NAT IP addresses

[Neven1986]

Hello community,

I would like to get some explanation regarding IP Addresses "types" in NAT.

Recently I saw empty template (basically Excel sheet) for NAT Translation rules in which are 4 columns regarding IP addresses.

Original source IP - that is IP of Host for example (172.18.0.20)

NAT Source IP - ???????

NAT Destination IP - ???????

Destination IP - that can be some IP address to which we are translating internal (Original source IP) address. 193.34.34.34

What I'm puzzled with... What does someone mean with NAT Source/Destination IP. What is that? Do somebody has Explanation for them?

Thank you,

Neven

[RicardoReynaud]

Hi Neven,

Can you put the command you are trying to use?

Source IP can be used on an access-list to only allow certain IPs or ranges to NAT outside to the outside, for example.

Just write the command and we can go from there!

Thanks,
Ricardo

[Neven1986]

Hi Ricardo,

that is the Problem, so to say... I'm not responsible for that part of Network, but they want me to fill this form. I've asked them via E-Mail what does this mean, but no reply came yet.

I would like to know if somebody is aquinted with that terminology? And now I'm personally into finding out what this means, as well.

Thank you,

Neven

[RicardoReynaud · Accepted solution]

Hi Neven,

It seems they are talking about:

http://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/4606-8.html

• 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.

The four types would match yours, no?

Thanks,

Ricardo

[Neven1986]

Thank you Ricardo.

This would probably be it. I was puzzled, because as "end user" I don't need to know all this informations, neither they need to have them all for just NATting. Maybe I'm wrong, but I've so far I've never used this many IPs to configure NAT. 

Maybe they need them as well for some other things, like firewall opening. 

Don't know.

But thank you, this would probably be it...

BR,

Neven

[Martin Carr]

The source is address is where the traffic is sourced from.

The destination address is what you want the source translated to.

For you to access the Internet for example, NAT translates your private address to your public one.

Martin