If you set these values it seems that iBGP sessions never fall over, however eBGP do due to fast external fall over enabled by default.
Although the bgp peering doesn't drop - there are no best paths.
I am using INE topology on R1 with interfaces s0/0 and s0/1 shutdown -
This is the state of the neighbors -
Rack15R1#show bgp ipv4 unicast summary | b Nei
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
155.15.13.3 4 200 1388 1384 0 0 0 00:10:54 Idle
155.15.146.4 4 100 3185 3193 96 0 0 00:20:43 14
155.15.146.6 4 100 588 591 96 0 0 00:20:45 11
And if you look at the peering to R4 and R6 you have -
Rack15R1#show bgp ipv4 unicast neighbors 155.15.146.4 | i keep
Last read 00:22:02, last write 00:03:30, hold time is 0, keepalive interval is 0 seconds
Configured hold time is 0, keepalive interval is 0 seconds
Rack15R1#show bgp ipv4 unicast neighbors 155.15.146.6 | i keep
Last read 00:06:16, last write 00:04:10, hold time is 0, keepalive interval is 0 seconds
Configured hold time is 0, keepalive interval is 0 seconds
My configuration is -
router bgp 100
template peer-policy RR
route-reflector-client
exit-peer-policy
!
template peer-session IBGP
remote-as 100
description IBGP peers
inherit peer-session TIMERS
exit-peer-session
!
template peer-session TIMERS
timers 0 0
exit-peer-session
!
no synchronization
bgp log-neighbor-changes
network 150.15.1.0 mask 255.255.255.0
neighbor 155.15.13.3 remote-as 200
neighbor 155.15.13.3 inherit peer-session TIMERS
neighbor 155.15.146.4 inherit peer-session IBGP
neighbor 155.15.146.4 inherit peer-policy RR
neighbor 155.15.146.6 inherit peer-session IBGP
neighbor 155.15.146.6 inherit peer-policy RR
no auto-summary
When interface f0/0 is shutdown we get the following -
*Jun 23 23:07:13.196: BGP(0): no valid path for 28.119.16.0/24
*Jun 23 23:07:13.196: BGP(0): no valid path for 28.119.17.0/24
*Jun 23 23:07:13.196: BGP(0): no valid path for 112.0.0.0/8
*Jun 23 23:07:13.196: BGP(0): no valid path for 113.0.0.0/8
*Jun 23 23:07:13.196: BGP(0): no valid path for 114.0.0.0/8
*Jun 23 23:07:13.196: BGP(0): no valid path for 115.0.0.0/8
*Jun 23 23:07:13.196: BGP(0): no valid path for 116.0.0.0/8
*Jun 23 23:07:13.196: BGP(0): no valid path for 117.0.0.0/8
*Jun 23 23:07:13.196: BGP(0): no valid path for 118.0.0.0/8
*Jun 23 23:07:13.196: BGP(0): no valid path for 119.0.0.0/8
*Jun 23 23:07:13.196: BGP(0): no valid path for 155.15.0.0/16
Rack15R1#
*Jun 23 23:07:13.196: BGP(0): no valid path for 205.90.31.0/24
*Jun 23 23:07:13.196: BGP(0): no valid path for 220.20.3.0/24
*Jun 23 23:07:13.196: BGP(0): no valid path for 222.22.2.0/24
And the bgp table looks like -
Rack15R1#show bgp ipv4 unicast
BGP table version is 96, local router ID is 150.15.1.1
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
* i28.119.16.0/24 204.12.15.254 0 100 0 54 i
* i 54.15.1.254 0 100 0 54 i
* i28.119.17.0/24 204.12.15.254 0 100 0 54 i
* i 54.15.1.254 0 100 0 54 i
* i112.0.0.0 204.12.15.254 0 100 0 54 50 60 i
* i 54.15.1.254 0 100 0 54 50 60 i
* i113.0.0.0 204.12.15.254 0 100 0 54 50 60 i
* i 54.15.1.254 0 100 0 54 50 60 i
* i114.0.0.0 204.12.15.254 0 100 0 54 i
* i 54.15.1.254 0 100 0 54 i
* i115.0.0.0 204.12.15.254 0 100 0 54 i
* i 54.15.1.254 0 100 0 54 i
* i116.0.0.0 204.12.15.254 0 100 0 54 i
* i 54.15.1.254 0 100 0 54 i
* i117.0.0.0 204.12.15.254 0 100 0 54 i
* i 54.15.1.254 0 100 0 54 i
* i118.0.0.0 204.12.15.254 0 100 0 54 i
Network Next Hop Metric LocPrf Weight Path
* i 54.15.1.254 0 100 0 54 i
* i119.0.0.0 204.12.15.254 0 100 0 54 i
* i 54.15.1.254 0 100 0 54 i
* i155.15.0.0 155.15.146.4 0 100 0 i
* i 155.15.146.6 0 100 0 i
* i205.90.31.0 155.15.45.5 0 100 0 200 254 ?
* i220.20.3.0 155.15.45.5 0 100 0 200 254 ?
* i222.22.2.0 155.15.45.5 0 100 0 200 254 ?
So I guess my question is why would you want to use these timer values? Clearly BGP won't install these paths - but the session remains up even though there is no connectivity to the peers -
Rack15R1#show ip cef 155.15.146.4 detail
0.0.0.0/0, epoch 0, flags default route handler
no route
Rack15R1#show ip cef 155.15.146.6 detail
0.0.0.0/0, epoch 0, flags default route handler
no route