HPE 5900 series

162
Usage guidelines
A device sends ICMP time-exceeded messages by following these rules:
•
If a received packet is not destined for the device and the TTL field of the packet is 1, the device
sends an ICMP TTL Expired in Transit message to the source.
•
When the device receives the first fragment of an IP datagram destined for the device itself, it
starts a timer. If the timer expires before all the fragments of the datagram are received, the
device sends an ICMP Fragment Reassembly Timeout message to the source.
A device disabled from sending ICMP time-exceeded messages does not send ICMP TTL Expired in
Transit messages but can still send ICMP Fragment Reassembly Timeout messages.
Examples
# Enable sending ICMP time-exceeded messages.
<Sysname> system-view
[Sysname] ip ttl-expires enable
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
Usage guidelines
A device sends ICMP destination unreachable messages by following these rules:
•
If a packet does not match any route and there is no default route in the routing table, the device
sends a Network Unreachable ICMP error message to the source.
•
If a packet is destined for the device but the transport layer protocol of the packet is not
supported by the device, the device sends a Protocol Unreachable ICMP error message to the
source.
•
If a UDP packet is destined for the device but the packet's port number does not match the
running process, the device sends the source a Port Unreachable ICMP error message.
•
If the source uses Strict Source Routing to send packets, but the intermediate device finds that
the next hop specified by the source is not directly connected, the device sends the source a
Source Routing Failure ICMP error message.
•
If the MTU of the sending interface is smaller than the packet and the packet has a Don't
Fragment set, the device sends the source a Fragmentation Needed and Don't Fragment-Set
ICMP error message.
Examples
# Enable sending ICMP destination unreachable messages.
<Sysname> system-view