R3102-R3103-HP 6600/HSR6600 Routers Layer 3 - IP Services Command Reference

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• A host's performance degrades if the redirection function increases the size of its routing table.
• End users are affected if malicious users send ICMP destination unreachable packets.
To prevent such problems, disable the device from sending ICMP error packets.
Configuration procedure
To enable sending ICMP error packets:
Step Command Remarks
1. Enter system view.
system-view N/A
2. Enable sending ICMP
error packets.
• Enable sending ICMP redirect
packet:
ip redirects enable
• Enable sending ICMP timeout
packet:
ip ttl-expires enable
• Enable sending ICMP destination
unreachable packet:
ip unreachables enable
Disabled by default.
When sending ICMP timeout
packets is disabled, the device
does not send "TTL timeout" ICMP
error packets. However,
"reassembly timeout" error packets
are sent correctly.
Enabling support for ICMP extensions
ICMP messages are of a fixed format and cannot carry extension information. With support for ICMP
extensions enabled, a device appends an extension information field to the ICMP messages as needed.
The device can append only MPLS label information to ICMP messages.
ICMP extensions for MPLS
In MPLS networks, when a packet's TTL expires, MPLS strips the MPLS header, encapsulates the
remaining datagram into an ICMP time exceeded message, and sends the message to the egress router
of the MPLS tunnel. Then the egress router sends the message back to the ingress router of the tunnel. The
ICMP message, however, does not contain the label information that is very important to the ingress
router. With support for ICMP extensions enabled, the device appends the MPLS label to the ICMP time
exceeded message before sending it back to the ingress router of the tunnel.
ICMP extensions are usually used for an enhanced traceroute implementation in MPLS networks, in
which MPLS label information about each hop the original datagram arrives at is printed.
Handling ICMP messages
ICMP messages can be classified into the following types:
• Common ICMP messages—Without any extension information.
• Extended ICMP messages with a length field—Carry extension information and a length field. The
length field indicates the length of the original datagram that is encapsulated within the ICMP
header and excludes the ICMP extension length. Such an ICMP message complies with RFC 4884.