Cisco Systems WSC4500X16SFP Manual De Usuario
5-12
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter 5 Checking Port Status and Connectivity
Configuring ICMP
To enable the generation of ICMP Protocol Unreachable and Host Unreachable messages, enter the
following command in interface configuration mode:
following command in interface configuration mode:
To limit the rate that Internet Control Message Protocol (ICMP) destination unreachable messages are
generated, perform this task:
generated, perform this task:
Enabling ICMP Redirect Messages
Data routes are sometimes less than optimal. For example, it is possible for the router to be forced to
resend a packet through the same interface on which it was received. If this occurs, the Cisco IOS
software sends an ICMP Redirect message to the originator of the packet telling the originator that the
router is on a subnet directly connected to the receiving device, and that it must forward the packet to
another system on the same subnet. The software sends an ICMP Redirect message to the packet's
originator because the originating host presumably could have sent that packet to the next hop without
involving this device at all. The Redirect message instructs the sender to remove the receiving device
from the route and substitute a specified device representing a more direct path. This feature is enabled
by default.
resend a packet through the same interface on which it was received. If this occurs, the Cisco IOS
software sends an ICMP Redirect message to the originator of the packet telling the originator that the
router is on a subnet directly connected to the receiving device, and that it must forward the packet to
another system on the same subnet. The software sends an ICMP Redirect message to the packet's
originator because the originating host presumably could have sent that packet to the next hop without
involving this device at all. The Redirect message instructs the sender to remove the receiving device
from the route and substitute a specified device representing a more direct path. This feature is enabled
by default.
However, when Hot Standby Router Protocol (HSRP) is configured on an interface, ICMP Redirect
messages are disabled (by default) for the interface. For more information on HSRP, refer to the
following URL:
messages are disabled (by default) for the interface. For more information on HSRP, refer to the
following URL:
To enable the sending of ICMP Redirect messages if the Cisco IOS software is forced to resend a packet
through the same interface on which it was received, enter the following command in interface
configuration mode:
through the same interface on which it was received, enter the following command in interface
configuration mode:
Command
Purpose
Switch (config-if)# [no] ip unreachables
Enables ICMP destination unreachable messages.
Use the no keyword to disable the ICMP destination
unreachable messages.
unreachable messages.
Command
Purpose
Switch (config)# [no] ip icmp rate-limit
unreachable [df]
milliseconds
Limits the rate that ICMP destination messages are
generated.
generated.
Use the no keyword to remove the rate limit and
reduce the CPU usage.
reduce the CPU usage.
Command
Purpose
Switch (config-if)# [no] ip redirects
Enables ICMP Redirect messages.
Use the no keyword to disable the ICMP Redirect
messages and reduce CPU usage.
messages and reduce CPU usage.