Command Reference Guide

212 ● ip df-check enable 3Com Router 5000 Family and Router 6000 Family
Command Reference
ip df-check enable
Purpose Use the ip df-check enable command to enable don’t fragment bit (DF-bit)
check for IP packets.
Use the undo ip df-check enable command to disable DF-bit check for IP
packets.
Syntax ip df-check enable
undo ip df-check enable
Parameters None
Default By default, DF-bit check is enabled for IP packets.
Example Enable DF-bit check for IP packets.
[Router] ip df-check enable
View This command can be used in the following views:
■ System view
Description With DF-bit check enabled, the router checks the DF bit in the IP header. If an arriving
packet with the DF bit set to 1 is greater than the MTU of the outgoing interface, the
router does not fragment the packet; instead, it drops the packet and sends back an
ICMP message carrying the code of fragmentation needed and DF set.
Before disabling DF-bit check for IP packets, you must ensure that it is disabled on all
the devices along the link.