Local Preference- MPLS sites

[foysol_bgd]

Hi, 

I have three sites (SiteA, SiteB, SiteC) connected to same MPLS provider. The three sites all have same BGP AS number and with as override feature everything is working as expected. 

In Site A and Site B I have confifured Local Preference to prefer SiteA than Site B and advertise a static route from both the sites. 

As the three sites belong to same AS number (iBGP) I belive I should see the local preference value in the Site C for the routes advertised from Site A and Site B when I issue the "show ip bgp .." commnad. Am I right?

[Akash Agrawal]

Hi,

I dont think local preference attribute will be carried in bgp update end to end. LP attribute is local to AS and here you are exchanging routes via service provider AS which is eBGP session. Better use AS-path attribute to prefer particular site. You can do as-path prepend at site-B while advertising routes to service provider.

-Akash

[foysol_bgd]

Hi, 

What is the best way to influence the core routing in MPLS when client will use Local preference to influence the outbound path from a particular site.  

http://www.gossamer-threads.com/lists/cisco/nsp/96139

Is there any way to influence without modifying the PE config that is mentioned in the above post?

I am trying to achieve something so when client will influence outbound path from a particular site the core will be transparent and I dont need to make any changes in PE router. 

[loris.marcellini]

Hello foysol_bgd,

let's make a step backward, we are basically talking about BGP traffic politics, there are different ways to influence traffic inbound and outbound:

Inbound:

• Local preference
• Weight
  
  

Outbound:

• AS Path-prepend
• MED

There are no exact methods to avoid traffic to take whatever path in Inbound direction, we can try by using BGP features and PA but, nobody will never know what will happen out there in the Internet.
My personal advice is the selective advertisement, If the design is compliant it would be better to advertise the main-range out through all the links towards the provider but only the specific ones (/30, /32) out of the link you want to receive the traffic from, only in this way you will be 100% sure about the Inbound traffic path.

Hope this helps,

Loris

[Meylaers Jan]

Hi,

the local pref is local to the router.

If you  configure neighbor A with a local pref of 100 and neighbor B with a local pref of 50 and you are receiving the exact same prefixes from the 2 neighbors in your database the router will prefer(install the routes in to the routing table) of the router with the highest local pref configured.  You can go more into detail when using a prefix-list/acl and route-map with a match/set statement. 

Jan Meylaers

[a.samuelsson]

local pref is not local to the router but it is only valid within the as.

Are you running ibgp och ebgp toward your mpls provider.

Normally it is ebgp any then your local pref in not valid.

You have to as prepend in combination with allow as or have the mpls provider to set the lp in their network