C613-50100-01 REV C Command Reference for x930 Series 2715
AlliedWare Plus™ Operating System - Version 5.4.6-1.x
DYNAMIC HOST CONFIGURATION PROTOCOL (DHCP) COMMANDS
IP
DHCP-RELAY MAX-MESSAGE-LENGTH
ip dhcp-relay max-message-length
Overview This command applies when the device is acting as a DHCP Relay Agent and DHCP
Relay Agent Option 82 insertion is enabled. It sets the maximum DHCP message
length (in bytes) for the DHCP packet with its DHCP Relay Agent Option 82 data
inserted. From this value it calculates the maximum packet size that it will accept
at its input. Packets that arrive greater than this value will be dropped.
The no variant of this command sets the maximum message length to its default
of 1400 bytes.
For DHCP Relay Agent and DHCP Relay Agent Option 82 introductory information,
see the DHCP Feature Overview and Configuration Guide.
Syntax
ip dhcp-relay max-message-length <548-1472>
no ip dhcp-relay max-message-length
Default The default is 1400 bytes.
Mode Interface Configuration for a VLAN interface.
Usage When a DHCP Relay Agent (that has DHCP Relay Agent Option 82 insertion
enabled) receives a request packet from a DHCP client, it will append the DHCP
Relay Agent Option 82 component data, and forward the packet to the DHCP
server. The DHCP client will sometimes issue packets containing pad option fields
that can be overwritten with Option 82 data.
Where there are insufficient pad option fields to contain all the DHCP Relay Agent
Option 82 data, the DHCP Relay Agent will increase the packet size to
accommodate the DHCP Relay Agent Option 82 data. If the new (increased) packet
size exceeds that defined by the maximum-message-length parameter, then the
DHCP Relay Agent will drop the packet.
NOTE: Before setting this command, you must first run the ip dhcp-relay agent-option
command. This will allow the DHCP Relay Agent Option 82 fields to be appended.
Example To set the maximum DHCP message length to 1200 bytes for packets arriving in
interface vlan7, use the commands:
awplus# configure terminal
awplus(config)# interface vlan7
awplus(config-if)# ip dhcp-relay max-message-length 1200
Parameter Description
<548-1472> The maximum DHCP message length (this is the message
header plus the inserted DHCP option fields in bytes).
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