NAT - Situation when the Outside Local is an RFC 1918 Address

Hi there,

Cisco defines an Outside Local address as:

"The IP address of an outside host as it appears to the inside network. These addresses can be allocated from the RFC 1918 space if desired."

Okay got it. I also know that the Outside Local Address and the Outside Global address are commonly the same.

In what situation would an Outside local address be an RFC 1918 address such as 192.168.2.30?

My guess is, if you for some reason wanted to map 192.168.2.30 to, say, an external mail server at 202.96.54.1

OR a public IP e.g 203.59.40.1 that is translated statically to 192.168.2.30 because there is a web server running on that machine inside the local network

Thanks in advance,

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Comments

SdotLow

NAT: Local and Global Definitions - Cisco Systems

I'm half asleep so I can't bother to read over this right now (I will tomorrow). This will probably have the answer you're looking for. I'm guessing you ran across this with an exsim-max question?

Edit: I think it might be for routing between two parts of an intranet via NAT?

wave

The question was more simple but while I was studying up on NAT terminology again, I was lead down the garden path into more complicated subject matter! ...It could be!

Mierdin

wave wrote: »

The question was more simple but while I was studying up on NAT terminology again, I was lead down the garden path into more complicated subject matter! ...It could be!

FYI - you can and should expect 'more complicated subject matter' whenever dealing with NAT

It is arguably the most difficult concept in ICND1 and ICND2, among other things.

SdotLow is likely right, although you rarely see it used for this purpose in an enterprise for very long, NAT has been used to hide parts of a corporate network's address space. If a company grows through acquisitions, sometimes there's an address space conflict when the two companies merge, so NAT can be used to make it work. Both networks will still run on private address space.