DHCP-relay not working as expected with asymmetric routing

lodpp

Hi,

I'm hitting a weird behaviour with DHCP-relay with an assymetric routing case.

design.drawio.png

Hopefully the image will be explicit enough on the setup I'm using.

Context:

At the moment, SRV1 is single attached to pf2, pf2 is CARP MASTER.

PF2 (and PF1) are setup to do DHCP relay on its LAN interfaces and pointing to the dhcp server 192.168.0.42.

My LXC host is attached to a switch, dual attached to both PF1/2 with CARP.
CARP is MASTER on PF1 in this case

The LXC host has an internal bridge (without NAT) for the LXC guests. The LXC host act as default-gateway for the guests.

DHCP server is linux based with Kea running.

A static route exists on both PF1/PF2 to reach 192.168.0.0/24 via the LXC host.

OSPF/BGP routing setup exists between both PF1/PF2, so PF1 knows how to reach PF2 LAN networks ( and vice versa)

The problem:
In this particular case, when the SRV1 does a DHCP Discover, it never receives the DHCP Offer from the server.

SRV1 sends DHCP Discover via PF2
PF2 relays the DHCP Discover to the DHCP server
DHCP server gets the Discover and send the DHCP Offer via LXC-host
LXC-host routes the Offer to PF1
PF1 routes the Offer to PF2
PF2 receives the offer ( at least on the TCPdump, the offer hits the PF2:lanB interface.
PF2 does not send the offer to SRV1

Hotfix:
get all the CARP MASTER on the same box.

Tshoot:

Does anyone has a clue on what could be the problem ?

Thanks and best regards,
Nico