[X-Newbies] IP addresses

[Raoul Armfield]

Chris Walker wrote:
> On 15/6/05 Raoul Armfield wrote: 
> 
> 
>>It really depends on what x.x is equal to.  For instance if x.x is equal 
>> to 10.0. then yes both 0.5 and 1.11 are on the same subnet.  
> 
> Well that solves one thing.  I always thought that say 192.168.1.10 and
> 192.168.0.10 would be on different subnets, the 0 and 1 (third number)
> being the determinants.  

you are right in this case but note that it is dependent on what the 
first set of numbers is.

Here is a little chart that will help out

     * Class A = 1.0.0.0 to 126.0.0.0
     * Class B = 128.0.0.0 to 191.255.0.0
     * Class C = 192.0.1.0 to 223.255.255.0

This will help you determine if you are on the same subnet or not. 
Again assuming the subnet mask is 255.x, 255.255.x or 255.255.255.x


> 
> Lets take this a stage further.  At the moment I can use a VPN  to log in
> to the Uni servers.  Suppose I want to do a remote login to my own
> machine using IPSecuritas or VPNTracker (the Uni's preferred method).  We
> will suppose my machine is at LAN 10.0.0.2.  In order to get a connection
> this would mean the remote machine would need to be on a completely
> different subnet say 192.168.x.x (or 172.16.x.x) rather than 10.0.1.2/3
> whatever.  I'm ignoring public IPs which will obviously be different -
> we'll assume they are both fixed for arguments sake.
> 

Theoretically you could have a internal address of 10.0.0.2 at the Uni 
and a internal address of 10.0.0.2 at home and still be able to VPN in 
because as far as the VPN concentrator is concerned the originating IP 
is whatever your external ip address is and that once your VPN 
connection has been authenticated you will get an internal IP address 
that is different from what your router at home assigned to your NIC. 
because now you have a virtual NIC.

I probably butchered the explanation also bear in mind that I am 
thinking about Cisco VPN client not VPNTracker so I may have left out 
some elements but this is how I understand it.  I am sure someone more 
knowledgeable about VPNs will correct me or clarify everything.



> Is this correct?
> 
> cheers,
> 
> Chris
> 
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-- 
Raoul