BGP Cond Advertisement - Is it possible to age historical RIB entries?

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May 16th, 2007
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I'm configuring a conditional advertisement configuration to control route advertisement and to provide redundancy. I've configured the system correctly, I can fail the system/fail back with no issues. I know that BGP does not act upon the condition until the

the non-exist address has aged from the RIB table. Under default conditions its taking the RIB table 120s after receiving the 'rcv UPDATE' notification from its peer to age the historical entry out. Is there a way to age the entry faster? In combination with this I'll be configuring route dampening to control flapping. I would like the BGP process to react faster to the change (20s or so). BGP scan time has been reduced to 5s. This process is being run on a 3750, I mention this as I know the command feature set is not as rich as on a router. The other side of this configuration is the identical. Any suggestions would be appreciated.


router bgp 2222

no synchronization

bgp router-id 10.30.254.4

bgp log-neighbor-changes

bgp dampening 1 750 3000 4

bgp scan-time 5

network 10.30.254.4 mask 255.255.255.255

redistribute ospf 20 route-map remote2bgp

neighbor 10.30.2.21 remote-as 2221

neighbor 10.30.2.21 ebgp-multihop 4

neighbor 10.30.2.21 update-source GigabitEthernet1/0/1

neighbor 10.30.2.21 soft-reconfiguration inbound

neighbor 10.30.2.21 advertise-map ADVERTISE non-exist-map NON-EXIST

no auto-summary


***debug ip bgp updates output****


*Mar 1 10:17:40.419: BGP(0): 10.30.2.21 rcv UPDATE about 10.30.255.4/32 -- withdrawn

*Mar 1 10:17:40.419: BGP(0): no valid path for 10.30.255.4/32

*Mar 1 10:17:40.419: BGP(0): nettable_walker 10.30.255.4/32 no best path

*Mar 1 10:17:44.932: BGP(0): no valid path for 10.30.255.4/32

*Mar 1 10:17:49.940: BGP(0): no valid path for 10.30.255.4/32

*Mar 1 10:17:54.948: BGP(0): no valid path for 10.30.255.4/32


****output supressed****


*Mar 1 10:19:35.108: BGP(0): no valid path for 10.30.255.4/32

*Mar 1 10:19:40.116: BGP(0): no valid path for 10.30.255.4/32

*Mar 1 10:19:50.132: BPG(0): Condition NON-EXIST changes to Advertise

*Mar 1 10:19:50.132: BPG(0): Condition NON-EXIST changes to Advertise

*Mar 1 10:19:50.132: BGP(0): net 10.29.1.0/24 matches ADV MAP ADVERTISE: bump version to 31

*Mar 1 10:19:50.132: BGP(0): net 10.29.255.3/32 matches ADV MAP ADVERTISE: bump version to 32

*Mar 1 10:19:50.132: BGP(0): net 10.29.255.4/32 matches ADV MAP ADVERTISE: bump version to 33

*Mar 1 10:19:50.132: BGP(0): nettable_walker 10.29.1.0/24 route sourced locally

*Mar 1 10:19:50.132: BGP(0): nettable_walker 10.29.255.3/32 route sourced locally

*Mar 1 10:19:50.132: BGP(0): nettable_walker 10.29.255.4/32 route sourced locally

*Mar 1 10:19:50.132: BGP(0): 10.30.2.21 10.29.255.4/32 matches advertise map ADVERTISE, state: Advertise

*Mar 1 10:19:50.132: BGP(0): 10.30.2.21 send UPDATE (format) 10.29.255.4/32, next 10.30.2.22, metric 2, path Local

*Mar 1 10:19:50.132: BGP(0): 10.30.2.21 10.29.255.3/32 matches advertise map ADVERTISE, state: Advertise

*Mar 1 10:19:50.132: BGP(0): 10.30.2.21 send UPDATE (prepend, chgflags: 0x0) 10.29.255.3/32, next 10.30.2.22, metric 2, path Local

*Mar 1 10:19:50.132: BGP(0): 10.30.2.21 10.29.1.0/24 matches advertise map ADVERTISE, state: Advertise

*Mar 1 10:19:50.132: BGP(0): 10.30.2.21 send UPDATE (prepend, chgflags: 0x0) 10.29.1.0/24, next 10.30.2.22, metric 2, path Local


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mbadali Wed, 05/16/2007 - 10:53
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Stare at things long enough they begin to make sense! The dampening statement is obviously causing the historical entry to be created. I'll be focusing on the dampening aspects to control flapping and to tune the conditional advertisement. Removing the dampening statement caused the conditional advertisement to be invoked 30-60s after the withdraw notification which is in line with what Cisco says.

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