On 18 Mar 2004 at 14:34, John Kemp wrote:

> Sue, Check the little things first. Are the IP's correct. Are the netmasks
> identical. If the answer is yes - are you running a firewall with the Port 7
> blocked. The ping command falls under the ICMP protocol. Port 7 should be
> the echo port for ICMP.
>
> Bon Chance...John

  Port numbers are sub-selections within the UDP and TCP protocols.  Within
TCP, port 7 is allocated for an "echo" service, but this is rarely used and
should, in fact, be disabled.  (It turns out that leaving it enabled permits
some easy/nasty ways to kill a machine.)
  The "ping" command uses a different protocol, ICMP, which doesn't use port
numbers.  ICMP uses type and subtype values; ping uses the "echo request"
and "echo reply" types.

  It's certainly *possible* that a firewall is blocking this, but the only
time I've ever heard of that on an individual machine software firewall, it
was the XP built-in firewall (have we eliminated that in this case?), and it
was only blocking pings to the default gateway -- in this case, that would
mean that the ICS machine should still be able to ping the other....

David Gillett

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