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2 Cisco 2951 routers as BGP edge for small AS


We have 2 ISP lines (100 and 50 Mbit/s), 2 Cisco 2951 with 4 Gb RAM (although I read that maximum memory for them 2,5 Gb sigh ). So there will be an eBGP and iBGP connection for each router.

The questions are: will these routers be able to handle full BGP tables? Or we should ask ISPs for partial updates? Or use full tables and set inbound prefix-lists to deny routes with long prefixes?

Thanks in advance


P.S. I will appreciate a design guide for multihomed bgp with 2 routers and load balancing across ISPs .

Everyone's tags (3)
Hall of Fame Master

2 Cisco 2951 routers as BGP edge for small AS


I would be a bit concerned about the 2951 processing 2 copies of the full Internet routing table. We do not know anything about your environment, but I suspect that if we found out more it is likely that there is not much benefit to you from receiving full Internet routes from either provider. I would suggest that it might be a good design for you to ask the provider on the 100 connection to send only the default route and to use local preference to prefer this route. And to ask the provider on the 50 connection to send you default and partial routes and use local preference so that at least this default route will function as backup to the route on the 100 connection. The partial routes received will direct some traffic over the 50 connection and the default route on the 100 connection will get the rest of the traffic. And you have failover if either of the providers experiences a problem.




Re: 2 Cisco 2951 routers as BGP edge for small AS


Indeed I think that we will not achieve much by using full bgp tables. Just thought if 2951 were able to process two bgp tables why not do it?)

Thanks for the response.


VIP Mentor

2 Cisco 2951 routers as BGP edge for small AS

Why not just test it? There are two ways:

1) Connect you router to the ISPs and see what happens.

Ok, the Internet communities don't really like people that connect to a global routing system whitout a plan what should happen ... ;-) So we better take the other option:

2) Download the routing-table from the internet, convert it and load it into your local routers and start playing.

The way how to do that is described in many blog-articles like the following:

(It's based on dynamips, but you can adapt it to a real router).

Don't stop after you've improved your network! Improve the world by lending money to the working poor:

Hall of Fame Guru

2 Cisco 2951 routers as BGP edge for small AS


If you did download full tables for each router then how would you want to load balance the traffic because presumably you would want to favour the 100Mbps line ? If you did then with all those routes how are you going to decide which routes go down one link and which go down the other. That's an awful lot of configuration for not much gain.

If the bandwidth was the same on both links then perhaps it would be worthwhile.

I think RIck's suggestion is a good one. Of course it depends on how much traffic is sent to the partial updates eg. if the partial updates included facebook, google etc. then you may find the 50Mbps link is overutilised but there are no guarantees with this sort of thing.


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