This is our old Q&A Site. Please post any new questions and answers at ask.wireshark.org.

I have what might seem a basic question but I really do not know or can find the answer. The question is; if I have a TCP connection from a server which is from a public IP (Client) to a Private IP (Server)which is through a NAT, is the TCP conversation from Client to Server? Or is it from Client to NAT device, then NAT device to server?

The reason why I ask, if I see retransmissions on the client to NAT device should I also see it from NAT device to server? My thoughts are that the TCP conversation is end to end, from the client to server.

Thanks M

asked 27 Jan '15, 14:11

gmarrun's gravatar image

gmarrun
11113
accept rate: 0%


TCP connections through NAT devices are end-to-end, which means that the client is talking to the server on layer 4. NAT translates IP addresses (layer 3), so they can change, but the TCP connection does not terminate at the NAT gateway. Proxy servers would do that kind of thing, but not NAT gateways.

And yes, you should see the same segments being retransmitted, but since the IP addresses are changed at least partially they can be hard to find.

permanent link

answered 27 Jan '15, 14:18

Jasper's gravatar image

Jasper ♦♦
23.8k551284
accept rate: 18%

Thanks for the quick response and explanation. Greatly Appreciated.

(27 Jan '15, 14:37) gmarrun

You should also verify that only NAT is occurring and not PAT. Most routers perform PAT (Port address translation) in which the IP address and the TCP port numbers are modified when connecting from private to public IP addresses.

permanent link

answered 28 Jan '15, 06:56

Amato_C's gravatar image

Amato_C
1.1k142032
accept rate: 14%

Your answer
toggle preview

Follow this question

By Email:

Once you sign in you will be able to subscribe for any updates here

By RSS:

Answers

Answers and Comments

Markdown Basics

  • *italic* or _italic_
  • **bold** or __bold__
  • link:[text](http://url.com/ "title")
  • image?![alt text](/path/img.jpg "title")
  • numbered list: 1. Foo 2. Bar
  • to add a line break simply add two spaces to where you would like the new line to be.
  • basic HTML tags are also supported

Question tags:

×752
×104
×12

question asked: 27 Jan '15, 14:11

question was seen: 4,909 times

last updated: 28 Jan '15, 06:56

p​o​w​e​r​e​d by O​S​Q​A