Adding a new MPLS link to our HQ

[carl_townshend]

Hi all

We are going to install another MPLS link to our provider, so we should learn all the routes from the mpls on this new router.

My question is, how do we select what router will be used as primary? the current router is a 10meg circuit, the new is 20 meg, will BGP automatically sort this out or will be need to influence it ?

Whats the best way to migrate this ?

[rsimoni]

Hi Carl,

you need to influence which exist point must be taken as BGP does not take into consideration link bandwidth.

You have multiple way to do so depending the topology you have. If you have a second link towards the same SP on the same router you might use Local Preference or Weight to influence the exit traffic (from the HQ point of view). For the ingress traffic you need to influence your SP routing but you need to check if their routing can be influenced by you. Easisest way is to configure MED or as-path prepend, or simply ask your provider to influence the routing as per your indication (they might configure LP on their devices for instance).

If you have 2 routers on your HQ, if they are on the same LAN a FHRP protocol such HRSP or VRRP might be what you need. Again this works for the egress traffic only, for the ingress one either you use MED or as-path prepend or you work with your SP.

If you are connected to 2 different SP as-path prepend is the only way. You first need to know what is the possible max as-path lenght which might be added by each SP and then configure the correct number of as-path prepend iteration (the number of time the same as-path is appended to your prefix).

Riccardo

[icewulfie]

I would highly recommend you look into performance routing as you can load balance both links. BGP is incapable of this to a degree.