BGP Multihoming with 2 ISP on single router

[Srijit Banerjee]

Hi,

We need to configure BGP multihoming with two upstream provider using only one router which will be acting both as Core and Edge Router.

Consider the following scenario:

Our ASN - 47117
Our Public IP Pools - 1.1.1.0/24, 1.1.2.0/24, 1.1.3.0/24, 1.1.4.0/24, 1.1.5.0/24

Upstream 1: (100 mbps)
ASN - 2222
IP: 5.5.5.0/30

Upstream 2: (200 mbps)
ASN - 3333
IP: 6.6.6.0/30

Our requirement:

Both the route must be active at the same time. Pass 1.1.1.0/24, 1.1.2.0/24 inbound and outbound traffic via Upstream 1 and 1.1.3.0/24, 1.1.4.0/24, 1.1.5.0/24 inbound & outbound traffic via Upstream 2. Incase of failure of any one upstream traffic must be automatically rotued via other one.

We receive only default route via BGP for both the uplinks.

What changes should I make to make the above scenario work?

[Amos Kafwembe]

Hi,

the link below is exactly what you need to do. hope it helps.

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/23675-27.html

-Amos-

[trfinkenstadt · Accepted solution]

Srijit,

I would probably do it something like this (check the attached file in notepad++ or wordpad):

You will have to do policy-based routing because you want 1.1.1-2.0/24s to go out upstream 1 and 1.1.3-5.0/24s to go out upsteam 2.  My as-path prepend will allow you to influence the path selection incoming to your network.  However, the recipients of the traffic could put the opposite policies in place and come back through the opposite provider.  You may wish to increase the number of as-path prepends in my configuration to try to influence this greater.

hth,

tim

[Srijit Banerjee]

Hi Tim,

I followed your steps and tested in GNS3. It worked perfectly. But I have some doubts. When there will be more upstream say 4 upstream, then is there a way I can specify the alternate route (which it takes after SLA track identifies upstream failures) as per my choice. 

Say, I have A,B,C,D as four upstreams. Now I have set next hop address of 1.1.1.0/24 to D and did SLA as u have done. Now I want to set priorities like, D Fails --> Changes to A --> A Fails --> Changes to C --> C Fails --> Changes to B.

Thanks a lot for your solution though. I was working with next hop only at the first but your concept of SLA implementation solved it.

 

Thanks,
Srijit B. 

My current Lab Topology -->

[Joseph W. Doherty]

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Posting

There are multiple approaches, and if you want to do proportional load balancing, things get more complex.  (BTW, Cisco's OER/PfR technology, might be considered for proportional, including dynamic, load balancing.)

If you want to try equal load balancing, the simplest approach might be to increase the number of routes paths BGP will place in the route table, from the default one to two, maximum-paths n, and use the secret/hidden command, bgp bestpath as-path multipath-relax, to use routes from different ASs.  See http://blog.alwaysthenetwork.com/tutorials/bgp-multipath-relax/

If you do the forgoing, you should see a default route to both providers.