Re: 10.1.1.1 up?

["Steven Alexander" <steve () cell2000 net>]

----- Original Message ----- 
From: <jaye_gettes () hushmail com>
To: "Chad Loder" <cloder () loder us>; <nmap-dev () insecure org>
Sent: Friday, May 30, 2003 8:11 AM
Subject: Re: 10.1.1.1 up?


> I thought -P0 was "do not ping first" in case programs like portsentry
> block you if you ping a host first?  Also, is it not the case that a
> host that is not pingable (because a fw blocks ping) could allow a tcp
> or udp port in?
>
> thanks

ping uses an ICMP packet.  ICMP, TCP and UDP are different protocols that
each use the IP protocol.  A firewall can selectively block any or all of
these.  It can also block some of each type but not others.  For instance, a
firewall could allow outgoing ICMP echo requests and incoming ICMP echo
replies but deny all other ICMP traffic in or out of the network.  This
would allow users on the internal network to ping outside hosts but would
not allow outside hosts to ping a machine on the network; it would also
disallow other ICMP traffic such as timestamps and redirects.

-steven


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