Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

BGP - 2 Carriers

I will be starting a new project to split the company WAN between two carriers. The corporate router will be connected to both carriers and is presently running BGP with existing carrier. When I install second serial link for other carrier, how do I configure BGP to push same subnets out two differenbt serial links?

Pardon my ignorance, but I'm just getting started in BGP




Re: BGP - 2 Carriers

Hello Ray,

in your scenario, you would need to configure load sharing. BGP selects only one best past to a given destination, so you cannot really load balance. Have a look at the link below, it provides a sample configuration for your setup:

Load Sharing When Multihomed to Two ISPs Through a Single Local Router




Re: BGP - 2 Carriers

You may need to obtain a public IP range (if you don't have it now). Because one ISP will not announce other ISP's subnet to Internet and the load-sharing may be achieved by out-going traffic only, because the return paths are not the same via two ISP to your company.

Or you can use one set of IP for ISP A and another set of IP for ISP B then backup each other.

Hope this helps.

Re: BGP - 2 Carriers

Hi Jack,

Just one more thing, what if we dont have BGP or any other dynamic routing protocol and have only static routes?


Wilson Samuel


Re: BGP - 2 Carriers


I don't mean to correct Jack's post above (lowly CCNA correcting a CCIE), but you can advertise the subnet out both ISPs. Both providers will give you an IP scheme. You then can have your primary ISP give written consent to your secondary ISP to advertise out the subnet. This will provide inbound redundancy. The configuration is not the issue here, rather it's the coordination between the telecom providers. We do this with PaeTec and Time Warner and have had great success. This means that traffic destined for our subnet travels in over either provider. If outside customer A is closer to Time Warner POP and customer B is closer to PaeTecs POP, they'll travel over their respective carrier. This does not cause Internet routing issue as both routes will be received by all upstream providers, but the one with the best metric will be preferred over the other. Not many telecom companies will tell you this is available to do... but ask you shall receive. Any more questions let me know.


CreatePlease to create content