DHCP-relay in MPLS VRF

RouterOS Forwarding Protocols
1

Hi all!

I’m trying to setup a dhcp-relay which should relay requests through a L3 MPLS-VPN but can’t get it to work.
It seems like the relay request are sent via the main routing-table (default gw) and not the vrf.

I’ll try to illustrate:
[DHCP server (192.168.88.1)] --vrf1-- [PE1] —MPLS Cloud (main)— [PE2] --vrf1-- [DHCP Client]

PE2 has dhcp-relay setup: (ether1=main, ether2=vrf1)
/ip dhcp-relay add delay-threshold=none dhcp-server=192.168.88.1 disabled=no interface=ether2 local-address=192.168.92.2 name=relay1

When I sniff at PE2 on ether1 I see DHCP unicast IP-packet and not a MPLS-encapsulated packet.

Anyone got an idea about this? Limitation?

2

DHCP relay is not VRF aware, so it is not going to work.

3

Ok, thanks.

4

After some time considering this, any plans to implement?
Would be nice to have. :slight_smile:

5

Hey,

I have come across the same dilemma…

Trying to relay DHCP over a routed MPLS network, from a windows DHCP server, to clients on VRF’s across a WAN.

Is there any fix to this? Seems to work fine on Cisco hardware, just stumped on the Mikrotiks.

Cheers,

Andy

6

I was able to do a workaround with one mangle and one nat rule to make this work.
Make you sure you have a route for the DHCP server in the main table, default route is enough (or else the router will drop the packet) and create a mangle rule kind of like this:

ip firewall mangle add chain=output  dst-address=<dhcpserver> protocol=udp dst-port-67 action=mark-routing new-routing-mark=<vrf>

Possible you need a nat rule to make sure the source address is correct for the customers network:

 
ip firewall nat add chain=srcnat dst-address=<dhcpserver> protocol=udp dst-port=67 routing-mark=<vrf> action=src-nat to-addresses=<relayip>

relayip is the address you have assigned on the interface facing the customers network.

Hope this helps.

7

Thanks heaps norpan,
worked perfectly! Didn’t need the nat rule it seemed.

Now I can get things rolling! :smiley: