Influencing the routing path using BGP.

[nikhil.kulkarni]

I came across a requirement to achieve some routing preference using BGP with the service provider on the Internet.

We are having 2 Internet links from different service providers, Provider-A and Provider-B and both running BGP with us. The BGP is configured to send full routing updates. For a particular network say 1.1.1.0 /24 we want to prefer Provider-A as the preferred provider for incoming and outgoing traffic.

How best can this be achieved? For incoming traffic we can simply prepend the network 1.1.1.0 /24 with higher AS path out of Provider-B. Is it a general practice that Provider-B strip the prepends?

How can we work on the outgoing traffic? Route-maps?

Thanks,

Nik

[Reza Sharifi]

Is it a general practice that Provider-B strip the prepends?

no the provides don't strip the prepends. For incoming traffic to you as-path prepend should work fine.

As for outgoing traffic, you can use higher local pref for your local subnet to take let say provider-A

HTH

[nikhil.kulkarni]

Thanks for the input Reza, I am still wondering how will Local Pref help me influence outgoing traffic.

In this case traffic originatin from the local subnet i.e. 1.1.1.0 /24(as an example) destined to any network across the globe should also take Provider-A.

-Nik

[ccarreto]

Hi, 

normally outgoing traffic in BGP is manipulated by local-pref. But this is based on target IP addresses, not on source addresses.

Manipulation on source addresses could only be done by policy based routing.

www.cisco.com/c/en/us/td/docs/ios/12_2/qos/configuration/guide/fqos_c/qcfpbr.html

www.cisco.com/c/en/us/support/docs/ip/ip-routed-protocols/47121-pbr-cmds-ce.html

Regards, Celio