BFD session on Loopback interfaces

[kperumalbfn]

Hi,

Trying to bring up a BFD session between Loopback address configured on directly connected nodes.

NODE1(Loopback-10.1.0.32, BFD Active mode)<--->NODE2(Loopback 10.2.0.1, BFD Passive mode)

Both the Loopback addresses are reachable via static routes configured on both the nodes.

NODE1# show bfd peers
BFD Peers:
peer 10.2.0.1 local-address 10.1.0.32 vrf default
ID: 1532873704
Remote ID: 0
Active mode
Status: down

NODE1# show interface Loopback0
Interface Loopback0 is up, line protocol is up
inet 10.1.0.32/32 unnumbered

NODE2# show bfd peers
BFD Peers:
peer 10.1.0.32 local-address 10.2.0.1 vrf default
ID: 4130411947
Remote ID: 0
Passive mode
Status: down

NODE2# show interface Loopback0
Interface Loopback0 is up, line protocol is up
inet 10.2.0.1/32 unnumbered
inet6 fe80::2064:96ff:fe4f:564/64

FRRouting 8.5.1 on both the nodes

Tcpdump on NODE2 shows that BFD packets are received from NODE1, but BFDD is not receiving those packets. Zebra and BFD debugs didn't show any errors.

When I configure the BFD sessions using directly connected interface address, sessions are up. Problem seems to be with loopback address. If anyone have tried the same, please provide some details.

Thanks,

[pguibert6WIND]

I think only multihop should work, because your ttl is decremented twice

[kperumalbfn]

Thanks @pguibert6WIND

Same result with multihop option as well.

NODE1# show bfd peers
BFD Peers:
peer 10.2.0.1 multihop local-address 10.1.0.32 vrf default
ID: 654345389
Remote ID: 0
Active mode
Minimum TTL: 254

NODE1# show bfd peers counters
BFD Peers:
peer 10.2.0.1 multihop local-address 10.1.0.32 vrf default
Control packet input: 0 packets
Control packet output: 50 packets
Echo packet input: 0 packets

NODE2# show bfd peers
BFD Peers:
peer 10.1.0.32 multihop local-address 10.2.0.1 vrf default
ID: 800544439
Remote ID: 0
Passive mode
Minimum TTL: 254
Status: down

NODE2# show bfd peers counters
BFD Peers:
peer 10.1.0.32 multihop local-address 10.2.0.1 vrf default
Control packet input: 0 packets
Control packet output: 0 packets
Echo packet input: 0 packets
Echo packet output: 0 packets
Session up events: 0
Session down events: 0
Zebra notifications: 0

BFD peer counter dump shows that bfd is not receiving the packet('Control packet input' is zero).

[kperumalbfn]

BFD packets were dropped due to iptables rule set for loopback IPs. After updating iptable rules, BFD sessions are up between loopback IPs.