VNC over different subnet mask
Fri Jun 20 13:23:00 2003
> -----Original Message-----
> From: firstname.lastname@example.org
> We've just run out of IP addresses on our network, so we're
> moving to a different scope,
Should be a totally different scope, not just an other netmask, also an
other network. Then the routers can do a lot for you, now you only have to
hope your routers can coop with the stuff.
If you use a totally different network, then just connect the same router
with a second port to the same network. configure this new port as one (the
gateway) of the new network and off you go.
> current IPs are running
> 192.168.60.1 - 255 the
Wild guess: subnet was 255.255.255.0?
That makes the next pre-defined (not for host usable) addresses:
The available host range: 192.168.60.1 - 192.168.60.254
prefered hosts (not requred, its just most tools provide this as default
values once the address and netmask of the above network is defined):
gateway: 192.168.60.254, network services (dns, dhcp etc): 192.168.60.1
> new scope is 192.168.61.1 - 255. and subnet mask 255.255.248.0
The available host range: 192.168.56.1 - 192.168.63.254 with the prefered
hosts on the boundaries as before. It is perfectly acceptable to use other
addresses for the gateway and the network services,
You see, the network address and the broadcast address of one network are
host addresses on the other network.
> When I try to connect with VNC from my PC (old
> scope) to a new PC (new
> scope) it fails. I've changed my subnet mask to
> 255.255.248.0, but it stills fails. Is there anyway around it?
As long as a machine thinks it is on the old network, all addresses outside
this network are forwarded to the defined gateway. No problem from this
If the gateway is already configured for the new network, bad luck, it just
ignores the call since the message is already on the proper network, no need
to `gateway` the message.
If the gateway is still configured for the old network, it depends on the
routing tables. If the routing tables are still in the old network state,
bad luck, your message goes out to the other networks, but not back to the
network with the double configuration.
Only if the gateway has its network-connection configured for the old
network and has updated routing tables to route messages to the new network
(but not in the old network) back to the old network, then you might get a
Hence, best to do a big-bang update of all machines: proper operating
systems can do that on the fly. Or if you want to do it silently, do it to
an other network addres, not one that includes the old network.