Example - 3Com corebuilder 3500 Implementation Manual

Example

150.101.117.254
System 1
(255.255.255.0)
(ICMP redirect
enabled)
1
Host A
Disable ICMP Redirect if you have overlapped IP interfaces on ports
that are not configured to use 802.1Q VLAN tagging. Doing so
provides better routing performance between the overlapped subnets.
If you have two interfaces that belong to different VLANs that share a
given port and you want to completely disable ICMP redirects for that
port, disable the redirects for each interface that shares that port. If
you disable ICMP Redirect for only one interface and enable it for the
other, you may not get the performance improvement that you want.
Figure 57 shows how ICMP Redirect works.
Figure 57 ICMP Redirect Example
2
150.101.117.2
(255.255.255.0)
Default Gateway for Host A = 150.101.117.254
1
2
3
4
System 2
150.101.117.253
(255.255.255.0)
= Host A pings 150.101.119.2
= ICMP redirect on System 1 returns information about
the better route (150.101.117.253) to Host A. Host A
puts the better route into its routing table.
= System 1 routes the request to the correct address
= Second ping from Host A goes directly to 150.101.119.2
ICMP Redirect
150.101.119.2
3
4
293