Saturday, September 21, 2019

I’m questioning what I thought I knew about dhcp-relay

My understanding is that in dhcp-relay, the router will process the broadcast discover message, and generate a unicast packet and send one to each relay agent configured.

The servers will likely all reply with offers, which the router will forward on to the client, but the client will only respond with a request to the first server it receives the offer from, and ignore every other offer it gets back.

As a result when there’s multiple dhcp relay agents, it’s the one with the lowest latency to the respective client that typically becomes the client’s dhcp server moving forward.

So how is it after introducing a new dhcp relay agent to the config, do the clients on the subnet now show an almost perfect 50/50 split of which server is their dhcp server, when the A server is local at the site, and the B server is over 50ms of latency away?

My assumption was that the A server which is less than a millisecond away would win out for the vast majority of clients.



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