128
• The selected route is not destined for 0.0.0.0.
• There is no source route option in the received packet.
ICMP redirect messages simplify host management and enable hosts to gradually optimize their
routing table.
Procedure
1. Enter system view.
system-view
2. Enable sending ICMP redirect messages.
3.
ip redirects enable
By default, the sending of ICMP redirect messages is disabled.
Enabling sending ICMP time exceeded messages
About ICMP time exceeded messages
A device sends ICMP time exceeded messages by following these rules:
• The device sends the source an ICMP TTL exceeded in transit message when the following
conditions are met:
{ The received packet is not destined for the device.
{ The TTL field of the packet is 1.
• When the device receives the first fragment of an IP datagram destined for it, it starts a timer. If
the timer expires before all the fragments of the datagram are received, the device sends an
ICMP fragment reassembly time exceeded message to the source.
Restrictions and guidelines
If the ICMP time exceeded message sending is disabled, the device does not send ICMP TTL
exceeded in transit messages. However, it can still send ICMP fragment reassembly time exceeded
messages.
Procedure
1. Enter system view.
system-view
2. Enable sending ICMP time exceeded messages.
3.
ip ttl-expires enable
By default, the sending of ICMP time exceeded messages is disabled.
Enable sending ICMP destination unreachable messages
About ICMP destination unreachable messages
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 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 packet is destined for the device.
{ The transport layer protocol of the packet is not supported by the device.
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