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Daft question - connect two different networks

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  • Daft question - connect two different networks

    Please be gentle with me

    I know class based networks are thing of a past but if you have one network on say 10.0.0.1/24 and another on 192.168.1.1/24 how is it possible to let them talk to each other. Our servers use 192 etc and clients are on 10.0 etc

    I'm assuming some routing has take place, as naturally they wouldn't talk to each other would they? I'm having trouble understanding how or where they are able to route between

    Or does CIDR allow for this ?

    Thanks
    Last edited by Ghostrocket; 17th February 2017, 17:37.

  • #2
    The class of the network vs CIDR notations doesn't really come into it. Regardless of how the address spaces are defined, if they're not the same address space, you have to route between them for the devices on either network to talk to the other network. The /24 notation is the CIDR way of defining the network 'width', and that simply means how many host addresses are available to be used on that network. The other way of writing that specific notation is '255.255.255.0'. Both are ways of representing what's called the 'network mask'. If you are using both of those address ranges in your system, and you're not having any problems, then something is routing between them. The routing could be done inside your firewall/proxy device, in a dedicated router, a server configured as a router (multiple network cards a must!) or in a switch, if it is considered a 'Layer-3' device (refers to one of the 7 layers of the OSI TCP/IP stack protocol model).

    A computer knows whether another network address is in the same address space as itself, based on it's own network IP and mask. When a packet is sent to another address, if that address is in the same space, the packet is sent directly to the address. If that address is outside the space of the sending device, the sender points the packet at the default gateway of it's own address space. The default gateway (router) receives the packet and either A) relays on to the other network directly if known, B) forwards on to another router that should be better-suited to handle that packet, or C) drops the packet because it has no idea what to do with it.

    So look at the config on any PC on any subnet, specifically the 'Default Gateway' value. That IP address is the router for that subnet. Whichever device holds that IP is doing your routing.
    *RicklesP*
    MSCA (2003/XP), Security+, CCNA

    ** Remember: credit where credit is due, and reputation points as appropriate **

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    • #3
      Thanks Rickles for restoring my sanity

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