ip unreachables enable

Use ip unreachables enable to enable sending ICMP destination unreachable messages.

Use undo ip unreachables enable to disable sending ICMP destination unreachable messages.

Syntax

ip unreachables enable

undo ip unreachables enable

Default

Sending ICMP destination unreachable messages is disabled.

Views

System view

Predefined user roles

network-admin

mdc-admin

Usage guidelines

A device sends ICMP destination unreachable messages by following these rules:

• The device sends the source an ICMP network unreachable message when the following conditions are met:

  • The received packet does not match any route.

  • No default route exists in the routing table.

• The device sends the source an ICMP protocol unreachable message when the following conditions are met:

  • The received packet is destined for the device.

  • The transport layer protocol of the packet is not supported by the device.

• The device sends the source an ICMP port unreachable message when the following conditions are met:

  • The received UDP packet is destined for the device.

  • The packet's port number does not match the running process.

• The device sends the source an ICMP source route failed message when the following conditions are met:

  • The source uses Strict Source Routing to send packets.

  • The intermediate device finds that the next hop specified by the source is not directly connected.

• The device sends the source an ICMP fragmentation needed and DF set message when the following conditions are met:

  • The MTU of the sending interface is smaller than the packet.

  • The packet has Don't Fragment set.

Examples

# Enable sending ICMP destination unreachable messages.

<Sysname> system-view
[Sysname] ip unreachables enable