Icmp Redirect; Important Considerations - 3Com corebuilder 3500 Implementation Manual

292 C 11: I
HAPTER NTERNET

ICMP Redirect

Important
Considerations
P (IP)
ROTOCOL
ICMP Redirect adds another layer of intelligence to routing. ICMP
Redirect:
Informs the sending device of the frame that there is a more efficient
route to the destination.
Routes the frame via the more efficient route.
Use the Administration Console or the Web Management software to
enable ICMP Redirect.
Keep the following things in mind with ICMP Redirect:
ICMP Redirect determines if the sending interface is the same as the
receiving interface.
ICMP Redirect determines if the source device of the frame is on a
direct-connect network. See Figure 57.
You can enable or disable ICMP Redirect on a per-interface basis.
There is a performance cost associated with this redirect activity. You
have to monitor the activity to gauge its effect on the network.
Performance can be affected if the sending device ignores the
recommendations of ICMP Redirect, in which case the performance
cost of ICMP Redirect is incurred while the benefits are wasted.
If you add or change more than one IP interface associated with the same
VLAN, disable the ICMP Redirect option for optimal performance.
If you disable ICMP Redirect, the hardware routes the frame, and no
messages are sent back to the sending device. At some point,
however, the number of retries associated with less intelligent
hardware routing overtake any benefits that are associated with the
speedier routing that hardware provides.
To maximize the effectiveness of ICMP Redirect, have ICMP Redirect
on the system that is connected to the greatest number of other
routing devices.