Configuring ICMP Redirects
20-10 IP Configuration
This example shows how to enable IP directed broadcasts on VLAN 1 and have all client DHCP
requests for users in VLAN 1 to be forwarded to the remote DHCP server with IP address
192.168.1.28
C5(su)->router(Config)#interface vlan 1
C5(su)->router(Config-if(Vlan 1))#ip directed-broadcast
C5(su)->router(Config-if(Vlan 1))#ip forward-protocol udp
C5(su)->router(Config-if(Vlan 1))#ip helper-address 192.168.1.28
Configuring ICMP Redirects
You can disable or enable sending ICMP redirect packets to the switch CPU for processing, at a
global level and at an interface level. By default, sending ICMP redirects is enabled globally and
on all interfaces. Disabling sending ICMP redirects can reduce CPU usage in certain deployments.
Use the ip icmp redirect enable command to enable or disable sending ICMP redirects to the CPU
for processing. The no form of the command disables sending ICMP redirects to the CPU.
Use the show ip icmp redirect command to display the status of sending ICMP redirects.
This example disables sending ICMP redirects on the interface VLAN 5 and then displays the
ICMP redirect status for VLAN 5
C5(su)->router#configure
C5(su)->router(Config)#interface vlan 5
C5(su)->Router1(Config-if(Vlan 5))# no ip icmp redirect enable
C5(su)->Router1(Config-if(Vlan 5))#exit
C5(su)->router(Config)#show ip icmp redirect interface vlan 5
Vlan Id Admin Status
------- ------------
5 Disabled
Terms and Definitions
Table 20-3 lists terms and definitions used in this IP routing configuration discussion.
Note: On the A4 platforms, you can only enable or disable ICMP redirects at an interface level, not
at a global device level.
Table 20-3 IP Routing Terms and Definitions
Term Definition
Address Resolution
Protocol (ARP)
A protocol providing a method for finding a MAC hardware address when only the IP
address is known.
ARP proxy Provides for the ability of a device on a given network to answer the ARP queries for
a network address that is not on that network.
broadcast
forwarding
Provides for the ability for rout UDP broadcasts in order to provide services to clients
on a different subnet than the one originating the broadcast.
directed broadcast The ability to address a destination host such that the arriving packet will be
broadcasted to the network as if it was a normal broadcast generated by the
receiving host.
IP address An address used by the IP protocol to identify a routing interface or routing device.
IP address helper The ability to specify the IP address the UDP forwarded packet should be sent to.
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