Hi, I'm trying to setup BFD multihop session between Bird 1.6.3 and a Juniper MX router to fast failover eBGP multihop sessions. I tried different configuration with no success, the current one is: ------------------------ protocol bfd { interface "*" { interval 300 ms; multiplier 3; }; multihop { interval 300 ms; multiplier 3; }; } protocol bgp { import none; multihop 2; export filter vips_filter; local 208.80.153.77 as 64605; neighbor 208.80.153.192 as 14907; bfd yes; } ------------------------ And the Juniper side: ------------------------ type external; multihop { ttl 2; } local-address 208.80.153.192; import anycast_import; family inet { unicast { prefix-limit { maximum 50; teardown; } } } export NONE; peer-as 64605; bfd-liveness-detection { minimum-interval 300; } multipath; neighbor 208.80.153.77; ------------------------ The firewalls on both sides allow udp/4784 udp/3784 udp/3785 to/from each side. The Bird's BFD state stays on Init, while Junos on Down. ------------------------ bird> show bfd sessions bfd1: IP address Interface State Since Interval Timeout 208.80.153.192 --- Init 15:47:25 2.000 6.000 ------------------------ cr1-codfw> show bfd session address 208.80.153.77 extensive Detect Transmit Address State Interface Time Interval Multiplier 208.80.153.77 Down 0.000 1.000 3 Client BGP, TX interval 0.300, RX interval 0.300 Local diagnostic None, remote diagnostic None Remote state AdminDown, version 1 Replicated Session type: Multi hop BFD Min async interval 0.300, min slow interval 1.000 Adaptive async TX interval 2.000, RX interval 2.000 Local min TX interval 2.000, minimum RX interval 0.300, multiplier 3 Remote min TX interval 0.000, min RX interval 0.000, multiplier 0 Local discriminator 3556, remote discriminator 0 Echo mode disabled/inactive, no-absorb, no-refresh Multi-hop min-recv-TTL 254, route table 0, local-address 208.80.153.192 Session ID: 0x4d954 1 sessions, 1 clients Cumulative transmit rate 1.0 pps, cumulative receive rate 0.0 pps ------------------------ We can see that Bird does send and receive BFD control packets, from/to the proper IPs. ------------------------ dns2001:~$ sudo tcpdump -p -i eno1 "host 208.80.153.192" 16:11:23.585910 IP cr1-codfw.wikimedia.org.49152 > dns2001.wikimedia.org.4784: UDP, length 24 16:11:23.643194 IP dns2001.wikimedia.org.35807 > cr1-codfw.wikimedia.org.4784: UDP, length 24 ------------------------ dns2001:~$ tailf /tmp/bird-debug.log 2018-11-20 15:49:20 <TRACE> bfd1: Sending CTL to 208.80.153.192 [Init] 2018-11-20 15:49:20 <TRACE> bfd1: CTL received from 208.80.153.192 [Down C] ------------------------ Running "monitor traffic" on the proper Junos interface doesn't show any BFD, but I believe that's because it's offloaded to the hardware (not seen on the routing engine). BGP on the other hand is properly established, so it's not a routing issue. I have some more troubleshooting in our ticket https://phabricator.wikimedia.org/T209989 Any pointers on miss-configurations, items to verify or other troubleshooting commands are welcome. Thank you. -- Arzhel