Date   : Tue, 11 Aug 2009 16:34:02 +0100
From   : robert@... (Rob)
Subject: Econet <> Ethernet

2009/8/11 Pete Turnbull <pete@...>:
> On 11/08/2009 11:37, Phil Blundell wrote:
>
>> I just checked the manual for my router (a Speedtouch 536) and you're
>> right: it can forward UDP or TCP, but it doesn't seem to have any
>> provision for forwarding other IP protocols.
>
> I'd be surprised if that's strictly true, partly because I know that
> people have linked them to other routers in various ways for various
> reasons. ?For example I'd be very surprised if it doesn't forward ICMP
> (protocol 1), and it might forward IGMP (proto 2) and even GRE (47)

I suspect you are talking at cross purposes..

Every domestic router I have com across has allowed pretty much
everything to pass through it in an *outward* direction (LAN -> WAN)
but most only have very limited facilities to patch through incoming
connections.  Typically you specify a protocol and port to be listened
to on the WAN interface, and an IP address (and port, if you are
lucky) on the LAN side to which traffic is passed.  It's usually this
functionality which is restricted, and usually only allows UDP and TCP
protocols.

I've also encountered routers with even more restrictive use: e.g.
some will only forward to ports on the actual subnet on the lan side
(rather than any random address) or, worse, the one supplied by Sky
which stopped letting anything not on the immediate LAN subnet onto
the internet, after one particular firmware update..