Ping another PC on another LAN with different network address?

[Cerdarad]

Hi,

Can I ping another PC on another LAN with a different network address?

Example scenario. A company has a LAN in CityA and another LAN in CityB. A PC in CityA LAN has an address of 192.168.1.5 and a PC in CityB LAN has an IP of 192.168.2.7. Can they ping each other? Would the routers connecting each LAN via a WAN link allow this?

Let's say both have a subnet mask of 255.255.255.0.

Thanks.

[ceh383]

192.168.xxx.xxx was setup as a private, non-routable address set for LAN use. As such, there are probably hundreds, if not thousands of networks setup using the numbers you gave.
As far as know, this is not possible...But, I've been out of this game for a long, long time...

[Cerdarad]

Originally Posted by ceh383

192.168.xxx.xxx was setup as a private, non-routable address set for LAN use. As such, there are probably hundreds, if not thousands of networks setup using the numbers you gave.
As far as know, this is not possible...But, I've been out of this game for a long, long time...

Hi ceh383.

But since it's on a WAN link - I reckon they could communicate. More opinions are welcome though.

[ceh383]

Originally Posted by Megatron

But since it's on a WAN link - I reckon they could communicate. More opinions are welcome though.

Not necessarily, a typical home router will be connected to a WAN on one end, and to a LAN on the other, both being on different networks. As an example: my home network uses 192.168.xxx.xxx while the WAN address of the router is 76.175.xxx.xxx. Any request I make from my computer to a computer outside my LAN will only see the WAN address of my router, with no way of knowing the LAN address it was sent from. This is done through NAT, this is how private LAN's connect to a WAN.

Here is a quote from RFC 1918 that may explain it better...


3. Private Address Space

The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets:
10.0.0.0 - 10.255.255.255 (10/8 prefix)
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)

We will refer to the first block as "24-bit block", the second as "20-bit block", and to the third as "16-bit" block. Note that (in pre-CIDR notation) the first block is nothing but a single class A network number, while the second block is a set of 16 contiguous class B network numbers, and third block is a set of 256 contiguous class C network numbers.

An enterprise that decides to use IP addresses out of the address space defined in this document can do so without any coordination with IANA or an Internet registry. The address space can thus be used by many enterprises. Addresses within this private address space will only be unique within the enterprise, or the set of enterprises which choose to cooperate over this space so they may communicate with each other in their own private internet.

As before, any enterprise that needs globally unique address space is required to obtain such addresses from an Internet registry. An enterprise that requests IP addresses for its external connectivity will never be assigned addresses from the blocks defined above.

In order to use private address space, an enterprise needs to determine which hosts do not need to have network layer connectivity outside the enterprise in the foreseeable future and thus could be classified as private. Such hosts will use the private address space defined above. Private hosts can communicate with all other hosts inside the enterprise, both public and private. However, they cannot have IP connectivity to any host outside of the enterprise. While not having external (outside of the enterprise) IP connectivity private hosts can still have access to external services via mediating gateways (e.g., application layer gateways).

Hope it helps...

[Ned Seagoon]

Originally Posted by Megatron

Can I ping another PC on another LAN with a different network address?

The only way you could do as you suggest is if the local and remote LANs were connected via a VPN that tunnels through the internet.

The usual way of doing this would be via a VPN router at each end. Something like this. Although it is possible to set up a software VPN tunnel like this.

However without employing either of these methods, the answer is as others have suggested, 'No, it is not possible to route private IP addresses across the internet.'

[Cerdarad]

Thanks for the info guys. That's cleared things up.