On 11/30/05, Heath Henderson <email@hidden> wrote:
> Port 47 is your GRE port. You have to have this open for PPTP VPN connections to work correctly (at least with Windows).
No, no, no. GRE uses neither TCP nor UDP; it doesn't use TCP/UDP
ports at all. It's IP protocol 47, /beside/ TCP, not above it. Same
with ESP. ESP can be tunnelled over UDP (NAT traversal) if needed,
but that doesn't make it a UDP protocol.
I've seen this problem twice on the list, recently, for people using
VPNs, assuming that a string like P:47 means a TCP port somehow (when
virtually all other reference material, even ipfw itself, uses
x.x.x.x:yy to denote a TCP or UDP port yy, instead).
I know it's tempting to just turn on a service without really knowing
what it does, but when dealing with VPNs and firewalls for security,
one really should at least do their homework. This is fundamental IP
theory -- nothing strange, even if you've never used GRE before.
I wonder how many firewalls out there have TCP/UDP ports 47 and 50
open for no reason..
J.
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