Possibility of a dhcp-relay chain (DHCP server--Router1---Router2--DHCPClient) multiple routers dhcp relay

General questions
1

Hi there,

I am trying to figure out how to relay dhcp requests from a client to a dhcp server that are seperated by two vyos routers. Currently how it is set up is that router A and B are directly connected to each other, but client is behind router A and server is behind Router B. I assume that this requires some sort of relay-chain from router A to B but I am not sure which settings to apply for each router. I’ve tried various combinations of the relay-agents-packets on both routers but alas it did not make a different. If you have dealt with this before or might know a solution please let me know! Thank you.

  • S
2

You shouldn’t need a “relay-chain” you just setup DHCP relay on Router A so that it is relaying requests to the IP Address of the DHCP server behind B.
Config to apply to Router A:

# show service dhcp-relay
     interface eth1  <------- Interface on Router A that has your client(s) on it.
     server X.X.X.X <-------- IP Address of the DHCP Server attached to Router B.
     relay-options {
        relay-agents-packets discard
     }

As long as routing is working correctly between everything, this should be enough.

In other breaking news: Welcome to the Vyos Forums :slight_smile:

1 Like
3

Thanks for the solution you’ve posted. I’m currently dealing with a wan load balancing issue so I am not able to test the relay on the environment right now. I’ll keep you posted once that is working. Thank you for the warm welcome. Glad to be here! :slightly_smiling_face:

4

Just tested it with the right load balancing config and good news is that it works now, although I had to also enter the interface of router A that connected to router B in the dhcp-relay settings, so in this case both interfaces that played a part in routing the dhcp packets from client to server need to be declared via the set dhcp-relay interface command. Thanks again for your help!

1 Like
5

Most welcome, glad you got it working!

6

Yes your observation is correct the source and destination interfaces need to be added for dhcp relay as both are bidirectional, you can not specify originating/forwarding, you must specify all of them due to this.
You can see it via logs when you start up or restart dhcp-relay.

7

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