General
If we are using Multi-hop BFD between N9K and Non-N9K device with update-source loopback on N9K and SVI on Non-N9K. N9K and Non-N9K are in different AS with ebgp neighborship inbetween. The BFD view on N9K is multi-hop but on non-N9K is single-hop. It means the device across the link will send BFD message with port number of the single hop.
In 'show bfd ipv6 neighbor', we can see the following output even we have ebgp-multihop 255 configured
OurAddr NeighAddr
LD/RD RH/RS Holdown(mult) State Int Vrf Type
fa00:1::1 fc00:1::2 1090519045/0 Down N/A(3) Down Vlan100 default SH
For connectivity wise,
Direct BGP is up
Multihop BGP is up
Ping6 is passing
BFD got ICMPV6 unreachable
BFD is at state admin down
TX is sending but RX counter remain 0
Session state is Down and not using echo function
Session type: Singlehop
Rx Count: 0, Rx Interval (ms) min/max/avg: 0/0/0 last: 743090 ms ago
Tx Count: 389, Tx Interval (ms) min/max/avg: 1893/1893/1893 last: 1479 ms ago
State bit: AdminDown - Demand bit: 0
Min Echo interval: 0 - Authentication bit: 0
Hosting LC: 1, Down reason: No Diagnostic, Reason not-hosted: None
Symptom
IPV6 Multi-hop BFD does not comes up between N9K and non-N9K devices under ebgp setup even the full connectivity is maintained.
Conditions
pesudo configuration
router bgp 1
neighbor
bfd
bfd multihop interval 250 min_rx 250 multiplier 3
remote-as 2
update-source loopback0
ebgp-multihop 255
address-family ipv6 unicast
vica versa on ASR
N9K is running 9.3.4 software release
Software
BIOS: version 05.40
NXOS: version 9.3(4)
Tested between N9K ASR directly connected. N9K side with following
