cannot ping to macbook pro

I can't get my macbook accessable for other computers in my local network. I have the following setup:

router: airport extreme base station
macbook pro(3,1) with mac os x (10.5.8)

I set the Security option to allow all incoming traffic.
I set the Sharing options to allow for external ssh login.

I can login from the macbook to an another computer in my network with ssh (for example to a linux based nas). If I try to ping to the macbook (with the correct ip address) the pinging fails. Also an ssh fails:

+[~] # ssh -vvv 10.0.1.6+
+OpenSSH_4.6p1, OpenSSL 0.9.7a Feb 19 2003+
+debug2: ssh_connect: needpriv 0+
+debug1: Connecting to 10.0.1.6 [10.0.1.6] port 22.+
+debug1: connect to address 10.0.1.6 port 22: Connection timed out+
+ssh: connect to host 10.0.1.6 port 22: Connection timed out+

It occurs both with wireless and wired connection.

I checked with sysctl the status of the ipfw firewall and turned it off:

+$ sysctl net.inet.ip.fw.enable+
+net.inet.ip.fw.enable: 1+
+$ sudo ipfw disable firewall+
+$ sysctl net.inet.ip.fw.enable+
+net.inet.ip.fw.enable: 0+

However, after changing this setting still a ping is not possible. Also if I reboot the ipfw firewall is turned on again.

I rebooted the macbook with an ubuntu livecd and checked if it was possible to access it with ssh. In that case it works fine so my conclusion is that the problem is somewhere in the mac os x setup, the router is configured ok.

Any ideas what to do? Is there a possibility to turn ipfw permanently off? Also do I have to check other things?