BGP table memory requirements on a 2800

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Sep 11th, 2008
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I've got a 2821 that is choking on my ISP's BGP table. But everything I see online indicates that I have enough memory. I understand that CEF uses the same space on the DRAM as the BGP table, but that CEF doesn't use much space. A sh ver output:


Cisco 2821 (revision 53.51) with 251904K/10240K bytes of memory.


I'd like to know what the two numbers indicate, and if it's possible to reallocate the memory. Any other light that someone can shed will be helpful.

Correct Answer by merryllem about 8 years 9 months ago

Just to add something Terry's comment. If you are not advertising anything special to you ISP. The easiest solution would be just to remove BGP and configure a static default route, Since there is really no use for BGP at this point.

Correct Answer by Richard Burts about 8 years 9 months ago

Terry


When you look at the numbers in the show version they tell you how much memory for main processing/how much memory for I/O packet processing. You add them together to get the amount of memory in the router. And it looks like your 2821 has 256 MB of memory.


You tell us that you are running BGP with your ISP but you do not tell us what the ISP is advertising to you. Based on the symptoms that you describe I will make a guess that the ISP is advertising the full BGP table to you. And I will suggest that your 2821 does not have enough memory to do that. I am not clear what you have been looking at on line, but what I see generally says you should have 512 MB to process full BGP tables.


If I am correct in understanding your problem there are several alternatives that you can consider to reesolve it:

- upgrade memory on the 2821.

- replace the 2821 with a stronger router with more memory.

- negotiate with your ISP so that they do not advertise the entire BGP table.


If you are single homed (connected to a single ISP) then I see little advantage in receiving the full BGP table from them. If they advertise just a default route (or perhaps a default route and their directly connected customer routes) then you have plenty of memory - and enough content in your routing table to process what you need.


HTH


Rick



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Correct Answer
Richard Burts Thu, 09/11/2008 - 18:39
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Terry


When you look at the numbers in the show version they tell you how much memory for main processing/how much memory for I/O packet processing. You add them together to get the amount of memory in the router. And it looks like your 2821 has 256 MB of memory.


You tell us that you are running BGP with your ISP but you do not tell us what the ISP is advertising to you. Based on the symptoms that you describe I will make a guess that the ISP is advertising the full BGP table to you. And I will suggest that your 2821 does not have enough memory to do that. I am not clear what you have been looking at on line, but what I see generally says you should have 512 MB to process full BGP tables.


If I am correct in understanding your problem there are several alternatives that you can consider to reesolve it:

- upgrade memory on the 2821.

- replace the 2821 with a stronger router with more memory.

- negotiate with your ISP so that they do not advertise the entire BGP table.


If you are single homed (connected to a single ISP) then I see little advantage in receiving the full BGP table from them. If they advertise just a default route (or perhaps a default route and their directly connected customer routes) then you have plenty of memory - and enough content in your routing table to process what you need.


HTH


Rick



Correct Answer
merryllem Thu, 09/11/2008 - 18:46
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Just to add something Terry's comment. If you are not advertising anything special to you ISP. The easiest solution would be just to remove BGP and configure a static default route, Since there is really no use for BGP at this point.

angrynetguy Fri, 09/12/2008 - 05:31
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Thanks, folks. We're moving data centers, from something I merely inherited. The old place just had a static route. I think, rather than throw more money at the problem, we'll go back to static routes. As for what I was seeing online, the clearest answer I could find was from Cisco, but the page copyright date was 2002. It said 256 MB. I was afraid it might be out of date.

Richard Burts Fri, 09/12/2008 - 08:06
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Terry


In 2002 it was adequate to have 256 MB and be able to process the Internet routing table. But the Internet routing table is now very much larger.


There are several options that you might consider. If you are single homed (connected to a single provider) then a static default route will work. This is the most simple and lowest overhead solution. If you want something a bit more sophisticated and flexible then you could run BGP with the provider and have them advertise to you only a default route. The advantage of this is that if there is some problem in their network upstream from you then they could withdraw the advertisement and you could know not to use resources to forward to them if the traffic will just be dropped.


Thank you for using the rating system to indicate that your question was resolved (and thanks for the rating). It makes the forum more useful when people can read a question and can know that there were responses that did resolve the question.


HTH


Rick

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