BGP table size

[jagdev.dhaliwal]

Hi All,

Please help me to calculate the BGP table size in terms of memory required, I got the information from looking glass. Guide my which components i need to add and than calculate the memory size required.

BGP table version is 262538329, main routing table version 262538329

454321 network entries using 53155557 bytes of memory

908642 path entries using 47249384 bytes of memory

98794/69504 BGP path/bestpath attribute entries using 12250456 bytes of memory

51 BGP rrinfo entries using 1224 bytes of memory

86096 BGP AS-PATH entries using 2220164 bytes of memory

70 BGP community entries using 1924 bytes of memory

20 BGP extended community entries using 496 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 114879205 total bytes of memory

BGP activity 14224881/13758829 prefixes, 70150237/69218155 paths, scan interval 60 secs

If i would be multihomeing with two ISPs with full BGP table and than how should  I calculate the memory requirement for router?

Thanks In advance.

Jagdev

[Giuseppe Larosa]

Hello Jagdev,

there is a line with total memory used by BGP

>> BGP using 114879205 total bytes of memory

However, this is only a part of the story: CEF tables use quite a memory for each IPv4 prefix in addition to the memory used by BGP. ( 1 kbyte for each IPv4 prefix)

A BGP full table is around 420000 IPv4 prefixes

Your router should have at least 1 GB of RAM for multihoming as a safe assumption

Hope to help

Giuseppe

[jagdev.dhaliwal]

Hello Giuseppe

Thanks for your response,  Can you please guide me how should i calculate the memory, like you explained for CEF

454321 network entries using 53155557 bytes of memory would have required 454321kbyte for CEF, 

How much would for one BGP table and  other thing than which parameters would required double as there will be dual ISP and router would be learning the BGP information from two eBGP peers.

I want to understand the method to calculate it

Thanks

Jagdev

[Giuseppe Larosa · Accepted solution]

Hello Jagdev,

an exact calculation is not so important as memory chips come in discrete pieces (256 MB, 512MB, 1GB and so on)

However, you can make a reasonable guess by doubling the memory used by BGP for two BGP full tables ( it will be more then the effective use) and by counting only one the prefixes in the CEF table as only the best path goes in the CEF table.

Note also that the line you have mentioned is only the memory used for the IP prefixes not all the memory used by BGP

>> BGP using 114879205 total bytes of memory

and

>> 454321 network entries using 53155557 bytes of memory

AS paths and all other BGP attributes need to be stored too, as the various lines of the show output show..total memory used by BGP is the first line.

Hope to help

Giuseppe

[jagdev.dhaliwal]

Thanks Giuseppe,

I was not concerned about memory chips, i already going to get 1GB ones, but i wanted  to know how should i calculate the memory. If i am planing to implement it should know about this as much as i can.

Thanks once again.

JD