Maximum BGP table size in ISR 4551 & 4331 with standard data plane DRAM (2 GB)?

[ThomasKlausen]

The headline says it, really.

We're running an MPLS network using BGP for routing and the number of prefixes in our routing table is set to increase considerably, for boring and irrelevant reasons. I can't seem to find a definitive source listing a maximum number of prefixes for the ISR 4551 and 4331 with the default 2 GB of DRAM - does anyone posses this information?

Please feel free to ask follow-up questions, if needed.

Best regards,

Thomas

[Philip D'Ath · Accepted solution]

You wont find a definitive number, because it depends on a number of factors as to how much memory each prefix needs (such as community attributes, etc).  It also depends on weather other router features are chewing up RAM.

If the routers memory is not being used for anything else, I would say it should be reasonably safe up to 1.2 million prefixes.  You can also expand the routers memory ...

As a general rule, I say you need 1GB of RAM for every 750,000 or so prefixes.  You also need to leave a bit of memory left over for the router itself.

Your mileage may vary.

[Jose Jara]

Hi,

The 4400´s and 4300´s series uses different memory distribution. In the 4400`s series exists a separation for the control plane and the data plane memory. By default, 2 GB for data plane and 4 GB for Control Plane. You need at least 8 GB for the control plane to support BGP full routing. On the other hand, the 4300´s series the memory is combined for both data plane and control plane. Also, you need at least 8 GB of DRAM.

Hope this helps,

Jose.

[Philip D'Ath]

Good answer - but back to the original posters question - what do you think is the prefix limit?

The original poster talks about their MPLS network, so I don't think they are talking about the full Internet BGP routing table.

[ThomasKlausen]

Good responses, thanks!

I should have been more exact, apologies. Neither the route table (as is) nor the expansion is in the hundreds of thousands - looks like we may be going from about 3,000 to about 6,000, give or take.

From the replies, it looks like we will have room to spare.

Thanks very much!

Thomas

[Philip D'Ath]

You will have no issues.  It would be great if you could rate helpful responses and mark answers as correct.  :-)

[ThomasKlausen]

Perfect, thanks. Rates and marks coming all y'all's way.

[gkuchera]

I have a couple of stock 4451's running >100k routes with no issues.  Partial Internet routes.

I did however crash one when I tried to pull full tables on it,  its crashed at about 700k routes given or take 10k.  

Geoff

[sandeepk]

what is best practice to have partial routes from ISP...

Do we receive all and then filter before adding to routing table. Suppose we need only /16. Filtering itself takes some resources and not sure if it is ideal way.

OR 

ISPs agrees to send partial routes only as per our requirement. Suppose if we need only default + ISP AS local routes.

[Giuseppe Larosa]

Hello @sandeepk ,

>> ISPs agrees to send partial routes only as per our requirement. Suppose if we need only default + ISP AS local routes.

Yes usually there is an agreeement on what the ISP will send to you.

However, you can use appropriate route filtering on your side.

Hope to help

Giuseppe

[Joseph W. Doherty]

Either - wouldn't worry too much about resources needed for filtering.

If you filter youself, you don't need to insure your ISP does it "right".

If you do filter, and take full Internet set of routes, you may want to insure your router, and ISP's, will use full MTU.