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Routing

DHCP-Relay not forwarding remote DHCP DISCOVER packets over EVPN/Virtual Switch

[ Edited ]
‎10-31-2018 04:31 AM

Both routers running 18.3R1.9

 

Topology:

Remote Laptop (DHCP Client)-->(Access Port) MX40 (PE-2)<--->EVPN/Virtual Switch<--->MX104 (PE-1 w/ IRB as DHCP Relay)-->DC w/ DHCP Server

 

We are migrating VPLS to EVPN/Virtual Switch and I found that at pure layer 2 CE to CE communications are fine. MAC learning is performed as expected between PEs using MBGP (family evpn). Now I need to support DHCP relay for remote clients using an IRB interface and when I monitor traffic at PE-1 on the IRB, I see the DHCP DISCOVER packets over an over, but the PE never forwards/relays the traffic to the DHCP server. I should note a locally connect DHCP client on PE-1 works fine and pulls an IP as expected.

 

So...the issue is relaying remotely sourced DHCP DISCOVER packets. Note that this worked fine using VPLS and an lt interface as the relay. I simply replaced the VPLS instance with a EVPN instance and replaced the lt interface with an IRB interface.

 

Oddly enough...I replaced the DHCP-Relay config with a bootp config and the problem is reversed! Remote clients can pull an IP but a locally attached client can not!

 

I prefer to use the dhcp-relay rather than bootp. 

 

See attached configs and monitor traffic output. MAC learning is perfect, but the PE-1 will not forward the DHCP DISCOVER traffic.

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