DHCP relay not working in CL 3.7

  • 6 June 2019
  • 1 reply

I have VXLAN EVPN fabric with asymetric routing, and when I try to setup DHCP relay it dont work:
net add dhcp relay server
net add dhcp relay interface swp49-52,vlan101-102
swp49-52 - uplinks.
Hosts - servers with subinterfaces(vlan 101 and 102) on bonding.
In vlan101 I have dhcp server, on subinterfaces in vlan102 I try to obtain DHCP but dhcrelay not seen any packets from servers.
In syslog I have no entryes about it.
when I try catch dhcp packets in tcpdump - on servers I can dump packets from all servers in 102 vni, even packets from servers behind other leafs. But whan I try dump dhcp pachets directly on switch - I dont see any dhcp packets neither on swp, neither on bonding, neither on SVI interfaces.

1 reply

Userlevel 5
DHCP relay in Vxlan environments can get tricky. I don't see too many asymmetric routing setups these days to know instantly what you're trying to do but regardless of Asymmetric versus Symmetric, the thing to keep in mind is that you need to have DHCP-relay applied on whatever machines have gateways for your VLAN and in the case of Asymmetric routing that means you may need to listen not just to local switchports, but to the VNI which handles your vlans as well to handle other devices elsewhere in the fabric which may not have access to the gateway on their leaf switches.