Best Router for Multihomed BGP

Unanswered Question
Oct 10th, 2008

Hi all,

I have not configured BGP before and I need to find out the best one router solution for 2 provider multihomed BGP. My client has already received an ASN and is ready to proceed with the two ISP's in agreement. They want to use BGP for the normal reasons. Always up from the outside. They have about 200 users on the LAN and the router must terminate 2 T1 circuits. Would a 1841 be able to do this. Or should I be looking at the 2800 series? Specific models and line cards would be helpful. Thanks!


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royalblues Sat, 10/11/2008 - 00:14


An 1841 router with VWIC-2MFT-T1 card would work fine as long as you make sure you do not receive the full internet routing table from the internet.

You can also consider the 2800 series router which supports the 2nd generation VWIC cards.

If you plan to receive the full routing table, i would suggest you atleast go with a 38xx with minimum 256 Mb RAM.



Joseph W. Doherty Mon, 10/13/2008 - 17:05

What router you might need depends much on whether you intend to accept two full size Internet routing tables. Besides sufficent RAM, the BGP scanner process will use lots of CPU while scanning two full Internet routing tables. If you only pass your AS's network to your ISP peer's and accept defaults from them, an 1841 might suffice. (This also assumes the 1841 supports BGP.) Otherwise as Narayan suggests, you might need at least a 38xx. (I would suggest even more RAM for two Internet tables, say 512 MB, and might also suggest looking at the 3845, 7201 or 7301.)

kurtcarlson Thu, 10/16/2008 - 14:12


What if I were to get 2 1841's 1 for each provider and then run HSRP between them for a common gateway?

Also What is the advantage of taking a full internet routing tables over only accepting the defaults.

I want our servers to always be accessible from the internet in case of outage. I'm not too concerned about inbound load balancing. However outbound load balancing would be optimal.

Also outside vpn connections will need to remain up if there is an outage on one ISP. Both remote and site to site.



royalblues Thu, 10/16/2008 - 22:30

I think you will be good with receiving only the defaults from the provider.

With a full internet routing table from both the providers, you will be able to choose the best path to reach a prefix. If you run HSRP and receive only defaults, there will not be any outbound loadbalancing.

And the most important thing is to have your own address space from an ARR so that both providers accept to route it and provide high availabilty.



mheusing Thu, 10/16/2008 - 22:55

Hi Kurt,

The Design and implementation of a high availability internet access solution is not that simple as to give a complete answer in a posting. Thus I would recommend you to start reading some of the following documents:

"Single Site Multi Homing"

"Connecting to a Service Provider Using External BGP"

"Internet Edge Design Architectures SRND"

Once you have identified with the customer all requirements - amongst which also cost is important - you can choose a proper design from e.g. the SRND and then pick the hardware.

As a rule of thumb: 512 MB RAM for full internet table and decent CPU, like a 7200 with NPE-G1/G2.

Last hint: the ISPs your customer is peering with might help you ... at least you have to talk to them about the BGP peering - full, partial, only default route - and which hardware they would suggest.

Hope this helps! Please use the rating system.



patrickvanham Fri, 10/17/2008 - 00:12

I have to agree with Martin here, there are many questions unanswered. The choice of router is also going to be based on what is planned for the client side, how much load is going to be placed on the interfaces, whether you can use use cef or have to with process based switching, whether or not packet inspection and/or NAT will be performed.


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