ISR 2821 as a BGP router: can it handle partial routes from ISP directly connected customers?

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Mar 17th, 2010
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Hi all,


I have a question about ISR2821 as a BGP router. Here is the info,

We have a customer currently having one ISP (20MB) with ISR2821 as edge router running BGP accepting only default route from current ISP. They will soon bring up another 100MB link from 2nd ISP. To better utilize both links, I want to do load sharing using BGP attributes (local preference and as-path prepend). To realize this, I want ISP to advertise their directly connected customers (partial routes) plus a default route.


The question is "can ISR2821 handle this", will 2821 have high CPU utilization and memory issue?

As default, 2821 has 256MB memory.


Anyone had experience in a similar situation?

Thanks!!!


PS: I am considering ISR G2 for the 2nd BGP router, ASR 1000 series may be a budget issue.

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milan.kulik Wed, 03/17/2010 - 12:22
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Hi,


IMHO, it's just a question of the number of prefixes received.

Currently, I have 2811 receiving  3000 prefixes from 3 neighbors, e.g.

And no problem.


router#sh ip bgp sum
BGP router identifier ...

BGP table version is 471805, main routing table version 471805
2999 network entries using 386871 bytes of memory
8984 path entries using 467168 bytes of memory
2982 multipath network entries and 5964 multipath paths
354/118 BGP path/bestpath attribute entries using 43896 bytes of memory
85 BGP AS-PATH entries using 2088 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 900023 total bytes of memory
BGP activity 43360/40361 prefixes, 270375/261391 paths, scan interval 60 secs


HTH,

Milan

fmjiang1966 Wed, 03/17/2010 - 13:08
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Milan,


Thanks!

In your case, the total memory used by BGP is less than 1MB (3,000 prefix).

I believe that even with big ISP, say Cogent, their directly connected customer prefix less than 40,000. Counting two ISPs, the prefix number will rise. 256Mb memory on 2821 might be enough. Although It may experience high CPU usage during bgp updates or neighbor establishment.

thanks again,


Fuming

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