Sooo, this 10 minute discussion of NAT made way more sense then the 1 week discussion of the same topic in my networks course at my university. I'm not sure how I feel about that

To put it a little simpler, imagine your house with 10 devices on the internet (laptops, desktops, game consoles, etc). Those don't have their own external IP address (the one on the internet). You only have 1 for your modem/router, and your router then forwards a packet to each device based on the port # and internal IP address. This is why you need to set up port forwarding if you've ever played an online game, so that when a packet hits your router on a certain port, it knows which computer to send it to

what he explained was overloading, or PAT(port address translation). But it was still a very nice explanation of PAT. just clarifying.

thankyou for uploading more of this guy. he explains things so clearly (as do all the others). going to rewatch them all soon. keep up the awesomeness.

Im starting a degree in Computer Science in a couple of weeks and these videos are getting me really excited for my course - brilliant videos, every single one :)

University of Notingham is awesome. you guys have conversant professors! I also love Nottingham for the fact that Robbin lived there!! Regards from Sri Lanka.

Finally, a rational, clear explanation of how NAT works and how it's implemented. Thanks !!

I would appreciate subtitles. He's talking quite quietly and quickly about complex things.

You guys are my heroes, me who has no computer science background but I am learning how to develop softwares by myself. These videos are extremely helpful. God bless you all

If you want a computer inside your network to accept connections, it must be configured in NAT. This is called “port forwarding” and it instructs NAT that if it gets a connection to (say) port 80, it should direct it to (say) 10.0.0.1:80 in the private network. If there is no such configuration, incoming connections will be dropped. If incoming packet is part of already established connection, NAT just looks at destination port and maintains a state mapping it to ip:port in local network.

nice, keep up the good work computerphile

My favorite KZread Channel. Keep the good stuff going!

There are now also ISPs that use IPv4 NAT instead of upgrading to IPv6, so it could happen that your "external" address of your router is in fact an IP address in a private range. This can severely impact some software, for example games or remote desktop solutions. A colleague of mine had the problem with Teamviewer on one of the German cable networks.

Brady, it would be helpful to have a video focused on NAT or IPv6, or port-forwarding. I've been trying to solve a networking problem: connecting from a remote unix machine (a laptop--meaning I could be anywhere) to a database engine (SQL server) residing on my home network. I've learned more about networking than I ever wanted to know--just in tinkering to get to my database! But now I'm intrigued...

👏👏thx i have that question for so long time, noone had explained me before that the translation not just translate the IP local to global, but also it translate THE PORT number!

What tools did you use for creating this animation? Amazing!

it's also compensated by that mesmerizing animated avatar you have there.

its really nice for this to be explained to be !

this is great, the cissp textbook only explains how ip addresses are translated but never mentioned port number translation.

As a person who had very little computer science knowledge, I found this harder to understand than quantum physics, and I love it.

Thanks for your videos

The first time I ran into a NAT problem I was trying to host a Warcraft 3 map online. Port forwardings at my router didn't work, I had to use something called "port triggering".

I guess the assumption is that the outbound connection happens first and that allows NAT to assign a unique IP:port combination to this specific request and then store it in a table along with the original IP:port pair.

Great video!

Upvoted for the GIF :)

thanks...thank you very much that clears things up a lot

A lot of counties are already using IPv6, though the US has a lot more IPv4 adresses than the rest of us so they keep using it. There's still some things to work out with IPv6 and there's still a lot of companies running old hardware that doesn't have IPv6 enabled which messes things up. Going from IPv4 to IPv6 is a big step and you pretty much need everyone to be able to take it at the same time.

Would you consider doing a vidieo about the transition to ipv6? I would really like to know what the biggest challanges are and why it is taking so long, a lot of devices seem to have some ipv6 functionality already.

My opinion on what MUST appear on this channel is what actually is an algorithm. We had lesson about sorting algorithms, but not on algorithms in general.

i had a lot of trouble with my XBOX because my NAT type was closed. and port forwarding didn't work. after i seen this video i suddenly solft it :o thank you!

UDP doesn't need any special trickery to be address translated. The PAT process isn't looking for sessions, it's looking at source and destination port pairs. Since UDP packets still have a source and destination port, they're translated without issue. Incoming port forwarding is the same.

It works, but not for all protocols, for example, FTP uses two connections - one for control and one for data, the server sends its IP/port over the control connection and the client connects to it (passive mode). Now the FTP server software has to be modified to figure its external IP first. Some routers can rewrite te IP in the packet, but not for all protocols (and not for encrypted connections). However, NAT has other uses than just to save some IP addresses.

Better than most my professors and lecturers

IPv5 wasn't skipped it was given to the Internet Stream Protocol sometime in the late 70's which never saw widespread adoption. So when a new Internet Protocol was being designed it was assigned the next version number - IPv6

We have IPv6 (v5 was skipped?) which allows for as MUCH larger pool of addresses. Many modern OSes and routers support it, but numerous older ones do not and some ISPs appear to be slow in implementing it.

boenrobot is absolutely correct. They'd be using either 192.168.x.x, 172.16.x.x, or 10.x.x.x or there are also ways to reuse the same IP in multiple network segments, but if that is done knowing routing information (especially the router interface used) becomes important

it also gets remapped, but it is a bit more problematic given it is connectionless. UDP-based protocols then have to often go through a bit of extra hassle to figure out the correct port-numbers and similar, but it works...

When I was an IT technician, I used to use 10.100.0.0/16 as my live network and 172.16.0.0/16 as my "something is wrong" troubleshooting addresses. If a trace-route revealed a 172.16.x.x address, then I knew that one of the connections was bad, and with a little cleverness, I could almost always figure out which one it was on the first try. I liked NAT, and was sad when the network finally went to ipv6.

I would love to hear more about how Nat Punch Through actually works.

that requires pretty much an entirely new backbone at every part of the network. ipv6 servers, ipv6 isps, ipv6 routers in people's homes even. old OSes aren't able to make sense of ipv6 either, so it really is a complete overhaul

I know that he meant that? It would still take a while to wright them all and then sync them, I have done it once, and just syncing them took like an hour or something, it's really time consuming. Also, if everyone can upload subs, there would be a lot of stupid onces. Maybe brady can have the ability to make subs and sent them to him, then he can see if they are good and add them.

Great video as always. But, boost up the volume a bit, hardly able to hear.

It is for the same reason that many industries and companies still use XP and haven't moved to Win7, which is because it simply works. Moving to IPv6 would require a huge amount of work an cooperation across the globe, and you can't guarantee that each computer/server/mainframe/workstation is compatible with IPv6.

thanks sir that was so clear

Ah okay, thank you, that makes it a little clearer. I thought it was "if information comes through this port, skip the router and send it directly to computer a/b/c" Even when im the only pc on a network i've had to set up portforwarding though. :)

With the arrival of IP6, (and lets laugh at the thought that the world all moves over to it eventually), would this be the end of NAT/PAT's needed? Is there an advantage/disadvantage to each home PC having a unique IP address and not a private internal one? I as this as a Small Company / Home user point of view.

can you please amplify the voice data? hardly able to hear.

First of all, 65536. Second of all, you need to remove some edge cases like 128.243.0.0 or 128.243.255.255 so it's actually a bit less then that. But third of all, the way you design network is by dividing it into sub-networks. So for instance, department of Mathematics may get 128.243.0-15.*, department of Computer Science may get 128.243.32-63.*, and so on. In those cases, some departments may run out of addresses even though there are addresses available in different sub-networks.

7:06 I run a server behind a router. I've had to deal with all of these problems at one point or another. It's really annoying when my router is all like "CHANGE PLACES!!" and remaps all the private addresses.

IPv6 is superior to v4 in almost every way. The transition will occur naturally as older devices are replaced and it becomes more cost effective to implement IPv6 and cover any gaps with dual stacks.

Port forwarding. Now I understand you :)))

Those terms are somewhat ambiguous, and different games will have different meaning for them. Generally with open NAT the game is able to request your router to forward an incoming port to the game, you effectively become a server. Strict means it was unable to do so. Moderate may mean it was able to "punch through" your firewall using a variety of tricks (UDP, not TCP), but such solutions may be sub-optimal or flakey.

while IPv6 is probably the eventual solution, I have wondered sometimes if an IP-suffix system could have also worked (as a compromise). basically, packets would daisy-chain 2 IP headers, with the first having the global IP and the second a local IP. ex: 243.119.24.31-10.0.169.173:6942. this would then effectively give a 64-bit address space, while still being routable over IPv4. then things are fudged in the network stacks to make it all work... also, sort of like an inverted VPN...

Portforward in a nutshell: Behind your router you have computer A, B, C, D, and E. All 5 of those computers are behind one single public IP address. When a computer somewhere else on the internet connects to your IP, it doesn't know which of your 5 computers to connect to. Portforward makes your router say "If it's this type of request, send it to computer B, if it's that type of request, send it to computer D"

It might be just me, but i would love to see a video about port forwarding, having had to do it for several different games/programs, i still don't understand what it does exactly.

See 802.3 ethernet frame structure. Both source and destination MAC are packaged near the start of the frame.

Moving to IPV6 is a tremendous challenge because a lot of older routers/network devices don't support IPV6. TO suddenly mandate everyone use it would be a disaster. NAT is basically extending ipv4 capacity, the same a hotel extends it's phone network capacity by giving every room an extension number rather than an actual phone line.

There are a lot of backbone switches controlled by ISPs and second tier providers that are incredibly expensive and do not support IPv6. The transition will take a long time.

yes and no. yes: in that ports are mapped and translated directly via the router (it doesn't need to care what they contain). no: in that the higher-level (application) protocols often need to be more aware what the public IP and ports are in order to work correctly, so sometimes the protocol needs some mechanism to figure this out (usually during a "handshake" process or similar). OTOH, with TCP, more of the details are often abstracted over, so it is less often an issue.

this guy gave me a lecture at the Uni

Except for the fact that IPv6 has the capability of having a unique address for every cubic centimetre of the planet. We won't need a replacement until we become an interstellar civilization.

Can you make a video explaning the difference between a router, switch and a hub?

So how does NAT come into play when you're playing games online and it tells you that you have either strict, moderate or open NAT?

for most home routers the ip is 192.168.1.254, some of you guys at home type that into your address bar and press enter you will be directed to your home router

Because Sean likes people asking that on every video.

I get the outgoing translation, but how does the incoming translation process work? I don't get how the hub knows to which local IP to send the data to if there's no indication where it is coming from. Especially since you're limited to the amount of ports.

What effect does the NAT type have, Type 2 for example, or Strict, moderate and open.

Good one

A single computer doesn't need a router, but you still need a modem. Most ISPs now give you a modem/router combo anyway though.

If it came from public Internet, it means that your hosting providers routers are misconfigured. Packets whose source or destination address falls within a private address space, must be dropped by the router that connects private network to public Internet. It's far more likely, that the packet did originate from within the hosting site's network.

because the NAT makes it hard to discover a private address does this add a layer of security?

How about raising the level on computerphile? i guess numberphile and the other channels have pretty clever and complex questions when this is beginner stuff.

it would make home networks much less of a hassle, i have had a lot of nat related problems. I also can't imagine ISPs being completely fine with having to implement layers upon layers of nat of ther own.

Something he did not explain very well is that the relabeling is only done in the Source port when the packet is going out and that when it packet arrives back, that "fake relabled port" is now on the destination port. The reason being google (for instance) still needs to know that the packet is going to port 80, receiving "18" would not work as the packet would be rejected.

Do I need a router in my house if I only have one device using the internet connection?

I take a break from work to... go back to work. :-) Do you mind if I throw in some questions frame tunnelling? I'm a bit stuck on VXLAN at the moment. :-)

NAT dose give you a layer of security because any unsolicited incoming packet gets blocked simply because the router doesn't know what to do with it.

So next up is port forwarding?

When will you talk about CARP?

That privacy benefit sounds a bit weird, aren't there things like tor for that?

I guess NAT gained the upper hand over the introduction of ipv6 because it can be implemented on one party without the other noticing it?

So, that problem at the end is solved by port mapping on my router, right?

MAC addresses are not sent over the internet. The source and destinaion MAC address inside a packet is changed whenever the packet passes a networking device. This way the devices have an idea on how the packet can return to it's destination, only the source and destantion IP addresses stay the same throughout the entire "journey". So the MAC of your PC can never be used to locate you, it is simply never transmitted.

Can you do a video on network DMZ's?

OMG IT ALL MAKES SENSE

Can you please make a video on CIDR Notation!

Oh so that's what NAT stands for when i do my port mapping?

'cause this is not Numberphile. Brady already adressed that.

That address space supports 65536 addresses and at most 65534 host addresses.

But, this will only hold out for so long. IPv6 has many benefits over IPv4, besides more addresses.

nope, it just did many years ago, and if you haven´t changed yours since then, you can still have GIFs as avatar

Because it's not Nubmerphile. It's Computerphile, they use old perforated printer paper, which is appropriate.

The router still assumes that there are multiple computers, cause normally you wouldn't use a router for just one connection. (Also if you have a cell phone, game console, or any other internet-enabled device, it's going through your router too)

Every single computer in the world needs upgrading by 2038. Computers need to all be 64bit by then, because of the way time works. The upgrades will come.

Well, that's all very nice

The website I maintain at work has had visits from a 10.*.*.* address - I contacted the hosting provider of our server and they say the connection didn't come from their network - so this private IP address must have been used on the public internet, and I was unable to track down where it came from. I assume this must be because of NAT? It's really a problem when tracking down suspicious behaviour.

how do i switch my strict nat type to open?... my ps4 says that my router has a nat type of 2 but when i go to play games it says my ant type is strict and i cant connect to my friends.. i dont get it...

Computerphile uses this kind of paper instead of the regular numberphile brown paper so as to differentiate itself

so we basically need to make IPV5 so that we will have several times the capacity, we just need to make the move, we have to upgrade computers soon enough anyways because the internal clocks are counting down

You should've explained Class A/B/C Networks for that matter, but I haven't watched all the video yet, so you might have, but I haven't watched it yet.