Local Pref. for sub_interfaces in cisco router

[Danty]

Hi.... I have 2 routers are connected via one link, in my experiment each routers represents one AS. If this link is subdivided into 2 sub interfaces, can I assign a local Pref. for each sub interface? The idea is that I should have 2 different networks (Autonomous Systems) and they should be connected with 2 links, and then I control the traffic of the update messages to go through one link by changing the local Pref. value. 

Any help would be appreciated.

[Richard Burts]

Depending on the type of connection it is probably ok to configure subinterfaces and to create 2 connected subnets. But in configuring BGP your router can have only 1 AS number. So I do not see how what you are suggesting about local preference could work.

HTH

Rick

[Danty]

The idea is to implement the two routers as if they were 2 ASes with 2 routers in each AS and there is 2 links between the ASes. So if each router represents an AS, then I have to make the link between them 2 links (by sub_interface ). This way we created the topology. The test going to be:  is making BGP attack from a third AS (router) to change the Local Pref. of one of the two ASes  to a higher value than 100 (by adding the TE community 2:2000  to the BGP update/prefix)  to make the prefixes announcements to go out of the second link of that AS to the other AS.

[Sebastian Fernandez]

Hi Danty,

You can use VRF to achieve your results. Configure different sub-interfaces in different VRF and run a BGP for each VRF using local-as to present yourself originating in a different AS.

something like below, only posting an idea of configuration

ip vrf A
  rd 1:1
ip vrf B
  rd 2:2

interface Gi0/0.1
  ip vrf forward A
interface Gi0/0.2
  ip vrf forward B

Router bgp 100
  address-family ipv4 vrf A
    neighbor A.A.A.A remote-as AS1
    neighbor A.A.A.A local-AS 100
  address-family ipv4 vrf B
    neighbor B.B.B.B remote-as AS2
    neighbor B.B.B.B local-AS 200

Hit me up with Star if you find this helpful.

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Sebastian

[paul driver]

Hello @Sebastian Fernandez 

I think the OP is suggesting they want Two ASN's on the same router which isnt viable

@Danty  Can you please post a topology on what you are trying to achieve

[Sebastian Fernandez]

Hi @paul driver 

That's right BGP does not allow more than one AS on the router. However, for presenting different AS to different peers 'local-as' is an option and when used in a VRF context, it almost makes it appear as a another AS on the BGP on a different virtual router(routing) instance. But anyways local-pref won't be forwarded out to eBGP peer.

If @Danty can provide more details with topology he wants to achieve, we all can contribute further with more suitable options/suggestions.

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Sebastian

[Danty]

It is not implementing 2 ASs on the same router , it is one AS per router but as if this as has 2 internal routers each with a local pref. value. so instead of having 2 ASs with routers routers in each AS and 2 connections between the ASs , I have only 2 routers to implement this network. I attached the diagram, the one above is the network we should implement with only 2 routers connected via one physical link. 

So as in the Diagram, Router B should be AS1 and Router A should be AS2 and idea to be able to implement the one physical link as if it were 2 links running eBGP and each of those to link ends with a different local pref value in the AS.