iptables + gre + masquerade = doesn't work?

[MichealC4]

I have a server that is is behind a GRE tunnel. This much works. I can get to the server with the GRE tunnel. What doesn't work is then a masquerade setup that works without the gre tunnel.

So this is what things look like:

GRE-->iptables-->server

^ Entry here ends at iptables
^ Entry here correctly ends at server

I can get to the final server through the iptables with my existing iptables setup. I can get to the iptables from the GRE tunnel. I can't get all the way through. Here are what my iptables look like:

iptables -t nat -A PREROUTING -p tcp --dport ' + $port + ' -j DNAT --to-destination ' + $ip + ':' + $port
iptables -t nat -A PREROUTING -p udp --dport ' + $port + ' -j DNAT --to-destination ' + $ip + ':' + $port
iptables -t nat -A POSTROUTING -j MASQUERADE

This works just fine as-is. I don't currently disallow any traffic, so protocol 47 isn't blocked.

I can't for the life of me figure out why this doesn't work with the GRE. Any ideas?

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"Will work for bandwidth" - Thinkgeek T-shirt

 

[MichealC4]

Looks like spaces aren't respected:

GRE-->iptables-->server

^ Entry here ends at iptables
......^ Entry here correctly ends at server


----------------------------
"Will work for bandwidth" - Thinkgeek T-shirt