I start ppp manually. I don't mind adding the rule by hand - presumably, it's just one line? The client is a laptop, I am connected to the internet via the Dlink router and a cable modem (PPPoE).
I start thinking that this is not a firewall problem, but something related to routing. Shorewall blocked traffic on only one occasion. After I stopped, and then enabled shorewall, messages from it stopped. I still cannot connect to the Exchange server at work regardless whether shorewall is on or off.
After connection is established, I can see that the routing table changes to
CODE
# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
xxx.yyy.zzz.90 0.0.0.0 255.255.255.255 UH 0 0 0 ppp0
192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 0 wlan0
0.0.0.0 192.168.0.1 0.0.0.0 UG 0 0 0 wlan0
where xxx.yyy.zzz.90 is the address of the gateway. Also, ifconfig shows that ppp interface is up
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ppp0 Link encap:Point-to-Point Protocol
inet addr:xxx.yyy.zzz.92 P-t-P:xxx.yyy.zzz.90 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1000 Metric:1
RX packets:12 errors:1 dropped:0 overruns:0 frame:0
TX packets:11 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:261 (261.0 b) TX bytes:134 (134.0 b)
This tells me that the tunnel is established OK. However, I cannot connect to the exchange server on the xxx.yyy.0.0 network - I am prompted to type in the password, and then I get an error message saying that the authentication failed.