Reducing BGP Memory using filter lists

[jeff]

I have a Cisco 7206 router that is connected with multiple T1s to multiple Internet carriers. We are running BGP 4 to the three carriers. The router is using IOS version 12.1(17). A recent problem brought to my attention the need to optimize the memory of the router. One suggestion was to optimize the memory being used by BGP. It was suggested that I use the article below to help optimize the memory used. By coincidence the memory examples in the article are very close to our current configuration. I'm not too familiar with BGP and it's configuration. I would like to apply an inbound filter list for BGP but I would like to make sure I'm not going to affect our routing. I have included our BGP configuration minus the sensitive information.

I would appreciate any help with configuring an inbound filter list for our router.

Thank you,

Jeff

http://www.cisco.com/en/US/partner/tech/tk648/tk365/technologies_tech_note09186a0080094a83.shtml

router bgp xyz

no synchronization

bgp log-neighbor-changes

bgp dampening

network xxx.yyy.0.0 mask 255.255.192.0

neighbor yyy.yyy.yyy.yyy remote-as A

neighbor yyy.yyy.yyy.yyy route-map G-in in

neighbor yyy.yyy.yyy.yyy route-map G-out out

neighbor zzz.zzz.zzz.zzz remote-as B

neighbor zzz.zzz.zzz.zzz ebgp-multihop 2

neighbor zzz.zzz.zzz.zzz update-source Loopback0

neighbor zzz.zzz.zzz.zzz route-map S-IN in

neighbor zzz.zzz.zzz.zzz route-map S-OUT out

neighbor xxx.xxx.xxx.xxx remote-as C

neighbor xxx.xxx.xxx.xxx route-map C-IN in

neighbor xxx.xxx.xxx.xxx C-OUT out

no auto-summary

!

ip as-path access-list 10 permit ^$

ip as-path access-list 11 permit .*

ip as-path access-list 20 permit ^$

ip as-path access-list 21 permit .*

ip as-path access-list 30 permit ^$

ip as-path access-list 31 permit .*

!

route-map G-out permit 30

match as-path 30

!

route-map S-IN permit 11

match as-path 11

!

route-map C-IN permit 21

match as-path 21

!

route-map S-OUT permit 10

match as-path 10

!

route-map C-OUT permit 20

match as-path 20

!

route-map G-in permit 31

match as-path 31

[steve.barlow · Accepted solution]

Your outbound filters are correct. A good filter to save memory is to accept the default route from each of your ISPs plus the ISPs routes and it's directly connected AS routes.

For example your route-maps inbound:

route-map S-IN permit 10

match as-path 1

!

route-map G-IN permit 10

match as-path 2

!

route-map C-IN permit 10

match as-path 3

!

ip as-path access-list 1 permit ^x_[0-9]*$ (where x is one ISP's AS number)

ip as-path access-list 2 permit ^y_[0-9]*$ (where y is one ISP's AS number)

ip as-path access-list 3 permit ^z_[0-9]*$ (where z is one ISP's AS number)

Hope it helps.

Steve

[jeff]

Steve,

Thanks for the reply. I did notice that for the outbound I can use the same list (or number) since all three are using the same expression. The inbound should be individually defined with your suggested lists? I just found a Cisco tech doc on expressions, hope this will help me understand the expressive characters. I will probably need to read up on the route-map command.

Thanks again for the help.

Jeff