[TriLUG] RedHat 8.0 / IPTables / GRE packets?

[Jon Carnes]

I was under the impression that IPTables didn't handle GRE yet, but this
link would tend to indicate that it has limited abilities.

http://lists.netfilter.org/pipermail/netfilter-devel/2002-March/006956.html


On Tue, 2002-12-10 at 14:27, prhodes at vdsinc.com wrote:
> Question for you network / linux guru's...
> 
> I'm using RedHat 8.0, and trying to connect to a poptop server.  The poptop
> server
> is also an iptables based firewall, providing masquerading for the rest of
> my
> network, from the cable modem...
> 
> The problem is, I can't establish a connection to the poptop server from my
> office.
> I have (I think) narrowed the problem down to pptpd not receiving the
> config-req response
> from the client.  This appears to be because the GRE packets aren't getting
> through.
> 
> I have a line in my iptables script which is supposed to allow GRE
> 
> iptables -A INPUT -p 47 -i eth0 -s 0/0 -j ACCEPT
> 
> but it still doesn't work.  Curiously enough, even if I try to log incoming
> GRE packets
> 
> iptables -A INPUT -p 47 -i eth0 -s 0/0 -j LOG
> 
> I don't see anything in the log from an attempted connection.  However, if
> I run
> tcpdump on eth0 and watch the raw packets when I try a connection, I see
> GRE packets come in.  It's almost like iptables isn't recognizing the GRE
> packets.
> 
> Does anybody know if there's anything else special I need to do to
> make this work?  If so, please do tell....
> 
> Thanks,
> 
> Phillip Rhodes
> Application Designer
> Voice Data Solutions
> 919-571-4300 x225
> prhodes at vdsinc.com
> 
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