BFD on static route for secondary interface IP in IOS-XR (ASR9K)

[Anomitra]

I have a setup where I need to run BFD on a static route, given below.

R1 and R2 are ASR9K routers running IOS XR version 7.6.2

N1 and N2 are components of a device that act as an L3 switch. The configs are similar on these devices.

On R1, the bfd runs fine.

On R2, the static route is corresponding to the secondary IP of the interface. The bfd is down on this leg.

The config is given below.

On R2, show bfd session detail shows that the source IP is the primary interface IP.

I did not find any documentation related to running bfd on the secondary interface IP.

Any help would be appreciated.

R1#
interface Bundle-Ether1.100
ipv4 address 10.10.10.1 255.255.255.0
encapsulation dot1q 100

router static
address-family ipv4 unicast
30.30.30.0/24 Bundle-Ether1.100 10.10.10.2 bfd fast-detect minimum-interval 200 multiplier 3

R2#
interface Bundle-Ether1.200
ipv4 address 20.20.20.1 255.255.255.0
ipv4 address 100.100.100.1 255.255.255.0 secondary
encapsulation dot1q 200

router static
address-family ipv4 unicast
30.30.30.0/24 Bundle-Ether1.200 100.100.100.2 bfd fast-detect minimum-interval 200 multiplier 3
R2#show bfd session detail interface be1.200 destination 100.100.100.2
I/f: Bundle-Ether1.200, Location: 0/0/CPU0
Dest: 100.100.100.2
Src: 20.20.20.1
State: DOWN for 0d:0h:13m:35s, number of times UP: 0
Session type: SW/V4/SH/BL
-----------------------
-----------------------
-----------------------

[paul driver]

Hello
The rtr should send a BFD packet using its own sip/dip to send to its BFD neighbour, the BFD neighbour send this back to the rtr , then the rtr knows its neighbour is active, My understanding by default the primary interface is used, and not the secondary for this interaction

[Anomitra]

Hello Paul, thanks for your reply.

Does that mean bfd on a secondary IP is not supported? Or is there any configuration to make the router use the secondary IP?

[paul driver]

Hello
Just noticed this is in XR, so globally you should be able to set the source for BFD
example:
conf t
bfd
echo ipv4 source xxx

[Anomitra]

Hello Paul

won't this update the source IP for all bfd sessions?

even if I configure the echo source ip under the interface, it will update the source for the primary IP also, right?

I have a bfd running on the primary IP too, so that might get affected.

I realised I may be able to configure a loopback IP as the source in global mode, but that again would affect all bfd sessions.

I am working on a production router of a service provider, so won't be able to do that.

[Giuseppe Larosa]

Hello @Anomitra ,

on the affected router on the BVI swap primary and secondary IP address like the following:

interface Bundle-Ether1.200
ipv4 address 20.20.20.1 255.255.255.0 secondary
ipv4 address 100.100.100.1 255.255.255.0
encapsulation dot1q 200

You can do it only if you are not using the current primary address with routing protocol like OSPF.

Hope to help

Giuseppe

[Anomitra]

Hello Giuseppe, thanks for your reply, but no, I wont be able to do that.

There is a bfd running for the primary IP also.

[Giuseppe Larosa]

Hello @Anomitra ,

I would suggest you to give a look at BFD Multi hop ove BVI

https://www.cisco.com/c/en/us/td/docs/iosxr/ncs5500/routing/76x/b-routing-cg-ncs5500-76x/implementing-bfd.html#Cisco_Generic_Topic.dita_f2ca4563-26a8-41d8-92f7-780a3aad00d6

because the peer to be able to answer back has to send back to the primary address that is used as source

Hope to help

Giuseppe

[MHM Cisco World]

try below to config source per interface not globally

configure

bfd

interface type interface-path-id

echo ipv4 source ip-address

Use the commit or end command.

[Anomitra · Accepted solution]

Thanks for all the responses, they have been helpful.

Unfortunately, I won't be able implement any of them since they would affect the existing bfd sessions.

We have decided to change the design to use the existing primary IP for this link.

[MHM Cisco World]

believe me that better 
use secondary have many many limitation

MHM