[FROG] /31s, scope link and FRR BGP

[Chris Malton (Delta V)]

Hi all,

I have /31s from an upstream provider on v4. If I specify "scope link" 
in /etc/network/interfaces for these, FRR seemingly doesn't allow the 
address to be used for update-source.

Minimal reproduction example (taken from one of my core routers):

/e/n/i config:

auto lo
iface lo inet loopback
	up ip addr add 195.246.200.2/32 scope global dev lo

auto ens4
iface ens4 inet static
	address 192.168.1.3/31
	scope link

FRR config:

router bgp 65000
  neighbor 192.168.1.2 remote-as 65001
  neighbor 192.168.1.2 interface ens4
  neighbor 192.168.1.2 update-source 192.168.1.3

What happens in this case, is that FRR sends updates from 172.16.0.2 
instead of 192.168.1.3 (despite being explicitly told otherwise!).

Have I found a bug, or have I done something stupid?

Thanks in advance.

Regards,

Chris Malton

-- 
Delta V Technologies Limited
03333 402 406    www.deltav-tech.co.uk
Office: 17 Elm Close, Southampton, SO16 7DT
Company No. 11006104 Registered in England and Wales