3725 BGP and ram

Unanswered Question
Mar 3rd, 2008

Hi all,

I've got a couple of 3725 that takes care of multihoming with bgp to my internet connections, each router peers with a different isp and the two peers to each other via ibgp.

Both are managing the full routing table and lately they have become to have memory issues, in fact a "sh mem" shows that both router have as little as 1M out of 256M of free mem.

Providing that the 3725's cannot hosts more memory, is there any hint in order to use less memory and therefore avoid to buy two new routers?



I have this problem too.
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Danilo Dy Mon, 03/03/2008 - 11:11


Ask your upstreams to advertise only partial internet route to you not full internet route. For example, your upstream provider can advertise its own route plus routes coming from directly connected neighbors, plus a default route to reach the rest of the Internet.

You can also do it yourself, for example in this link http://www.cisco.com/warp/public/459/26.html#t5 ASN4 is your upstream ASN, then add a default route



Massimo Baschieri Mon, 03/03/2008 - 12:12

Hi Danilo, tnx for your kind reply.

Your suggestion is very straightforward and simple to apply, but in my understanding this way I greatly loose the capability to load balance between the two connections, am I right?



Richard Burts Mon, 03/03/2008 - 13:35


We do not know how much you have been able to spread your traffic by having full routes from both providers. But it seems to me that there is a choice that you need to make: you can keep the existing routers, avoid the expense of replacement, and you may need to give up some load balancing. Or if the load balancing is important then you may need to spend the money to get new routers that can work with the reality of the large size of the Internet routing table.

So which is more important: do you save money and give up some load balancing, or do you keep load balancing and spend some money? I am not sure that you can have both.



Joseph W. Doherty Mon, 03/03/2008 - 21:22

If your primary concern is outbound load balancing, you're probably best served by having two default outbound routes.

One thing having the Internet tables provides is optimal path selection, usually at least from an AS hops view. Moving to partial tables will move you away from the foregoing optimal path selection. How it impacts your current load balancing could be neutral, better or worse.


Personally, I'm an advocate of Cisco's OER/PfR technology. It can dynamically analyze end-to-end performance and dynamically analyze your link utilization. It can then shift routes to obtain the best dynamic performance. The technology might be a bit early for most to adopt, but something, at least conceptionally, you might want to become familiar with.

bmcginn Mon, 03/03/2008 - 16:16


You could always buy a memory upgrade. I run two 3825 routers doing the same setup as you and with the 512Mb upgrade, they're doing fine. If the 3725's can get a memory upgrade, it may be cheaper than full router replacement costs. Although they don't have the throughput of the 3800 series, I assume the 3725's will be able to handle it also.

Also, as the other posts have mentioned, having your upstreams advertise only the partial Internet routing table with more than likely help too.


Massimo Baschieri Tue, 03/04/2008 - 12:05

Hi Brad,

unfortunately, at least reading the device data sheet, 256M of dram is the maximum for the 3725 router, that was my first thought.

It seems that I need to buy two new routers or get rid of the full internet table.




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