RE: [nsp] Help with BGP RAM utilization

From: Mark Borchers (mborchers@splitrock.net)
Date: Tue Dec 05 2000 - 10:47:51 EST


> Hi,
> with 3 "full table" upstreams I have this:
>
> 99861 network entries and 289325 paths using 20202078 bytes of memory
> 49353 BGP path attribute entries using 2569580 bytes of memory
> 42538 BGP AS-PATH entries using 1194776 bytes of memory
> 36746 BGP route-map cache entries using 587936 bytes of memory
> 57829 BGP filter-list cache entries using 693948 bytes of memory
> 11 received paths for inbound soft reconfiguration
> BGP activity 122127/3206009 prefixes, 535099/245774 paths,
> scan interval 15 secs
>
> If I increase this to, say 8 upstreams, how does this memory
> utilization
> increase, if I have soft inbound reconfiguration turned on for all?
>
> Does soft inbound mean the router keeps a full table for each
> neighbor?

From Cisco documentation:

How Much Memory Does Each BGP Route Consume?

Each Border Gateway Protocol (BGP) entry takes about 240 bytes of memory in
the BGP table and another 240 bytes in the IP routing table. Each BGP path
takes about 110 bytes.

Under normal circumstances, memory utilization depends on the following
three factors:

     number of prefixes (240 bytes per prefix)

     number of routes (240 bytes per route)

     number of alternate paths (110 bytes per alternate path)

As an example, let's say you're receiving 50,000 prefixes from four BGP
neighbors, and all of them make it into the routing table:

     BGP table: 50000 * 240 = 12,000,000 bytes

     Routing table: 50000 * 240 = 12,000,000 bytes

     Alternate paths: 50000 * 110 * 4 = 22,000,000 bytes

In this case, you'll need approximately 46 MB of RAM, not counting the RAM
needed to support Cisco IOS Software, Interior Gateway Protocols (IGPs),
and so on.



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