[nzlug] Uncommon Transport Protocols + Linux

[Martin D Kealey]

On Fri, 5 Jan 2007, Daniel Pittman wrote:
> Raimund Eimann <raimund at cs.auckland.ac.nz> writes:
> > I suppose that packets with uncommon transport protocols or, more
> > precisely protocol numbers for which no handler (such as a TCP stack)
> > exists on a host are simply dropped on arrival?
>
> No -- they should have an ICMP error generated informing the sender that
> the protocol in question is not supported.

Err ... mais si! Look a level further down the protocol stack if you will...

We're talking about things *other than IPv4*. Sending an IPv4 response won't
help anyone.

In practice yes, such packets are discarded at the ethernet driver level.

In theory one could set the ethernet NIC to scan the protocol type as well
as the MAC address and drop unrecognised packets before even the driver gets
them, but I haven't looked at the Linux source to see if it does this. (And
of course, you'd need a NIC that supported such extended matching.)

-Martin