NAT inside local/outside local inside global/outside global question.

mitchtin · April 2016

Hi Guys,

This really annoys me because i know it is a simple concept but I just can't memorize it. Are the below correct definitions? and do people have any specific ways that they memorize the definition of each term.

inside local - name of inside source address before translation

outside local - name of destination host before translation

inside global - name of inside host after translation

outside global - name of outside destination host after translation

Thanks

pinkiaiii · April 2016

think your correct but,then again id would depend on nat,since say you have switch with networks and that switch is connected to internal router that is connected to isp - in this case you would have theoretically two inside local addresses,but the one you would use would be the router that is connecting local networks and interface that goes to ISP as your inside local ? correct me if wrong.

Then theres situations where if doing labs -two people defying addresses on two networks would use same inside local/outside local and both would be sort of looking at each other ends as outside global/inside global.Not sure really if its correct concept but its the way i see it.

anyways heres explanation from cisco:

[h=2]Term Definitions[/h] Cisco defines these terms as:

Inside local address—The IP address assigned to a host on the inside network. This is the address configured as a parameter of the computer OS or received via dynamic address allocation protocols such as DHCP. The address is likely not a legitimate IP address assigned by the Network Information Center (NIC) or service provider.
Inside global address—A legitimate IP address assigned by the NIC or service provider that represents one or more inside local IP addresses to the outside world.
Outside local address—The IP address of an outside host as it appears to the inside network. Not necessarily a legitimate address, it is allocated from an address space routable on the inside.
Outside global address—The IP address assigned to a host on the outside network by the host owner. The address is allocated from a globally routable address or network space.

These definitions still leave a lot to be interpreted. For this example, this document redefines these terms by first defining local address and global address. Keep in mind that the terms inside and outside are NAT definitions. Interfaces on a NAT router are defined as inside or outside with the NAT configuration commands, ip nat inside destination and ip nat outside source . Networks to which these interfaces connect can then be thought of as inside networks or outside networks, respectively.

Local address—A local address is any address that appears on the inside portion of the network.
Global address—A global address is any address that appears on the outside portion of the network.

mitchtin · April 2016

thanks, i think from the cisco definitions I have made my own way of remembering. I think we just need to remember that 'local' and 'global' refer the locations of the address I.E:

Local = inside the network

Global = outside the network

james43026 · April 2016

mitchtin wrote: »

thanks, i think from the cisco definitions I have made my own way of remembering. I think we just need to remember that 'local' and 'global' refer the locations of the address I.E:

Local = inside the network

Global = outside the network

This is correct. You can also break it down like this.

Inside local = IP address of an inside node, before NAT translation, and is the IP address of the node as seen by devices inside your network.

Inside Global = IP address of an inside node, after NAT translation, and is the IP address of the node as seen by devices outside your network

Outside global = IP address of an outside node, before NAT translation, and is the IP address of the node as seen by devices outside your network, usually a public IP address

Outside Local = IP address of an outside node, after NAT translation, and is the IP address of the node as seen by devices inside your network

NAT inside local/outside local inside global/outside global question.

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