icmp redirect send

Usage Scenario

ICMP error packets contain network information, such as network connectivity, host reachability, and route availability. ICMP error packets are ultimately returned to the sender because the sender is the logical receiver of the ICMP error packets. The sender learns about the error types from the ICMP error packets, and then determines how to retransmit the data.

ICMP Redirect packets are a type of ICMP error packets.

When a host starts, there may be only one default route to the gateway in its routing table. In the following situations, the device functions as a gateway to send an ICMP Redirect packet to the source host, requesting the host to select another next hop address for subsequent packet forwarding:

• The interface that receives the data packet is the same as the interface used to forward the packet.
• The device needs to forward a received packet. After looking up the routing table, the device finds that the next hop IP address is on the same network segment with the destination address of the packet.

After the device sends ICMP Redirect packets to the host that has only a few routes, the host can enrich the routing table and find out the optimal route.

The ICMP error packets facilitate network control and management. However, the inherent defects of the ICMP protocol make the routing devices and hosts be prone to attacks. Therefore, sending the ICMP error packets has the following defects:

• The ICMP packets increase traffic volume and burden the network devices.
• If a device receives a large number of malicious attack packets and needs to return ICMP error packets, the device is busy handling ICMP packets, and the device performance is degraded.
• The ICMP Redirect function increases the number of routes in the host's routing table. When many routes are added, the host performance will be degraded.

You need to decide whether to enable ICMP Redirect packet sending according to network situation.

Precautions

The command is used on the interface that receives ICMP packets.