NAT : WAN to LAN, why rewriting source address

NAT : WAN to LAN, why rewriting source address

by Valentin Quelquejay-Leclère -
Number of replies: 4

Hello,

I have a question regarding the behavior of the NAT as described in the previous exams solutions. I don't understand why we need to rewrite the outside source address with the gateway private address for incoming traffic. I tried to look online and in many sources, they describe a behavior where the NAT don't seem to rewrite this address but only the destination address which we obviously need to change. It makes more sense to me. What are the advantages of rewriting this address ? Can it be avoided ? 

Thank you very much !

Best,

Valentin 

In reply to Valentin Quelquejay-Leclère

Re: NAT : WAN to LAN, why rewriting source address

by Ludovic Thomas -

Hi Valentin,

Do you have the question number(s) ?

Ludovic

In reply to Valentin Quelquejay-Leclère

NAT : WAN to LAN, why rewriting source address

by Daniel-Florin Dosaru -
Hi, Ludovic,

One example is in the last year exam, problem 1, exercise 2, c). (First table, at O6) IP source should be 9.8.7.6 or 10.9.1.1 ?

Thanks,
Daniel
In reply to Daniel-Florin Dosaru

Re: NAT : WAN to LAN, why rewriting source address

by Ludovic Thomas -

Thanks,

I agree with you.

In problem 1 of exam 1819, N is a NAT.
As a consequence, in the first table of 2c), we should have D's Ipv4 address as source address. I'm confident enough to assume it's a typo.

However I don't find any issue with exam 1718 because in question 3), X is a web-proxy.

Ludovic