Issue

DHCP relay does not work with cl-mgmtvrf when the host and server facing ports are in the data plane.

Environment

Cumulus Linux 2.5.4 or 2.5.5
cl-mgmtvrf package versions earlier than 0.5
isc-dhcp-relay package versions earlier than 4.2.2.dfsg.1-5+deb70u6+cl2+3
DHCP relaying from one dataplane interface to another dataplane interface.

Resolution

Software Upgrade

Upgrade to Cumulus Linux 2.5.6 with cl-mgmtvrf=0.5 and isc-dhcp-relay=4.2.2.dfsg.1-5+deb70u6+cl2+3 or later. For more information, see RN-370.

Configuration Work Around

For switches running CL 2.5.4 or CL 2.5.5.

On the switch running dhcprelay, add an IP rule for the DHCP server address. Replace SERVER_IP with the SERVERS= value specified in /etc/default/isc-dhcp-relay/:

cumulus@switch$ sudo ip rule add from all to SERVER_IP lookup main

This rule can be applied at boot time, by specifying it in an up rule on the corresponding interface. The example below applies the SERVER_IP 172.16.0.1 to interface swp52:

auto swp52
iface swp52
    address 172.16.0.2/24
    up ip rule add from all to 172.16.0.1 lookup main

Diagnostic Steps

Run tcpdump from the switch on the host and server facing ports to trace traffic.

Stop the dhcprelay service.

cumulus@switch:~$ sudo service isc-dhcp-relay stop

Run the dhcprelay service in the foreground on the console to watch the output while issuing requests. The output below is an example of a successful session:

cumulus@switch:~$ sudo /usr/sbin/dhcrelay -d -i swp51 -i swp52 172.16.0.1
    Internet Systems Consortium DHCP Relay Agent 4.2.2
    Copyright 2004-2011 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/
Listening on LPF/swp2/44:38:39:00:25:d9
Sending on LPF/swp2/44:38:39:00:25:d9
Listening on LPF/swp1/44:38:39:00:25:d8
Sending on LPF/swp1/44:38:39:00:25:d8
Sending on Socket/fallback
Forwarded BOOTREQUEST for 68:05:ca:2f:7c:b3 to 172.16.0.1
Forwarded BOOTREPLY for 68:05:ca:2f:7c:b3 to 172.16.1.128
Forwarded BOOTREPLY for 68:05:ca:2f:7c:b3 to 172.16.1.128
Forwarded BOOTREQUEST for 68:05:ca:2f:7c:b3 to 172.16.0.1
Forwarded BOOTREPLY for 68:05:ca:2f:7c:b3 to 172.16.1.128
Forwarded BOOTREPLY for 68:05:ca:2f:7c:b3 to 172.16.1.128

dhcprelay requires additional IP rule with cl-mgmtvrf