[CentOS] 2 questions on CentOS firewall

[Timothy Murphy]

Timothy Murphy wrote:

> Ljubomir Ljubojevic wrote:
> 
>>> (1) I can open port 22 on the Billion, allowing me to ssh in from
>>> outside. But for some reason I cannot ping the same address from
>>> outside.
> 
>> This is due to modem refuses to answer to pings. You might have option
>> to allow it in modem config.
>> 
>> Ping (ICMP) does not use ports but it is packet of type 8.
> 
> Thanks again for your response.
> Could CentOS be preventing me from pinging the system?

Further to my question,
how can I determine if it is the Billion 5200S modem/router
that is preventing pings, or if it is the CentOS-6 MicroServer
attached to the modem/router?

I don't see any reference to ICMP on the modem web-page.

On the other hand the CentOS firewall seems to allow ICMP
unless explicitly rejected (which I haven't done).

Surely it would be slightly odd for a modem/router
to reject pings by default?

Is there any simple way, short of using something like ethereal,
of determining if ICMP packets are reaching the computer,
and being rejected there?



-- 
Timothy Murphy  
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland