DHCP Relay Operational Commands

Verify DHCP Relay Configuration

A good starting point for any troubleshooting is to get an overview about the configuration.

First check the DHCP server configuration and optionally check the reachability using additional commands like ping.

supervisor@rtbrick>LEAF01: cfg> show config access dhcp-server
{
    "rtbrick-config:dhcp-server": [
      {
        "server-name": "server1",
        "address": "198.51.100.15",
        "source-address": "198.51.100.101",
        "routing-instance": "default"
      }
    ]
  }

In the next step it should be verified that the DHCP relay function is enabled for the desired logical interfaces. Those interfaces must be configured with a valid local or borrowed (unnumbered) IPv4 address.

supervisor@rtbrick>LEAF01: cfg> show config access dhcp-relay
{
    "rtbrick-config:dhcp-relay": [
      {
        "interface": "ifl-0/0/1/1",
        "dhcp-server": [
          "server1",
          "server2"
          ]
      }
    ]
  }

Verify DHCP Relay Packet Processing

All DHCP packets processed by RBFS will be handled by the IPoE daemon (rtbrick-ipoed.1) which separates between DHCP relay and subscriber packets.

The command show dhcp statistics gives some statistics about the DHCP packets send and received by the IPoE daemon.

supervisor@rtbrick>LEAF01: op> show dhcp statistics
Packets received            : 0
Decode error                : 0
Relay packets received      : 0
Relay packets sent          : 0
Relay send error            : 0
Subscriber packets received : 0
Subscriber packets sent     : 0
Subscriber send error       : 0

Received malformed packets will be counted here as part of the shared DHCP packet infrastructure.

Those statistics can be reset with the command clear dhcp statistics.

In the next step, the command show dhcp relay statistics provides more detailed statistics for those packets handled by the DHCP relay function.

supervisor@rtbrick>LEAF01: op> show dhcp relay statistics
Packet           Received         Sent
DHCP DISCOVER  : 0                0
DHCP OFFER     : 0                0
DHCP REQUEST   : 0                0
DHCP DECLINE   : 0                0
DHCP ACK       : 0                0
DHCP NAK       : 0                0
DHCP RELEASE   : 0                0
DHCP INFORM    : 0                0

Errors:

Invalid client packets received : 0
Invalid server packets received : 0
I/O errors                      : 0
Configuration errors            : 0

A DHCP packet is consider as invalid if correctly formed but some invalid or unexpected values like a DHCP hop count greater than 16, messages from server without server identifier option, non-matching transaction (XID) and many more.

Those statistics can be reset with the command clear dhcp relay statistics.

Verify DHCP Relay Bindings

The DHCP relay function tracks all active DHCP communications as so called bindings. The command show dhcp relay binding allows to verify those bindings with extensive filters to better navigate in scaled environments with thousands of bindings.

supervisor@rtbrick>LEAF01: op> show dhcp relay binding ?
  <cr>
  detail                Detailed binding information
  filter                Filter DHCP relay binding
  interface             Interface
supervisor@rtbrick>LEAF01: op> show dhcp relay binding filter ?
  address               Client IP address
  count                 Count matching bindings
  detail                Detailed binding information
  interface             Interface
  interface-regex       Interface regex
  mac                   Hardware address
  mac-regex             Hardware address regex
  server                Server identifier
supervisor@rtbrick>LEAF01: op> show dhcp relay binding detail
Interface                  : ifp-0/0/1/3
Hardware Address           : 02:00:00:00:00:01
Client IP Address          : 198.51.100.58
Routing Instance           : default
Proxy Mode                 : enabled
Server Identifier          : 198.51.100.15
Gateway IP Address         : 198.51.100.35
Lease Time                 : 120.0 sec
Lease Start                : Tue Nov 16 22:27:15 GMT +0000 2021
Lease Expires              : 66.0 sec
Last Packet Received       : Tue Nov 16 22:27:15 GMT +0000 2021
Last Received Packet Type  : ACK
Last Packet Sent           : Tue Nov 16 22:27:15 GMT +0000 2021
Last Sent Packet Type      : ACK

The most extensive output is provided by selecting a particular binding using the interface and client MAC address as key.

supervisor@rtbrick>LEAF01: op> show dhcp relay binding interface ifp-0/0/1/3 mac 02:00:00:00:00:01
Interface                  : ifp-0/0/1/3
Hardware Address           : 02:00:00:00:00:01
Client IP Address          : 198.51.100.58
Routing Instance           : default
Proxy Mode                 : enabled
Server Identifier          : 198.51.100.15
Gateway IP Address         : 198.51.100.35
Lease Time                 : 120.0 sec
Lease Start                : Tue Nov 16 22:31:15 GMT +0000 2021
Lease Expires              : 104.0 sec
Last Packet Received       : Tue Nov 16 22:31:15 GMT +0000 2021
Last Received Packet Type  : ACK
Last Packet Sent           : Tue Nov 16 22:31:15 GMT +0000 2021
Last Sent Packet Type      : ACK

Statistics:

Packet           Received         Sent
DHCP DISCOVER  : 1                1
DHCP OFFER     : 1                1
DHCP REQUEST   : 36               36
DHCP DECLINE   : 0                0
DHCP ACK       : 36               36
DHCP NAK       : 0                0
DHCP RELEASE   : 0                0
DHCP INFORM    : 0                0

Errors:

Invalid client packets received : 0
Invalid server packets received : 0
I/O errors                      : 0
Configuration errors            : 0

This output returns additional statistics per DHCP relay binding.

The command clear dhcp relay binding removes either all bindings, all bindings of a corresponding interface or only one particular binding.

supervisor@rtbrick>LEAF01: op> clear dhcp relay binding ?
  all                   Clear all DHCP relay bindings
  interface             Interface
supervisor@rtbrick>LEAF01: op> clear dhcp relay binding all
supervisor@rtbrick>LEAF01: op> clear dhcp relay binding interface ifp-0/0/1/3
supervisor@rtbrick>LEAF01: op> clear dhcp relay binding interface ifp-0/0/1/3 mac 02:00:00:00:00:01