"Dan Langille"<dan.langille@dvl-software.com> wrote:
> JB <nobody@example.org> wrote
>
> >FWIW with NetMeeting, Iphone5, ICQ file transfers, these can sometimes
> >work if you do the calling and sending the other way round forget it.
>
> This sounds very much like the DCC problems when using IRC behind a
firewall.
> In the DCC case, the problem is not the firewall, it's the IRC protocol
itself.
May I ask what DCC means in this context?
> The protocol assumes the computer you are talking to is the on with the IP
> it sees. This is not the case with firewalls. The IP you see is that of
the
> firewall. The actual computer is behind the firewall.
Just to expand this, protocols which embed IP addresses within the data
payload need special treatment when Network Address Translation (NAT) is used.
(And firewalls do not always use NAT, NAT is used in the M10 Router)
The most infamous example is FTP where the IP address of the requesting host
is embedded, in ASCII, within the data, rather than address portion of the IP
packet. FTP is well understood, and so pervasive that almost every NAT
implementation examines request packets, replaces the ASCII IP address in the
packet with the NAT'ed address, recalculates checksums, etc. etc. and sends it
on it's way.
NAT implementations do vary, and I've been told, repeatedly, by some Cisco
advocates, that Cisco's NAT is much more comprehensive (and potentially much
more expensive) than the M10 implementation. It understands how to correct
more protocols, including the Netmeeting one (or so I am told).
I think Dan is absolutely correct that the problem here is shared between the
protocol (and in these days of dwindling IPv4 address availability and the
popularity of NAT, it's a pretty dull protocol that does this sort of
nonsense) and the implementation of NAT on the M10.
A solution, which I understand from various sources is available, would be to
go for the internal ADSL modem, which not being a router will serve a single
PC, but the public IP address, which is on the ADSL side of the M10, will
instead be "on" the PC, and so the embedded IP address will be correct.
(And this means that you can choose your own router software and NAT
implementation, and have other machines on the "inside" of that PC, if you
have the skill, money or time to have that implemented.)
> Dan Langille
Hamish.
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Received on Wed Jul 7 22:58:53 1999