Dynamic NAT - Network Address Translation

[@PracticalNetworking]

👉 *Want more?* Watch the rest of the NAT Series: kzbin.info/aero/PLIFyRwBY_4bQ7tJvbLA9A0v8Fq9l-H923 🐦 *Enjoy this content?* Help me out with a like and/or Retweet: twitter.com/ed_pracnet/status/1513944439625977858 📌 *Want to learn Subnetting?* --> kzbin.info/aero/PLIFyRwBY_4bQUE4IB5c4VPRyDoLgOdExE 🖧 *Want to learn Computer Networking?* --> kzbin.info/www/bejne/mJuQipmXoM-fosU

[@sds.gaming738]

DearSir, I have a question regarding the example you mentioned for FTP.You explained how DNAT can be a bidirectional while being active. My question is Can't that be the case in DPAT as well? Because if the connection is active,the port translated by the DPAT will remain the same, and the server can see the translated port and initiate a data channel. Kindly clear my confusion. And I have been following you for the last couple of weeks(found you anonymously).I love your content, the way you explain every tiny detail is amazing.I wish you were available to me in my university. Thanks a lot for such amazing content ❤

[@rotrose7531]

Your channel provides the best, most easy to understand networking content to all of us. I can not say enough thanks.

[@PracticalNetworking]

Thanks again for the kind words =)

[@moonlightknight6877]

Thank you for creating such amazing videos. Your videos have been a lifesaver for me. I was not understanding NAT vs PAT until I watched this series.

[@VideosfromElle]

Just such a great, consistent, valuable delivery!

[@PracticalNetworking]

Thank you, Elle. Glad you're enjoying these =)

[@justsomebody14]

Thanks so much for your work! It helps me so much! You're the best channel on network topic i ever saw!

[@PracticalNetworking]

[@Demopanz]

Terrific video to help explain what i am reading in my network+ book. Thanks for having this sort of stuff easily available

[@simonsays5569]

Waiting for the complete networking course !! Great content as always !

[@PracticalNetworking]

Thanks SImon!

[@shujauttali2608]

This feels like an offline class 👍👍👍

[@justsurajp]

@8:15 Isn't the Lazy "Static NAT" also possible if the Number of hosts is less than the number of IP addresses in translation?

[@PracticalNetworking]

Sure. Yes. But you're then wasting public IPs. But yea, I guess you can still use it.

[@neill9819]

9:30 you said that one of the disadvantages of dynamic NAT is non deterministic IP assignments which can cause a problem when trying to configure an ACL. Isn't the configuration of an ACL based on private IP addresses and not on public ones?

[@skalmelid]

In your ftp example. At 5:47 when opening the second channel, did you actually mean a different random port than the control channel is using? You called them both R.

[@PracticalNetworking]

Great Q. Yes, different random port.

[@justsurajp]

Isn't there also another major fundamental flaw in this approach that the external systems always can not rely on 1 IP for 1 machine? i.e., if @2:55, IP 54.5.4.1 was assigned to 10.7.7.71 and this information was for some reason saved by the external host, when the system changes to state @4:05, the data held by the external host is no longer correct. If at all the host sends a packet back when the system is at the latter state, it would reach the machine 10.7.7.74 instead of 10.7.7.71. Is this understanding correct?

[@justsurajp]

Of course, the single packet sent back when the system changes to the latter state will not be accepted because there is no active session. But just considering a hypothetical case where the connection still somehow existed but the entry in the router table did not.

[@justsurajp]

ah okay, just reached the "disadvantages" section of the video. Answers my question. :)

[@FossWolf]

Great content 👍

[@nickjurkovic6831]

Amazing, this is actually fun to watch :)

[@fuzzyball2132]

Great content and effort!!!

[@PracticalNetworking]

Thank you =)

[@asish4ever]

Nice session, thank you

[@aaronnikels5706]

Hi, thanks for the fantastic content! I have a question about FTP I was hoping you could answer... Why does FTP initiate a new connection over port 20? Why not just respond with the data over port 21? Why make this entirely new connection if you can just use the same channel? Also, even if FTP uses port 21 anyways, why not address the packet to the same temporary port that the request was received from? If Active FTP cannot work with dynamic PAT, then that means it is attempting to send data to a new port on the local host, otherwise if it was sent to the same port that initiated the connection on the router's public IP, the router should be able to locate the entry on its routing table and translate it. Why not just use the same port that the request was sent from over port 21 on the control channel? I know Active FTP is legacy, but it sounded like passive FTP had the client initiating both connections, and I just don't see why the server couldn't just respond with the data either over the same port or just send the data from a different port (i.e. port 20) to the same port the client requested it from, that way the client wouldn't be initiating new connections and it would just be a lot more consistent Either way, great video! Your explanations are always very clear and easy to understand

[@PracticalNetworking]

Glad you enjoyed them. FTP was created before NAT took over the world, so the "flaw" of Active FTP not working through Dynamic PAT was less relevant. As for why not use the same channel, remember bandwidth was very limited back then. The idea of a separate "data" channel was you could use the control channel to start a download for three files, and it would create three separate data channels for the actual data transfer. This way your "control" channel wasn't stuck waiting on the file to finish transferring before you could send more "control" commands (requests/uploads/etc). Hope that answers your question. If not, feel free to continue the discussion on Discord: pracnet.net/discord Otherwise ... Could you do me a favor? Do you mind sharing this video on Linked In, Reddit, Twitter, Facebook, or any other social media you use? As an independent creator, that would be an _enormous_ help, and I would appreciate it _greatly_ .

[@aaronnikels5706]

@@PracticalNetworking Sure thing. Also, I've already recommended your channel to a few of my friends. I think your packet traveling video is the best!

[@PracticalNetworking]

@@aaronnikels5706 Thank you, Aaron. I appreciate your support. PS, there was a question on my discord related to this and FTP's control vs data channel... was that you? If not, you might enjoy skimming the Q & A.

[@fajarhariadi4291]

how can the router have multiple public ip address? do each ip have their own port and cable to the public, or using sub-interface? and did they need to be in the same subnet, or it can be done with different subnet of public ip address?

[@PracticalNetworking]

Routers can be assigned multiple addresses from either the Interface subnet or another subnet. If it's another Subnet, a route will have to be added on the upstream router. Some details here: www.practicalnetworking.net/series/arp/proxy-arp/

[@fajarhariadi4291]

@@PracticalNetworking thank you very much, this is help me so much to understand much more in networking

[@MegaZeks]

Sorry I still dont' understand it. I thought only 1 public IP address is provided by ISP per router. That is why from every device from local network that is connected to the router, when I type in browser "what is my IP" I get the same public IP. How can there be more of them per 1 router?

[@johnnydepp2090]

Have a complete networking course please

[@PracticalNetworking]

Hi Johnny. Loved you in Pirates of the Caribbean! ;) I published some Networking videos here: kzbin.info/aero/PLIFyRwBY_4bRLmKfP1KnZA6rZbRHtxmXi

[@jnyfah]

I enjoyed this

[@PracticalNetworking]

Glad to hear =).

[@ratnahnavar5717]

Superb

[@PracticalNetworking]

Thanks 🤗

[@IliyaDamyanov]

Nice video.

[@rafay1708]

Thanks 👍

[@PracticalNetworking]

You're welcome, Rafay!

[@subee128]

thanks