
Chapter 12 • IPv6 Internet Control Message Protocol (ICMPv6) 221
“packet too big” message), there is no obvious way to detect a change that
increases the path MTU.
To remedy the situation, RFC 1981 recommends that implementations
cache PMTU values and have the values time out after some moderate
amount of time (10 minutes is the duration suggested). At that point, the
PMTU value can be recalculated.
In this way, packet size efficiency can be maximized. However, there are
some situations in which the path MTU value will never change. For
example, a node connecting to an FDDI network that is attached to the
global Internet through a small MTU fixed serial ...