BGP scan timer
Hi,
Can anyone please explain me the concept of BGP scan timer? I thought the the scan is to be run every minute. But the debug show a scan running every 15 secs. I haven't changed the timer value from default.
R2#
*Mar 1 01:12:15.679: BGP: Regular scanner event timer
*Mar 1 01:12:15.679: BGP: Import timer expired. Walking from 1 to 1
R2#
*Mar 1 01:12:30.679: BGP: Regular scanner event timer
*Mar 1 01:12:30.679: BGP: Import timer expired. Walking from 1 to 1
R2#
*Mar 1 01:12:45.683: BGP: Regular scanner event timer
*Mar 1 01:12:45.683: BGP: Import timer expired. Walking from 1 to 1
Confused!!!
Comments
Ooops!! just now realized that default value is 15 sec for scan. [:D]
Oops..Just realized that the default timer for Import scanner is 15 sec..
what bgp scan-time shows? if u do not see it, must be default values of 60.
do sh run full | s router bgp
Its 60.
R2#sh run | sec bgp
router bgp 200
no synchronization
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 disable-connected-check
neighbor 1.1.1.1 update-source Loopback0
neighbor 3.3.3.3 remote-as 200
neighbor 3.3.3.3 update-source Loopback0
no auto-summary
R2#
But I assume that the one that runs every 15 sec is the import scanner which is related to VPNv4 routes.
Its 60.
R2#sh run | sec bgp
router bgp 200
no synchronization
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 disable-connected-check
neighbor 1.1.1.1 update-source Loopback0
neighbor 3.3.3.3 remote-as 200
neighbor 3.3.3.3 update-source Loopback0
no auto-summary
R2#
I assume that the one that runs every 15 sec in the import scanner which is related to VPNv4 routes.
R2#sh run | sec bgp
router bgp 200
no synchronization
bgp log-neighbor-changes
neighbor 1.1.1.1 remote-as 100
neighbor 1.1.1.1 disable-connected-check
neighbor 1.1.1.1 update-source Loopback0
neighbor 3.3.3.3 remote-as 200
neighbor 3.3.3.3 update-source Loopback0
no auto-summary
R2#
But a test done my me shows that BGP detects loss og next-hop in 15 secs.
R2#
*Mar 1 02:17:17.683: BGP: Regular scanner event timer
*Mar 1 02:17:17.683: BGP: Import timer expired. Walking from 1 to 1
Last scan ran at 02:17:17.683. Just after this I removed the IGP advertisement of next-hop route
R2#sh ip bgp
BGP table version is 4, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 100.0.0.0 1.1.1.1 0 0 100 i
R2#
*Mar 1 02:17:26.051: EvD: charge penalty 500, new accum. penalty 500, flap count 3
R2#sh ip bgp
BGP table version is 4, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 100.0.0.0 1.1.1.1 0 0 100 i
R2#sh ip bgp
BGP table version is 5, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* 100.0.0.0 1.1.1.1 0 0 100 i
R2#
HERE BGP DETECTED THE LOSS OF NEXT HOP AND MARKED THE ROUTE Out OF PATH SELECTION.
*Mar 1 02:17:32.687: BGP: Regular scanner event timer
*Mar 1 02:17:32.687: BGP: Import timer expired. Walking from 1 to 1
R2#
Totally confused now!
sorry, i meant if u do not see bgp scan-time configured; it means it likely default values of 60;
default vlaues/configs are hidden; u can see them with sh run full or all.
some new versions of ios have commands to make this event-driven event; other commands can infulence bgs walker to run.
Ok..So that means loosing IGP route will create an event driven BGP scan?
This command can be used to disable event based BGP scan.
R2(config)#router bgp 200
R2(config-router)#no bgp nexthop trigger enable
R2(config-router)#
The BGP scanner is legacy. Newer platforms use event-driven next-hop tracking as opposed to the scan time, which was used to poll the table every X interval. This tracking is on by default in any version that supports it.
http://www.cisco.com/c/en/us/td/docs/ios/12_2sb/feature/guide/sbbnhop.html