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2 dedicated circuits into one router and BGP

jonesl1
Level 1
Level 1

Hey everyone,

Hoping you can give me a hand.   I have two seperate circuits (A full T1 and a fractional T1 512) coming into a single router.   The IP range for

the LAN is 192.16.1.X  /24.    Our telco is doing an AS override on our BGP number which makes all of our AS#'s the same at all of our

remote sites.   

Here is my dilemma.

One of the circuits is to be used for traffic destined for a certain group of IP addresses (determined by ACL) yet everything else will be going across the other circuit.   Previously this worked fine when we had two frame-relay circuits in there by way of policy routing.   However, now that we are doing BGP, I'm having some issues.   Since there are two circuits involved, I'm going to have two neighbors that are pointing to the telco.   So I'm not sure how to do this since I'm pretty sure it makes no sense to have two instances of BGP on one router, each with it's own neighbor.   Not to mention Im not even sure thats possible.....and then to top it off....they will have the same AS#.   See my confusion???   Ever seen a grown man cry???   I'm fixin to show ya!!!

So, if you guys can tell me how to go about this, I would greatly appreciate it......I'm at a loss.    Thanks in advance....you guys are awesome!!!

By the way, I don't have any config yet as I'm just now in the design phase of this.....so I have no configs to post.....still researching answers.

5 Replies 5

shaijo.mohan
Level 1
Level 1

If I have understood the requirement correctly, you have two link to the same ISP. And you want to have one as the preferred path for the traffic to group of IP. You can do this with the help of BGP attributes. I presume that you are going to have the eBGP connection on the interface rather than on the loopback.  In that case you can configure better local preferance for the set of IP you want and apply it to the neighbour.

Regards

Shaijo

Actually these aren't really going to an ISP as we are not getting internet over them.   They are just dedicated point to point connections.   And the traffic is being split because there are two departments on the remote side lan, but yet they use the same ip address scheme.   This is why i'm trying to split the traffic by destination, rather than source. 

Hi

Couple of questions.

1.Will u be running EBGP between your service providers.

2.U need to use a single AS number on ur router where these circuits will be terminated.The providers need to peer with u r AS number.

If you want the traffic from your side to prefer certain link for a particular ip address range then u can have local preference attirbute applied to that range.

It will be helpful if you can show us the topology with a simple graph.

Thanks

Yes, I will have EBGP with the service provider.

If I use a single AS number, how do I specify one neighbor for the first circuit and another neighbor for the second

circuit?  For instance, if Circuit #1 had CER of 192.168.1.2 /30 and PER of 192.168.1.1, the neighbor would be 192.168.1.1 if this was the only circuit in this router.

Now add circuit number 2,  CER is 192.168.2.2 /30 and PER is 192.168.2.1, the neighbor for this one would be 192.168.2.1 if it is to use this circuit. 

So my issue is how to specify the neighbors.   In addition, for the return traffic, I will have to put the same networks

on both AS instances (same AS number).   So both circuits will be advertising the same network.  See my dilemma?

Do i need to dump these two AVPN circuits and order a bundled T1 multilink instead or what are my options.

Thanks in advance.

Hi,

U can have both the service providers configured as your EBGP neighbors..this is call multi-homing which is normal.

Yes u can have multiple neighbot statements each for different neighbor.

You can control which networks are advertised to which neighbor using route-maps which is a powerful feature in BGP.

And it is OK if you adverrise the same networks to different providers,do your other locations will be having the links from both the providers.

Thanks

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