R0106-HP MSR Router Series Layer 3 - IP Services Command Reference(V7)

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• 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 time exceeded message to the source.
A device disabled from sending ICMP time exceeded messages does not send ICMP TTL exceeded in
transit messages but can still send ICMP fragment reassembly time exceeded 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 an ICMP network unreachable 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 an ICMP protocol unreachable 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 an ICMP port unreachable 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 an ICMP
source route failed 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 an ICMP fragmentation needed and DF set message.
Examples
# Enable sending ICMP destination unreachable messages.
<Sysname> system-view
[Sysname] ip unreachables enable