Catalyst9300 BGP peering with secondary IP and BFD

[mhiyoshi]

Hi all,

I think normally BFD session is 1 by 1 like below right?

interface Vlan100
ip address 10.1.1.1 255.255.255.252
bfd interval 100 min_rx 100 multiplier 5

However if I want to use secondary IP address is it possible to establish BFD session between secondary IPs?

interface Vlan100
ip address 10.1.1.1 255.255.255.252
ip address 20.1.1.1 255.255.255.252 secondary
bfd interval 100 min_rx 100 multiplier 5

I appreciate to let me know any related URL If there is any limitaion.

Best Regards,

Masanobu Hiyoshi

[balaji.bandi]

Can run BGP using the Loopback address right? what is the Limitation here:

I was not tested using a secondary IP address with BFD - BFD you need to consider some Limitations: 

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9300/software/release/17-3/configuration_guide/rtng/b_173_rtng_9300_cg/configuring_bidirectional_forwarding_detection.html

[mhiyoshi]

Hi, thank you for your information. I think there is a limitation on the BFD related URL below.

Restrictions for Bidirectional Forwarding Detection

BFD works only for directly connected neighbors.
BFD neighbors must be no more than one IP hop away. BFD does not support Multihop configurations.

Based on this, I have checked the configuration.Here is the output below.

This is iBGP example however eBGP also same result.

ip route 2.2.2.2 255.255.255.255 10.0.10.2
!
interface Loopback0
 ip address 1.1.1.1 255.255.255.255
 bfd interval 50 min_rx 50 multiplier 3
!
router bgp 100
 neighbor 2.2.2.2 remote-as 100
 neighbor 2.2.2.2 update-source Loopback0
 neighbor 2.2.2.2 fall-over bfd multi-hop 
*I've just tried this option however there is no BFD session.

R1#sh ip bgp summary
BGP router identifier 1.1.1.1, local AS number 100
BGP table version is 1, main routing table version 1

Neighbor        V           AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
2.2.2.2         4          100      10      10        1    0    0 00:05:40        0

R1#sh bfd neighbors
R1#

[Reza Sharifi]

Hi,

neighbor 2.2.2.2 update-source Loopback0

BFD only works when the devices (2) are directly connected. It does not work with loopbacks.

HTH

[mhiyoshi]

Hi, Reza,

Thank you for your information. Now I understand this limitation however if I want to use secondary IP address is it possible to establish BFD session between secondary IPs?

interface Vlan100
ip address 10.1.1.1 255.255.255.252
ip address 20.1.1.1 255.255.255.252 secondary
bfd interval 100 min_rx 100 multiplier 5

[rasmus.elmholt]

Hi @mhiyoshi 

Did you ever find a solution for this?

I have a setup as well, where we are running eBGP on the secondary address of a link, and I cannot get BFD up.