BFD session down does not trigger BGP session down

[HareshKhandelwal]

Hi,

I observed this issue in my environment and wondering if this is expected.

computebgp-0# show ip bgp neighbors
BGP neighbor on eno2: fe80::e643:4bff:fe4a:c22, remote AS 64999, local AS 64999, internal link
Hostname: rhos-nfv-07.lab.eng.rdu2.redhat.com
Member of peer-group uplink for session parameters
BGP version 4, remote router ID 9.9.9.13, local router ID 192.168.80.115
BGP state = Established, up for 00:09:17 <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<NOTE THIS
Last read 00:00:17, Last write 00:00:17
Hold time is 180, keepalive interval is 60 seconds
Configured conditional advertisements interval is 60 seconds
Neighbor capabilities:
4 Byte AS: advertised and received
Extended Message: advertised and received
AddPath:
IPv4 Unicast: RX advertised and received
IPv6 Unicast: RX advertised and received
Extended nexthop: advertised and received
Address families by peer:
IPv4 Unicast
Long-lived Graceful Restart: advertised and received
Address families by peer:
Route refresh: advertised and received(old & new)
Enhanced Route Refresh: advertised and received
Address Family IPv4 Unicast: advertised and received
Address Family IPv6 Unicast: advertised and received
Hostname Capability: advertised (name: computebgp-0,domain name: n/a) received (name: rhos-nfv-07.lab.eng.rdu2.redhat.com,domain name: n/a)
Graceful Restart Capability: advertised and received
Remote Restart timer is 120 seconds
Address families by peer:
none
Graceful restart information:
End-of-RIB send: IPv4 Unicast, IPv6 Unicast
End-of-RIB received: IPv4 Unicast, IPv6 Unicast
Local GR Mode: Helper*
Remote GR Mode: Helper
R bit: False
N bit: False
Timers:
Configured Restart Time(sec): 120
Received Restart Time(sec): 120
IPv4 Unicast:
F bit: False
End-of-RIB sent: Yes
End-of-RIB sent after update: Yes
End-of-RIB received: Yes
Timers:
Configured Stale Path Time(sec): 360
IPv6 Unicast:
F bit: False
End-of-RIB sent: Yes
End-of-RIB sent after update: Yes
End-of-RIB received: Yes
Timers:
Configured Stale Path Time(sec): 360
Message statistics:
Inq depth is 0
Outq depth is 0
Sent Rcvd
Opens: 158 52
Notifications: 45 16
Updates: 181 166
Keepalives: 47545 47545
Route Refresh: 0 0
Capability: 0 0
Total: 47929 47779
Minimum time between advertisement runs is 0 seconds

For address family: IPv4 Unicast
uplink peer-group member
Update group 67, subgroup 67
Packet Queue length 0
Community attribute sent to this neighbor(all)
Outbound path policy configured
Outgoing update prefix filter list is *only-host-prefixes
0 accepted prefixes

For address family: IPv6 Unicast
uplink peer-group member
Update group 68, subgroup 68
Packet Queue length 0
Community attribute sent to this neighbor(all)
Outbound path policy configured
Outgoing update prefix filter list is *only-host-prefixes
0 accepted prefixes

Connections established 34; dropped 33
Last reset 00:09:19, No AFI/SAFI activated for peer
Message received that caused BGP to send a NOTIFICATION:
FFFFFFFF FFFFFFFF FFFFFFFF FFFFFFFF
00850104 FDE700B4 C0A85081 68020601
04000100 01020805 06000100 01000202
06010400 02000102 02800002 02020002
02460002 06410400 00FDE702 02060002
0A450800 01010100 02010102 10490E0C
636F6E74 726F6C6C 65722D30 00020440
02007802 10470E00 01018000 00000002
01800000 00
Internal BGP neighbor may be up to 1 hops away.
Local host: fe80::b533:41e0:a0b9:b7ba, Local port: 179
Foreign host: fe80::e643:4bff:fe4a:c22, Foreign port: 38124
Nexthop: 192.168.80.115
Nexthop global: fe80::b533:41e0:a0b9:b7ba
Nexthop local: fe80::b533:41e0:a0b9:b7ba
BGP connection: shared network
BGP Connect Retry Timer in Seconds: 120
Estimated round trip time: 2 ms
Read thread: on Write thread: on FD used: 29

BFD: Type: single hop
Detect Multiplier: 3, Min Rx interval: 300, Min Tx interval: 300
Status: Down, Last update: 0:00:09:19 <<<<<<<<<<<<<<<<<<<<<<<<<<NOTE THIS

computebgp-0# show bfd peers
BFD Peers:
peer fe80::e643:4bff:fe4a:c22 local-address fe80::b533:41e0:a0b9:b7ba vrf default interface eno2
ID: 1578519708
Remote ID: 0
Active mode
Status: down <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<NOTE THIS
Downtime: 0 second(s)
Diagnostics: control detection time expired
Remote diagnostics: control detection time expired
Peer Type: dynamic
Local timers:
Detect-multiplier: 3
Receive interval: 300ms
Transmission interval: 300ms
Echo receive interval: 50ms
Echo transmission interval: disabled
Remote timers:
Detect-multiplier: 3
Receive interval: 1000ms
Transmission interval: 1000ms
Echo receive interval: 50ms

My config is:
router bgp 64999
bgp router-id 192.168.80.115
bgp log-neighbor-changes
no bgp ebgp-requires-policy
no bgp suppress-duplicates
no bgp hard-administrative-reset
no bgp default ipv4-unicast
bgp graceful-shutdown
no bgp graceful-restart notification
no bgp network import-check
neighbor uplink peer-group
neighbor uplink remote-as internal
neighbor uplink bfd
neighbor uplink bfd profile tripleo
neighbor uplink ttl-security hops 1
neighbor eno2 interface peer-group uplink

My usecase here is very simple, unnumbered iBGP session between 2 peers connected via uplink switch in same vlan.
eno2 (physical interface) here is plain ethernet interface.

I brought down BFD purposefully here. However, bringing BFD up/down does not impact BGP session.

Can anyone confirm this behavior?

Thanks
-Haresh