Hi,
I am sending to both the lists as it may be relevant.
It seems that forwarding packets between two tunnels (either IPv4
over IPv4 or IPv6 over IPv6 or IPv6 over IPv4 tunnels ) can cause
unneeded exchange of packets till the ttl becomes zero. Following
is the sequence and wondering whether the RFCs that deal with
this should clarify :
There are two tunnels A and B on a router. Assume packet enter
tunnel A and get forwarded out of tunnel B. Let's assume
IPv6 over IPv4 tunnel.
1) Packet enters tunnel A, decapsulated and gets forwarded over
tunnel B where the packet is encapsulated in IPv4.
2) There is no route for this IPv4 packet as determined by the
IPv4 routing table. An ICMPv4 error is generated.
3) The ICMPv4 error is converted to an ICMPv6 error so that it can
be sent to the original IPv6 sender.
4) This gets forwarded over tunnel A where the ICMPv6 error gets
encapsulated in IPv4.
5) There is no route for this IPv4 packet [which is actually an ICMPv6
error] as determined by the IPv4 routing table. An ICMPv4 error is
generated.
6) The ICMPv4 error is converted to an ICMPv6 error so that it can
be sent to the original IPv6 sender [router itself].
Note that step (5) and step (6) are the similar to step (2) and (3)
and will continue forever till the ttl drops to zero.
At step (5) we are generating an ICMPv4 error for the ICMPv6 error.
At step (6) we are generating an ICMPv6 error for the ICMPv6 error.
Should step (5) or step (6) detect this and drop the packet ?
Does any implementation handle this case ? Should this be clarified
in the relevant RFCs ?
-mohan
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