Multihomed BGP hardware requirements

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Jun 4th, 2008
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I've been reading a lot of the posts regarding multihomed hw discussions both on mynetpro and other resources but there are a few things that I don't quite understand. I will start with describing our planned solution.

Two BGP routers will each peer (full table) with an from the other independent upstream provider. These two routers will also have an iBGP neighbor statement to the other.

We first were told (from on of our intended upstream providers) that two 2821 would be enough. These would be equipped with 1GB ram. We've also been in touch with a CCNP certified technician on another office who told us that this setup wouldn't be enough and he told us to go with (at least) something out of the 3800 series.

After I read some of the posts here concerning BGP hardware I see that the tcam on these routers isn't enough and that I should go for something like a 7201 or a 6500 and 720sup.

I've looked at some performance sheets from cisco and the difference in routing switching performance between process switching and CEF switcing is huge. For a 2851 for example it's 7.68 Mbps to 112.64 Mbps (process, cef). Is the difference really this big? Because according to some of the posts here that imply that you should go for a 7201 or similair, it's because the other doesn't have enough tcam to hold all the entries in the routing table that comes whit a full bgp table.

So my questions is (finally):

Can the 2851 handle a full bgp routing table and route traffic without dropping packets due to high cpu load?

Note: Our current internet connection is 30Mbit and we expect it to grow significantly within the nearest future.

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Overall Rating: 3.5 (2 ratings)
guruprasadr Wed, 06/04/2008 - 03:31
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HI, [Pls Rate if HELPS]

I don't recommend 2851 Router to handle the Full Internet Routing Table. Since today's Internet Routing Table Size is 2 Lac 48 Thousand.

In this case, you wll have Router Failure and CEF Services will get disabled if MALLOC Error observed.

So, recommendation is to, use beyond 3800 Series and for more better performance & future scalability use 7206 VXR Model with NPE G2 Card.

Attached is the Cisco Router Performance Measurement Data SHeet.

Hope I am Informative.

Pls Rate if HELPS

Best Regards,

Guru Prasad R

hannes.adollarson Wed, 06/04/2008 - 22:16
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Thanks for the quick reply. Regarding the CEF problem. Where can I find how many "entries" a 2851 for example can hold in it's tcam? Because as far as I've understand, it's when the tcam fills up that the routers switch to use process switching. Have I got this right?

guruprasadr Thu, 06/05/2008 - 01:14
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HI, [Pls Rate if HELPS]

Yes right. Normally, when the Processor cannot able to allocate required Memory for the CEF the MALLOC Failure Occurs.

In this situation, the CEF get disabled, the BGP Process are affected.

Best Regards,

Guru Prasad R

h.parsons Thu, 06/05/2008 - 12:39
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we are in a very similar situation as you but we will only receive a partial routing table. We are going to jump out on the bleeding edge and buying two ASR 1002 routers.

hannes.adollarson Mon, 06/09/2008 - 04:17
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Whats list price on those? We just bought and configured a new firewall cluster so we aren't to eager to pay for those kind of features.


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