PPTP Passthru

[Bob]

Archived from groups: comp.dcom.vpn,microsoft.public.windowsxp.work_remotely (More info?)

On the cheaper SOHO NAT routers, like the Linksys BEFSR4 and Netopia
Cayman 3546, there is a thing called PPTP Passthru or equivalent.

It's purpose it to allow Protocol 47 (GRE) packets to pass thru the
router so the PPTP VPN will work. You also have to forward port 1723
to a specific machine on the LAN where your VPN connection will be
established.

My question to you remote networking geniuses is:

How does the router know that what the specific VPN machine is for
purposes of PPTP Passthru? Or does the router just pass all GRE
packets to all LAN machines and let the one which has the VPN
capability sort it out?


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[Guest]

Archived from groups: comp.dcom.vpn,microsoft.public.windowsxp.work_remotely (More info?)

"Bob" <spam@spam.com> wrote in message
news:40780238.58522170@news-server.houston.rr.com...

> How does the router know that what the specific VPN machine is for
> purposes of PPTP Passthru? Or does the router just pass all GRE
> packets to all LAN machines and let the one which has the VPN
> capability sort it out?
>
I think the latter, but I'm not sure.

Here's a good reference, including all the RFC numbers at the end:

http://www.networksorcery.com/enp/protocol/gre.htm

A (possibly) good place to ask a question like this is
comp.dcom.lans.ethernet

This isn't an ethernet question, though, its an IP question, so I don't know
whether they'd answer or just say go elsewhere.

Looking at RFC 2637, 1.3.2, there's a key in each GRE packet indicating what
session the PPP packet belongs to.

 

[Sameer]

Archived from groups: comp.dcom.vpn,microsoft.public.windowsxp.work_remotely (More info?)

since these are NAT boxes, you need to do port fowarding telling the device
what to do with/where to direct incoming tcp/1723 traffic.

for example, on my setup, my broadband router redirects 1723 to an interface
on my firewall, which again redirects it to my VPN server.