BFD protocol doesn't send packets after link flap up on switch

[Jakub Nowacki]

Hi,

I have multihop BGP peering with BFD setup on it. One of the peers is a
switch that runs Linux. I've run into situation where after link flap on
interface that switch connects to BFD protocol after successfully detecting
that flap BFD session cannot reestablich because switch side stops sending
BFD packets. I'm suspecting that this is due to switch behavior that
removes IP address of link when it goes down (BGP and BFD are using
interface ip address to connect). Bird is trying to bind to IP address that
is no longer available and that causes the issue.

Logs below show following events
1. Correct BFD packet exchange
2. Link flaps at 14:07:38
3. Link is back up, starts receiving BFD packets from peer and state
changes from Down to Init at 14:07:45. Note that no BFD packets are being
generated, where they should be.
4. Removing 'bfd;' line and reconfiguring at 14:08:31
5. Adding 'bfd; line and reconfiguring at 14:08:47 which successfully
restart BFD.

2018-08-24 14:07:37 <TRACE> bfd1: CTL received from 172.30.2.1 [Up A]
2018-08-24 14:07:37 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:07:38 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:07:38 <TRACE> bfd1: CTL received from 172.30.2.1 [Up A]
2018-08-24 14:07:38 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:07:38 <TRACE> bfd1: CTL received from 172.30.2.1 [Up A]
2018-08-24 14:07:38 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:07:38 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:07:38 <ERR> bfd1: Socket error: Invalid argument
2018-08-24 14:07:38 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:07:38 <ERR> bfd1: Socket error: Invalid argument
2018-08-24 14:07:38 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:07:38 <ERR> bfd1: Socket error: Invalid argument
2018-08-24 14:07:38 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:07:38 <ERR> bfd1: Socket error: Invalid argument
2018-08-24 14:07:38 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:07:38 <ERR> bfd1: Socket error: Invalid argument
2018-08-24 14:07:38 <TRACE> bfd1: Session to 172.30.2.1 expired
2018-08-24 14:07:38 <TRACE> bfd1: Session to 172.30.2.1 changed state from
Up to Down
2018-08-24 14:07:38 <TRACE> bgp_gw_rs_1: BFD session down
2018-08-24 14:07:38 <TRACE> bfd1: Session to 172.30.2.1 removed
2018-08-24 14:07:38 <ERR> bfd1: Socket error: bind: Cannot assign requested
address
2018-08-24 14:07:38 <TRACE> bfd1: Session to 172.30.2.1 added
2018-08-24 14:07:44 <TRACE> bfd1: CTL received from 172.30.2.1 [Down A]
2018-08-24 14:07:44 <TRACE> bfd1: Session to 172.30.2.1 changed state from
Down to Init
2018-08-24 14:07:45 <TRACE> bfd1: CTL received from 172.30.2.1 [Down A]
2018-08-24 14:07:46 <TRACE> bfd1: CTL received from 172.30.2.1 [Down A]
2018-08-24 14:07:46 <TRACE> bfd1: CTL received from 172.30.2.1 [Down A]
2018-08-24 14:07:47 <TRACE> bfd1: CTL received from 172.30.2.1 [Down A]
...
2018-08-24 14:08:30 <TRACE> bfd1: CTL received from 172.30.2.1 [Down A]
2018-08-24 14:08:31 <TRACE> bfd1: CTL received from 172.30.2.1 [Down A]
2018-08-24 14:08:31 <TRACE> bfd1: Session to 172.30.2.1 removed
2018-08-24 14:08:31 <TRACE> bfd1: Reconfigured
2018-08-24 14:08:47 <TRACE> bfd1: Session to 172.30.2.1 added
2018-08-24 14:08:47 <TRACE> bfd1: Session to 172.30.2.1 reconfigured
2018-08-24 14:08:47 <TRACE> bfd1: Reconfigured
2018-08-24 14:08:47 <TRACE> bfd1: CTL received from 172.30.2.1 [Down A]
2018-08-24 14:08:47 <TRACE> bfd1: Session to 172.30.2.1 changed state from
Down to Init
2018-08-24 14:08:47 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Init A]
2018-08-24 14:08:47 <TRACE> bfd1: CTL received from 172.30.2.1 [Up PA]
2018-08-24 14:08:47 <TRACE> bfd1: Session to 172.30.2.1 changed state from
Init to Up
2018-08-24 14:08:47 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up FA]
2018-08-24 14:08:47 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up PA]
2018-08-24 14:08:47 <TRACE> bfd1: CTL received from 172.30.2.1 [Up FA]
2018-08-24 14:08:47 <TRACE> bfd1: CTL received from 172.30.2.1 [Up A]
2018-08-24 14:08:47 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]
2018-08-24 14:08:47 <TRACE> bfd1: CTL received from 172.30.2.1 [Up A]
2018-08-24 14:08:47 <TRACE> bfd1: Sending CTL to 172.30.2.1 [Up A]


Kuba Nowacki
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