Customer has a simple ISIS adjacency between 2x devices and the ISIS is supplied with a BFD configuration.
If/when they disable ISIS on one of the devices - the BFD on remote end is clearly reporting the BFD session is down, however the ISIS adjacency ramains UP and it is going down only after Hold Timer.
The expectation is that BFD down should trigger the ISIS adjacency down.
labroot@jtac-acx7100-48l-ao-r2016# deactivate protocols isis
Mar 23 10:36:40
[edit]
labroot@jtac-acx7100-48l-ao-r2016# commit
Mar 23 10:36:42
commit complete
BFD Status at Peer:
---(refreshed at 2025-03-23 10:36:43 IST)---
Detect Transmit
Address State Interface Time Interval Multiplier
192.168.1.1 Up ae0.0 1.000 0.500 2
1 sessions, 1 clients
Cumulative transmit rate 2.0 pps, cumulative receive rate 2.0 pps
---(refreshed at 2025-03-23 10:36:44 IST)---
192.168.1.1 Down ae0.0 2.000 2.000 2
ISIS status at Peer
Interface System L State Hold (secs) SNPA
ae0.0 jtac-acx7100-48l-ao-r2016 2 Up 23
ae0.0 jtac-acx7100-48l-ao-r2016 2 Up 22
|
---(refreshed at 2025-03-23 10:37:06 IST)---
ae0.0 jtac-acx7100-48l-ao-r2016 2 Up 0
---(refreshed at 2025-03-23 10:37:08 IST)---
ae0.0 jtac-acx7100-48l-ao-r2016 2 Down 0
When we remove the ISIS/BFD config from one side, BFD session goes down due to "ADMIN DOWN" and in that case, it does not trigger ISIS adjacency down on PEER.
If BFD goes down due to any reason other than ADMIN DOWN, it informs IGP or whichever is the client of BFD to take action, like in case of ISIS, its like BFD tells ISIS to go down.
But in case of ADMIN DOWN, client does not take any action and it stays up, unless client's own keepalives are lost & client does not take any action on the BFD ADMIN DOWN message. This is a day 1 behavior.
If BFD will actually go down due to missing keepalives, It will go down due to Ctrl timer expiry and in that case ISIS will take action (like its adjacency will go down).