Tiger Server firewall issues - forwarding protocol 47 (GRE) for VPN access

Question

Hi everybody,
I'm trying to allow VPN access to my Mac Pro running 10.4.10 Server. I've allowed the TCP and UDP ports, but the sticking point is this: the client tries to connect but I get a bunch of these in the firewall log:
Deny P:47 xxx.xxx.xxx.xxx(address initiating VPN) 10.0.100.222(MacPro local address) in via en0
After doing some research I figured I needed to allow protocol 47 (GRE) and so tried to add a rule via the "Advanced" tab for firewalls in server manager. I click the + button, select allow, leave the other field, select GRE, and then select from:any and to:any and the in dropdown. When I try to save and activate the rule, however, it complains that there is an error and that all subsequent rules are skipped. I've tried all the possible variations (within my parameters, of course) but it won't work.
Manually inspecting the /etc/ipfw file shows the rule added but without a specification for the GRE or protocol 47 part. i.e.:
add 1050 allow from any to any in
(This looks a little like a server manager bug to me, but I digress)
So I tried manually editing the file in /etc/ipfilter but no joy.
Being somewhat new to OSX I am getting flustered. Am I completely misunderstanding something here? While a search on "VPN GRE firewall" turns up about million hits, none seem applicable to my situation. Thanks in advance.

Answer 1

Try using the "Services" tab, selecting "any" (for example) and configuring the rule there.
The "Advanced" section will allow you to add rules that don't already exist, but there is already a rule for GRE so that might, possibly have something to do with the error you're getting.