Cannot access IP address from another subnet

[Seak]

    This is very very odd.  What O/S is in your PC B?  Beside PC C can't
ping PC B, can PC C open a VNC connection to PC B (normally the answer
should be No)?

    Have you triggered some firewall by mistake in PC B?

Javier Sheh wrote:
> Hello,
>
> I have 3 PC's in 3 different subnets in my intranet.  PC A has IP
> address 135.21.42.108, PC B has IP address 135.16.102.30, PC C has IP
> address 135.91.108.36.  I loaded RealVNC Free Edition 4.1.1 server on
> B.  I loaded RealVNC Free Edition 4.1.1 client on A.  No RealVNC was
> on C.  Before loading RealVNC, I was able to ping from A to B and from
> C to B.  I established RealVNC connection from A to B.  After this, I
> tried pinging from C to B, but could not get response from B.  C could
> ping anything on B's subnet (e.g. 135.16.102.50, 135.16.102.1) except
> B itself.  I rebooted PC A and PC B, but still could not get to PC B
> through C.  I tried another PC on subnet same as C and could not ping
> PC B either.  Is RealVNC establishing some kind of pipe that prevents
> other subnets from accessing a specific server address?  What can be
> done to clear this problem?  Is there some kind of option I am
> overlooking?  Am I closing the connection improperly?
>
> I have noticed this with two other IP addresses that I used RealVNC
> with.  These IP addresses cannot be pinged from a foreign subnet.
>
> Thanks,
> Javier