Question about Routing Headers

[Lori Napoli <lanapoli at us.ibm.com>]

I have a question about Routing Headers
(type 0), more specifically what happens when we receive an ICMPv6 msg
where the offending packet contained a routing header.  From RFC 3542,
 a routing header can contain 127 IPv6 next hop addresses.  Therefore,
if a packet specified the maximum number of entries in a routing header,
the routing header alone would exceed 1280 bytes.   Now, if an intermediate
node needed to drop this packet and generate an ICMPv6 msg,  the ICMPv6
msg can only contain as much of the offending packet as will fit within
minimum MTU (1280 bytes).  Therefore it is possible for the offending
packet within the ICMPv6 msg to not contain the entire routing header.
 This ICMPv6 msg will be sent to the original source of the packet,
but the source address of the ICMPv6 msg will not be the original destination
address of the packet since the destination address in the IPv6 header
changes when there is a routing header.  So, how does the originating
node correlate this ICMPv6 packet with the correct socket?  Since
we can't rely on the entire routing header being present in the offending
packet, we can't even rebuild what the original destination would have
been.

My second question is that for IPv6,
the Type 0 Routing header can contain 127 addresses.  This routing
header is considered non-fragmentable.  If your interface is Ethernet
with a standard 1492 MTU, this packet cannot be sent on that interface
since the routing header alone would exceed 1492.  It seems inconsistent
to me to allow such a large non-fragmentable header.  


Lori
e-mail: lanapoli@us.ibm.com