even get looked at? unless there is a tie in the AS path?

also i see that med isn't the best inbound method to use prepend is better. however we do use bgp always-compare-med will this make a difference on inbound selection with uplinks to different isp?

Thanks

[Traian Bratescu]

Hi,

MED is an optional nontransitive attribute - this means that you would have to peer to the same provider in order to try to influence inbound policy with this attribute.

Usually, the inbound policy is influenced using as-prepend as you stated and outbound decision using local preference.

You should also take a look at the provider policy; they might already implement routing preferences based on communities.

Traian

[jay_7301]

do you get any advantages of doing this at peering exchanges? i can see we have set a MED inbound here on some of them?

[Traian Bratescu]

perhaps you are actually influencing the outbound policy using MED?