Which router for BGP? 2 x 100Mb and 1 x 1Gb

Unanswered Question
Apr 28th, 2009

Hi all,

We currently have a pair of internet links one is 100Mb and one 10mb using hsrp between a pair of 2821 routers and the same isp. We're moving to multiple ISP's and dropping the 10Mb link to have 2 x 100Mb and 1 x 1Gb link from 3 providers and using BGP.

We want to run multiple VPN sessions from customers and between our sites plus hosting some remote backup solutions which use circa 100Mb and may burst to 400Mb overnight for periods.

Having had discussions with various providers we've been recommended difering routers from each provider, starting with smaller 3845 going to 7206 and then ASR 1002.

Can someone quantify how we should look to size a router. We'd like limited routing information for UK based destinations and then defaults to elsewhere if thats possible.

thanks

AC

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Collin Clark Tue, 04/28/2009 - 12:33

Looking at the performance guide (see attached), the 7200 is a viable option and so is the ASR. I like the 7200's they have a stable IOS and good features. I have not had a chance to use the ASR so I can't really comment on them.

Hope that helps.

Joseph W. Doherty Tue, 04/28/2009 - 13:30

The performance reference that Collin provided, goes far in helping to "size" a router. If you look at the Fast/CEF Switching Mbps column, that will give you an idea of the bandwidth the router can forward. Keep in mind, though, to allow for duplex traffic, and to allow sufficient reserve extra capacity. For the latter, you might want to try to insure the expected CPU won't average more than half to two thirds.

Also keep in mind actual expected load and impact of other processes. I.e. you don't always needs to size for maximum link bandwidth, although doing so, guarantees performance if the link goes to 100%. In your case, processing Internet BGP tables and/or VPNs (if terminated on the router), needs careful consideration (NB: partial Internet BGP do help to reduce CPU BGP scanner load).

For example, the 3845 notes 256 Mbps. Halving that for duplex, and again 50% for reserve capacity, it would probably "safely" support 64 Mbps (duplex). I.e. 3845 could be slightly insufficient to support 100 Mbps (and probably why Cisco recommends it for up to T3s [45 Mbps].)

The G1 or G2 variants of the 7200 (or 7301) would be better positioned for 100 Mbps. (If you don't need the slots, don't overlook the 7201/7301.)

For Gig, you'll probably want to consider the ASR or perhaps a 7304 with NSE-150.

Depending on your feature needs, you might want to investigate the Metro Etherswitches (NB: VPN and memory for BGP might be issues).

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