How to detect whether firewall service is provided by server or by ISP?

[martin <m4rtin86 () gmail com>]

I have two servers behind different networks. First network is
protected with firewall provided by the router and there is no
firewall in the server:

[root@martin ~]# nmap --reason -n -PN -p445 192.168.217.73

Starting Nmap 5.00 ( http://nmap.org ) at 2010-09-16 13:57 EEST
Interesting ports on 192.168.217.73:
PORT    STATE    SERVICE      REASON
445/tcp filtered microsoft-ds no-response

Nmap done: 1 IP address (1 host up) scanned in 2.15 seconds
[root@martint ~]#

The other server is in the second network and there is no firewall
service provided by the router, but firewall is activated in the
server:

[root@martin ~]# nmap --reason -n -PN -p9731 192.168.13.19

Starting Nmap 5.00 ( http://nmap.org ) at 2010-09-16 13:56 EEST
Interesting ports on 192.168.13.19:
PORT     STATE    SERVICE REASON
9731/tcp filtered unknown no-response

Nmap done: 1 IP address (1 host up) scanned in 2.15 seconds
[root@martin ~]#

Is there somehow possibility to detect, whether firewall is active in
the server or in the router?

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