BGP Route Selection question

[Colin Higgins]

I have a router with 2 WAN (MPLS) connections to two different IPSs.

One connection is a 3mbs MLPPP connection and the other is a 10mbs MetroEthernet connection.

Both use BGP to peer up with the ISP with private AS numbers (65001, 65002, etc)

I want the router to always prefer (use) the BGP connection through the 10mbs link, but here are my considerations:

I can't change the prefeix length for the peers. In other words, BGP 65001 is going to advertise 192.168.21.0 /24 to its peer, and BGP 65002 is going to advertise the same network with the same mask.

What is the best way to make sure the 10mbs link is always preferred? Can I do local preference?

Any advice here would be appreciated.

[shehinpm1 · Accepted solution]

Hi Colin,

LP will be the best option to achive,bcoz LP determines the best path for OUTBOUND traffic,using MED

we can determin the way to our AS

[Colin Higgins]

would the

bgp default local preference ...

command under peer configuration for AS 65002 (10mbs link)

affect all networks advertised? In other words, if I have 50 subnets, the LP would be applied to all of them?

[cisco_lad2004]

Correct ! this would change it from default value of 100

[cadet alain]

hI?

you could also use weight as this is a cisco router and you've got no iBGP peerings.

Regards.

Alain.

[cisco_lad2004]

Colin,

As previous posters stated, use LocPrf for outbound traffic. You should also prepend your prefixes outbound towards the less preferred peer. This will ensure traffic comes back over desirable link.

HTH

Samir

Sent from Cisco Technical Support iPad

[Marwan ALshawi]

Hi Collin

As suggested by other posters above you can use local preference or wight for outbound and med for inbound

But now you thinking about this site only however aim assuming you have other site that need to communicate with the advertised prefix by this router over the two ISPs

So what you need to do is to think about the outbound direction and the returning traffic as well

So if want the communications to be all over one ISP as a main path you local preference to effect this increase it in the inbound direction from the preferred peer using route map

In the outbound direction to effect how other sitesnwill com to you network use as-path prepending but you need to check withnyour ISP that they allow and accept the AS prepending and increase the as-path over the backup/less preferred ISP by adding more AS numbers to the path using rout-map and apply it toward that bgp peer in the outbound direction

Be aware that you need to use same concept in your other bgp sites with two ISP links to avoid asymmetrical routing

Use the bellow link for more detail how you can configure the above

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml

HTH

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