Re: Problem setting up poptop on RHEL5

On Thu, Sep 01, 2011 at 11:29:14AM +1000, Steve Phillips wrote:
> I guess I was asking if there was a way to specify the source IP for
> the GRE packets.

When the control connection arrives on port 1723, the getsockname
syscall is used to obtain the IP address of the local end of the
connection.  pptpctrl.c:173.

This IP address is then used in the bind syscall so that the GRE packets
will have the same source IP address.  pptpgre.c:87

So please use tcpdump and confirm the connections are going to the
correct IP address?

> From looking at the ip_gre.c module in the linux kernel source,
> there appears to be an option to set the outbound source IP, I'm
> just wondering if this was actually implemented or if it simply fell
> back to the default 'use the primary IP regardless of whether its
> the right one or not'

We don't use ip_gre.c in the Linux kernel source.  That's an entirely
different implementation ... for IP in GRE tunnels.  PPTP is IP in PPP
in GRE.

> (and then there is the weird problem that if I actually bind/connect
> to .170 I get the "GRE: xmit failed from decaps_hdlc: Operation not
> permitted "

That's interesting.  It means a write to the socket failed.  Are you
sure you are root?  Are capabilities enabled in the kernel?

-- 
James Cameron
http://quozl.linux.org.au/

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