This article will provide information about how to use DHCP-Relay in MC-LAG setup.

When we configure DHCP-Relay in MC-LAG setup, it may not work as expected

• As per the below topology

• MC-LAG peers are acting as DHCP-Relay, the DHCP server is VM machine where its configured one port as active and other one as standby.
• The clients are getting the IP address from the DHCP server as expected from one of the MC-LAG peer; however from the MC-LAG peer, it's stuck in select and request state and there is no reachability from the concerned peer to DHCP server.
• Please check the configuration of MC-LAG and check whether you have enabled VRRP or mac-synchronize.
• As per MC-LAG best practise configuration we cannot configure both MAC synchronization and VRRP. 
• If the MC-LAG is configured with mac-synchronize then DHCP relay is not supported. If DHCP relay is required, configure VRRP over IRB or RVI for Layer 3 functionality.

https://www.juniper.net/documentation/us/en/software/junos/mc-lag/topics/concept/best-practices-usage-notes.html#best-practices-and-usage-notes__section_tqt_dsn_cxb

• Please enable VRRP for the IRB interface and initiate the DHCP packet from client and check the DHCP Relay binding using "show dhcp relay binding"
• Make sure the configuration is fine and you have reachability to server from both the MC-LAG peers.
• If you are still observing issue with DHCP-Relay, please open a JTAC case to check the issue further.