BGP maximum-prefixes

[cklam]

In the last week, our WAN routers have seen spikes in BGP prefixes at around 5 am EST. But, for the last two years, we have seen only an average of 224,700 prefixes. So, why the spike? Also, what do people recommend we increase the limit to? In the meantime, I have set the restart to 20 minutes.

See example, below

Aug 24 04:48:20 XXX.XXX.XXX.XXX 286707: Aug 24 04:48:12.564: %BGP-3-MAXPFXEXCEED: No. of prefix received from ZZZ.ZZ.ZZZ.ZZZ (afi 0): 225001 exceed limit 225000

Thanks,

Chris

[Pavel Bykov]

Internet is growing, and so is the number of prefixes. Two years ago it was around 190000 If I remember correctly.

Maximum-prefixes command is created to limit routes from customers and configuration errors. So You should implement it for precise control. All internet routes are most routes you can receive anyway, unless there is bad configuration and number of routes double.

I'd recommend setting the limit to around 240K for peerings where you are exchanging complete routing tables, and create a warning around 235. Then use warning as a reminder to increase the limit again.

It will constantly grow until there will be mandatory migrations to IPv6, then it will grow slower, but it will still grow for a while.

Hope this helps.

Please rate all helpful posts.

[cklam]

Thanks! What do you think the restart value should be? As it took nearly thirty minutes for the prefix spike to go below my threshold, I was planning on resetting the value to 30.

[Pavel Bykov]

Usually the restart value is set to one hour. Which should be ok in your case.

But remember, maximum-prefixes limit is to limit failure impact or block misconfiguration of your peer. It is not suppose to disrupt your routine operations - so you should not see resets at all during normal operation! Set it to the limit that is reached only in case of a problem.

Hope this helps.

Please rate helpful posts.