Hi Alistair,
If the default route on the switch is set to a next hop that is being provided by DHCP (default for the mgmt0 interface), the solution would be to disable DHCP, configure a static IP address on the mgmt interface, and then configure a new static default route with the next-hop IP of the gateway/firewall. Consider the following changes (which will need to be run from the serial console port or you will lose connectivity):
(config) # no interface mgmt0 DHCP
(config) # interface mgmt0 ip address x.x.x.x /x
(config) # ip default-gateway 0.0.0.0 0.0.0.0 10.10.55.10 <---------points to a gateway IP address off of VLAN 55 as seen down below
After making the above changes, the route table should reflect the new default route going out the VLAN interface.:
(config) # show ip route
Flags:
F: Failed to install in H/W
B: BFD protected (static route)
i: BFD session initializing (static route)
x: protecting BFD session failed (static route)
c: consistent hashing
p: partial programming in H/W
VRF Name default:
192.168.0.0 255.255.255.0 0.0.0.0 mgmt0 direct 0/0
default 0.0.0.0 10.130.55.10 vlan55 static 1/1
10.10.55.0 255.255.255.0 0.0.0.0 vlan55 direct 0/0
10.10.56.0 255.255.255.0 0.0.0.0 vlan56 direct 0/0
Please note: The next-hop address must be within the range of one of the IP interfaces on the system. In the example above, the vlan55 interface IP is 10.130.55.1. The gateway IP is on the same subnet as the VLAN interface.
Just for clarification, the mgmt0 interface needs to be on the same subnet as the MLAG VIP. The IPL addresses of the switches are on their own subnet. Please see the following link for more information:
https://community.mellanox.com/s/article/how-to-configure-mlag-on-mellanox-switches
Thanks,
Kevin