Can't access computer on different subnets

  • Thread starter Thread starter Jp Armstrong
  • Start date Start date
J

Jp Armstrong

Hello everyone,

I'm here at work trying to solve this problem and i just can't find the
solution on the internet. I service around 70 or so computers in a
department at a university. Some of they're IP addresses are ...
143.93.38.* and others on 143.93.40.* ... Now my new boss is planning
on upgrading some of the machines but first wants to make a back-up of
everyones local profile. I'm able to access a computers c-drive
(\\computer\c$) so long as the subnet is the same.

Ex: I can access from computer A (143.93.38.11), computer B
(143.93.38.52) but not computer C (143.93.40.14)

now i've tested them on different machines. As long as the subnet is
the same they can access each other.

The previous network adminstrator had set up those machines with the
143.93.40.* subnet with firewalls turned off. Which is a big no no.

keep in mind we are on a domain not workgroup and we run our own domain
controller.

Any help will be much appreciated,
Jp Armstrong <[email protected]>
 
I'm assuming you're using a "class c" subnet, in which case you won't be able
to access one range from the other - that's by design.

There are two ways round this - Make the network class B (mask=255.255.0.0)
or else set-up one computer to act as a router between the two subnets.

Incidentally, I take it you work for Fachhochschule Trier? According to
RIPE, that's who this range belongs to. If so it seems you own the whole
range from 32.0 to 63.255, so any subnetting is an internal voluntary choice.
There may be reasons for splitting the range up, so changing the mask may not
be an appropriate action. Best seek advice on this.
 
the IP's I gave you are for demonstration they aren't the real ones.

The university as a whole owns a certain class B range, i dont what the
number is.

The odd part of it all is, it works if the firewall off. My best guess
is that I can flip a switch in the registry to allow me to access
shared drives over class C subnets.

Thanks Ian but i dont think i can have a router between the two subnets.
 
Not sure what firewalls you are talking about since I took your first post
to mean that the prior administrator turned them off. But a common setting
available in both the XP and 3rd party firewalls can restrict the scope for
file and printer sharing to machines on the sharing machine's local subnet.

Doug Sherman
MCSE, MCSA, MCP+I, MVP
 
Just to clarify here, the way TCP/IP works, machines cannot communicate with
each other directly if they are in different subnets. That is by design. Thus
if your mask is 255.255.255.0 then they cannot communicate. If the mask is
255.255.0.0 then by rights they should be able to.

HST I've seen some cases where a fault seems to exist in the TCP/IP stack,
in that computers with differing third octets cannot communicate regardless
of the mask. (and even with 10-series addresses, so it's not a case of
classful addressing) I think this might be down to a bug in some NIC
drivers. W2000 too, so wasn't a firewall issue.


BTW, when I say a router I don't mean anything costly like a Cisco, I just
mean any computer set to relay packets between the two physical segments. If
you just need a temporary setup this might be the easiest workaround.
 
I just turned the firewall off on that machine on the different subnet
and its able to communicate with my machine, by going to ...
\\computer\c$ . The file and sharing exception is checked when the
firewall is on. We are using the windows firewall.

I have to say im scratching my head on this problem.
 
problem resolved..

go to:

windows firewall > exceptions > double-click "File and Print Sharing"
and change the scope for each port. Then restart the firewall service.

Thanks doug, when you said "firewalls can restrict the scope" i tried
to find something like that on the firewall settings.

Thank you also Ian.
 
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