HP-UX TCP/IP Performance White Paper, March 2008

ICMPv6:

33 calls to generate an ICMPv6 error message

8 ICMPv6 messages dropped

12 ICMPv6 error messages dropped for rate control

In IPv6, in order to limit the bandwidth and forwarding costs incurred by originating ICMPv6 error

messages, an IPv6 node limits the rate of ICMPv6 error messages it originates. This situation may occur

when a source sending a stream of erroneous packets fails to heed the resulting ICMPv6 error messages.

One can use ndd to alter ICMPv6 error message rate control via the ip6_icmp_interval tunable.

Output histogram:

destination unreachable: 8

administratively prohibited: 1

An ICMPv6 destination unreachable message comes in several types. Some imply that there was no

application waiting at that port number. Others could be generated when there is no route to the

destination or, when the packet has to be forwarded but IPv6 forwarding is not enabled. One can use ndd

to alter IPv6 forwarding via the ip6_forwarding tunable.

time exceeded: 3

This statistic will be incremented in two cases:

• The system is acting as a router and the Hop-Limit field in an IPv6 datagram to be forwarded has

reached zero. Increasing values of this statistic can imply two things – first, that the Hop-Limit value

being used by the system sending the datagrams is too small; ; second, that there is a routing loop

somewhere in the network. When there is a routing loop, the IP datagrams go around and

around, with their Hop-Limit’s decrementing at each router until they hit zero.

• Fragment reassembly timeout. One can use ndd to alter the fragment reassembly timeout via the

ip6_fragment_timeout tunable.

parameter problem: 1

An ICMPv6 parameter problem is generated if an IPv6 node processing a packet finds a problem with a

field in the IPv6 header or extension headers such that it cannot complete processing the packet.

packet too big: 1

An ICMPv6 Packet Too Big is sent by a router in response to a packet that it cannot forward because the

packet is larger than the MTU of the outgoing link.

echo: 6

echo reply: 19

An “echo” and “echo reply” are ICMPv6 informational messages. Traditionally, an “echo” is sent by using

ping utility.