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Multi-homed via 2 2620's with BGP-4 and 1 Class "C" Block

Fellow Networking Engineers,

I have a client that would like to utilize their 2 2620's via 2 different ISP's for redundancy and load balance/sharing with 1 Class "C" Block running BGP-4. What is a good design practice to achieve this solution? Any good links that will point me in the right direction would be very helpful. Also, any potential "landmines" to avoid?

New Member

Re: Multi-homed via 2 2620's with BGP-4 and 1 Class "C" Block

I think this is going to be more of a policy question than a technical one. I'll start with the basics, which you may or may not already know, but for the benefit of any others reading this.

To do BGP4 on the internet you must qualify for and obtain an Autonomous System number - usually from ARIN. This costs $500 per year, and you must be multihomed or about to be multihomed to get an AS. Ok that out of the way.

What I have found is that different ISPs will have different policies about BGP - what configurations they support & don't support, what kind of address block they'll do it with (a full Class C should be no problem).

To do BGP4 with a full route download, you'll need a router with lots of memory. I have been advised that a 2620 probably can't be upgraded with enough memory to do full BGP4. Each route map will have 140,000 or so routes. There are some links inside the TAC to estimate memory for BGP, as well as strategies for minimizing memory requirements.

I have heard some people mention having the ISPs simply download default routes and thus avoid the memory consumption, however this may or may not be something the ISP will support.

Load balancing is not automatic with BGP. There are a number of links discussiong load balancing & redundancy in this group, and in documents in the TAC. As far as I can tell at this point the two strategies are to break the full internet address space into blocks of networks & assign half to one router and half to the other, with backup routes in reverse. Alternatively you can do policy based routing to spread traffic inbound and outbound.

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