Configuring DHCP Relays

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Issue

How do I configure an interface so it can make DHCP relay requests for IPv4 and IPv6?

Environment

  • Cumulus Linux 1.5.z - 2.5.z

Note: For Cumulus Linux and Cumulus RMP 3.0 and later, please read the Cumulus Linux and Cumulus RMP user guides. 

Resolution

  1. Edit /etc/default/isc-dhcp-relay.
  2. Set SERVERS equal to the address of the DHCP server(s), in quotes and separated by spaces. For example:

    SERVERS="192.168.123.4"
    
  3. On the INTERFACES line, add both the client-facing and server-facing interfaces for the relay within the quotes, separated by spaces. For example, the client facing port is br0 and the server facing port is swp4.

    INTERFACES="br0 swp4"

    If you have multiple paths to the DHCP server or asymmetric routing, include all the incoming ports from which the DHCP response from the server may be received. Also, include the incoming port that receives the initial DHCP request from the host. For example, the host default gateway is br0, and swp4 and swp5 are equal cost paths to the DHCP server. Thus, a DHCP response may be received on swp4 or swp5.

    INTERFACES="br0 swp4 swp5"

    If using VLAN-aware bridges, apply addresses to Switch Virtual Interfaces for vlans that need relaying and specify the SVI bridge.tag interfaces in INTERFACES.

  4. Restart the DHCP relay service using init.d. The isc-dhcp-relay service points to /etc/default/isc-dhcp-relay as the default configuration file.
  5. cumulus@switch:~$ sudo /etc/init.d/isc-dhcp-relay restart

 

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