Building network automation solutions

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DHCP Relaying Details

Chinar Trivedi asked an interesting question about DHCP relaying in VXLAN/EVPN world on Twitter and my first thought was “that shouldn’t be hard” but when I read the first answer that turned into “wait a minute, how exactly does DHCP relaying works?

I’m positive there’s a tutorial out there somewhere, but I decided to go back to the sources of wisdom: the RFCs. It turned out to be a long walk down the IETF history lane.

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Test VRF-Aware DHCP Relaying with netlab

After figuring out how DHCP relaying works and testing it in a simple lab, I went a step further and tested VRF-aware DHCP relaying.

Lab Topology

I had to make just a few changes to the DHCP relaying lab topology:

  • DHCP server is running on CSR 1000v. IOSv DHCP server does not support subnet selection DHCP option and thus doesn’t work with relays that do inter-VRF DHCP relaying.
  • I put the link between the DHCP client and DHCP relay into a VRF.
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