Since we route WITHIN a RPL network, rather than THROUGH a RPL
network, it would seem that the case mentioned does not arise. Right?
On May 30, 2010, at 7:56 AM, Erik Nordmark wrote:
The draft says:
A RPL Router MAY insert a Type 4 Routing header if one does not
already exist. The conditions for inserting a Type 4 Routing header
are out of scope of this document.
Having routers insert headers in packets they forward is know to be
problematic in general, since it breaks path MTU discovery.
Taking an example of a host which sends a packet which is 1500
bytes, and then receives an ICMP packet too big error saying "please
limit packets to 1500 bytes", will not change the host's behavior.
But that can happen if some router grows the packet to be more than
1500 bytes.
Thus in general, the only safe way to insert headers in a packet is
to have the "inserter" put an extra IP header, with itself as a
source, then the inserted header, and then the original packet.
That extra IP header ensures that any ICMP error go back to the
"inserter", which can then compensate for its insertion before
sending the ICMP error towards the sender of the original packet.
Thus I think there is a question for 6man whether we think the
constrained environment of ROLL is such that we can relax this. But
it does require that all the routers at the edge of the ROLL network
adjust the ICMP errors they forward to compensate for any inserted
RH4 headers.
Erik
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