IP Helper-Address For DHCP and WDS in Different VLANs

[chrismo16]

Scenario:

Clients on VLAN X

DHCP server on VLAN Y

WDS server on VLAN Z

We have IP helper-address command on our layer 3 device for DHCP. I would like to avoid using DHCP options and instead add another IP helper-address command to point clients to WDS as well. Is this possible? I know having two IP helper-address commands will direct traffic to both IPs but will this work correctly if the WDS server is not also hosting DHCP services?

[Richard Burts · Accepted solution]

It should work ok if WDS is not on the same machine as DHCP. My understanding is that Windows Deployment Service uses UDP ports 67, 69, and 4011. Normal helper address configuration should handle ports 67 and 69. To get helper address to forward port 4011 you would need to configure ip forward protocol for that port. As you mention using two helper addresses will result in copies of the broadcast packets being forwarded to both servers. So your DHCP server will receive some WDS packets (which it would ignore) and your WDS would receive DHCP packets (which it would ignore). So both functions should work.

HTH

Rick

[chrismo16]

Thanks for the reply Rick. I've read that port 4011 is only used when the WDS and DHCP roles are on the same machine and "do not listen on port 67" is checked. I'm currently building a testing environment to test your suggestion since doing so on the production network at work is frowned upon. 

[Richard Burts]

If WDS sometimes would use port 4011 then I would think it was prudent to configure support for that port. If you think it would not be used then you are certainly ok to not configure the forward protocol for that port. Configure it in your test environment and test. If it works that is great. If there are issues then you can add the forward protocol and see if it helps.

HTH

Rick

[chrismo16]

Thank you for the help Rick. Everything went well in the testing environment. Now it's time to sell our telecom department on the changes.

[Richard Burts]

Thanks for confirming that it did work in your test environment. I am confident that it will work in production as well. Thank you for using the rating system to mark this question as answered. This will help other readers in the forum to identify threads that have helpful information.

HTH

Rick