Patton electronic SmartNode 4110 Series manual Icmp message processing, Icmp redirect messages

SmartWare Software Configuration Guide 10 • IP interface configuration

ICMP message processing

The IP suite offers a number of services that control and manage IP connections. The Internet Control Mes- sage Protocol (ICMP) provides many of these services. Routers send ICMP messages to hosts or other routers when a problem is discovered with the Internet header. For detailed information on ICMP, see RFC 792.

SmartWare supports the following ICMP message processing features:

•ICMP redirect messages

•Router advertisement broadcast message

ICMP redirect messages

Routes are sometimes less than optimal. For example, the router may be forced to resend a packet through the same interface on which it was received. In this case, an ICMP redirect message is sent to the originator of the packet telling 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 origina- tor of the packet 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.

ICMP message processing offers two options for host route redirects:

•accept—accepts ICMP redirect messages

•send—sends ICMP redirect messages

Mode: Interface

Step	Command	Purpose
1	node(ctx-ip)[router]#interface name	Selects the interface name for ICMP mes-
		sage processing configuration
2	node(if-ip)[name]#icmp redirect { accept send}	Enables to send or accept ICMP redirect
		messages

Example: ICMP redirect messages

The following example shows how to configure ICMP messages processing to accept ICMP redirect messages on the IP interface lan. Use the following commands in IP context configuration mode.

node(ctx-ip)[router]#interface lan node(if-ip)[lan]#icmp redirect accept

Router advertisement broadcast message

This message configures the behavior of the router when receiving an ICMP router solicitation message, and determines if the router shall send periodic ICMP router advertisement messages or not.

By default, ICMP router advertisement messages are sent, either as a reply to ICMP router solicitation mes- sages or periodically. If the feature is disabled, ICMP router advertisement messages are not sent in any case, neither as a reply to ICMP router solicitation messages nor periodically.

IP interface configuration task list 124