HPE FlexNetwork HSR6800 Configuration Manual page 203

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.
•
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.
NOTE:
If a DHCP enabled device receives an ICMP echo reply without sending any ICMP echo
requests, the device does not send any ICMP protocol unreachable messages to the
source. For more information about DHCP, see Layer 3—IP Services Configuration Guide.
The device sends the source an ICMP port unreachable message when the following
conditions are met:
− The UDP packet is destined for the device.
− The packet's port number does not match the corresponding 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 DF set.
To enable sending ICMP error messages:
Step
1. Enter system view.
2. Enable sending ICMP
error messages.
Sending ICMP error messages facilitates network management, but sending excessive ICMP
messages increases network traffic. The device performance degrades if it receives a lot of
malicious ICMP messages that cause it to respond with ICMP error messages.
Command
system-view
•
Enable sending ICMP redirect messages:
ip redirects enable
•
Enable sending ICMP time exceeded
messages:
ip ttl-expires enable
•
Enable sending ICMP destination
unreachable messages:
ip unreachables enable
190
Remarks
N/A
The default settings are
disabled.