Two machines having the same IP address?

[whiteGloveReview]

Hi there, 

 

So, I have a server machine running Ubuntu and a laptop on the same local network and when I look up my public ip address on these machines, they both end up with the same ip.

They're on the same subnet on my local network and they both have different local addresses. my laptop ends in 188 and the other ends in 252.

 

I wonder if this is just a bug or an oversight of mine because I know that no two computers should have the same ip or they'd both get the same traffic, but i've run these checks a couple times now over the span of a good week now and with the same result. Keep in mind that I am, most of the time connected with the server through SSH, and, though I know this shouldn't cause interference like this, it's not, a VPN or anything to that effect, so it shouldn't interfere. 

 

I'm just putting this out there to see if i can get any explanations for this.

[Skiiwee29]

If you are behind a router, then no. You will have a feature on your router called NAT, or network address translation. Basically it takes your 192.168.X.X and will translate it to your public IP address that is assigned by your ISP. The outside world will see this IP as belonging to your Router, not the equipment attached behind it. 

[whiteGloveReview]

Just now, legacy99 said:

If you are behind a router, then no. You will have a feature on your router called NAT, or network address translation. Basically it takes your 192.168.X.X and will translate it to your public IP address that is assigned by your ISP. The outside world will see this IP as belonging to your Router, not the equipment attached behind it. 

But i should still have two different ips though, right? they shouldn't be the same.

[Skiiwee29]

4 minutes ago, whiteGloveReview said:

But i should still have two different ips though, right? they shouldn't be the same.

On your LAN you will different IPs, but when you look it up. You have a single IP from your ISP that all traffic is sent to and from according to the WWW. They dont see your devices behind your router. All they see is your router. Once you send it, your router knows what device it came from and where the traffic should end up ultimately when sent back to you. All say linustechtips.com is going to see is your IP, say 208.87.201.8 and your Router mac address of 0000.0001.1234 and be like on, here is what you want. Once your router receives that, its like on, device at ip 192.168.0.5 requested this information and forwards it to your device. 

 

So technically each device behind the router is not seen by the world so it does not have a public IP address, only your router does. 

[Aleks NE]

6 minutes ago, whiteGloveReview said:

Hi there, 

 

So, I have a server machine running Ubuntu and a laptop on the same local network and when I look up my public ip address on these machines, they both end up with the same ip.

They're on the same subnet on my local network and they both have different local addresses. my laptop ends in 188 and the other ends in 252.

 

I wonder if this is just a bug or an oversight of mine because I know that no two computers should have the same ip or they'd both get the same traffic, but i've run these checks a couple times now over the span of a good week now and with the same result. Keep in mind that I am, most of the time connected with the server through SSH, and, though I know this shouldn't cause interference like this, it's not, a VPN or anything to that effect, so it shouldn't interfere. 

 

I'm just putting this out there to see if i can get any explanations for this.

 

This isn't normal in my experience , all your device have the same Internet Protocol, however the is another one I don't know the correct name for it I just call it internal internet protocol, so you should have your main  IP:  109.135.28.58  and the other IP'S like: 192.168.1.1 and the next device would be 192.168.1.2 at least that's how mine are. Try resetting your router or changing your ip in your settings.

[whiteGloveReview]

Just now, legacy99 said:

On your LAN you will different IPs, but when you look it up. You have a single IP from your ISP that all traffic is sent to and from according to the WWW. They dont see your devices behind your router. All they see is your router. Once you send it, your router knows what device it came from and where the traffic should end up ultimately when sent back to you. All say linustechtips.com is going to see is your IP, say 208.87.201.8 and your Router mac address of 0000.0001.1234 and be like on, here is what you want. Once your router receives that, its like on, device at ip 192.168.0.5 requested this information and forwards it to your device. 

once again, i'm reminded on how fantastically complicated networking can be. thanks a bunch.

So to fix this, could I just call my ISP up and request that my IPs be changed?

[Skiiwee29]

4 minutes ago, whiteGloveReview said:

once again, i'm reminded on how fantastically complicated networking can be. thanks a bunch.

So to fix this, could I just call my ISP up and request that my IPs be changed?

No, there is no issue with this. This is how NAT works. If you are experiencing no issues with your internet traffic etc... then the old saying goes...

 

If its not broke, why fix it? IE: Nothing is broke here and working exactly as intended. 

[MimigaKing]

30 minutes ago, whiteGloveReview said:

Hi there, 

 

So, I have a server machine running Ubuntu and a laptop on the same local network and when I look up my public ip address on these machines, they both end up with the same ip.

They're on the same subnet on my local network and they both have different local addresses. my laptop ends in 188 and the other ends in 252.

 

I wonder if this is just a bug or an oversight of mine because I know that no two computers should have the same ip or they'd both get the same traffic, but i've run these checks a couple times now over the span of a good week now and with the same result. Keep in mind that I am, most of the time connected with the server through SSH, and, though I know this shouldn't cause interference like this, it's not, a VPN or anything to that effect, so it shouldn't interfere. 

 

I'm just putting this out there to see if i can get any explanations for this.

You said it yourself. There are two kind of IPs. Public and Private. 

 

Public IP is the one your network is known as on the internet. 

Private IP is those in your local private network. In your case, ending in 188 and 252.

 

You have no control over the public IP and will be the same whatever device you use to check it. As long as you are on this connection. 

Your private IP can be changed by you through your router. 

[whiteGloveReview]

31 minutes ago, legacy99 said:

No, there is no issue with this. This is how NAT works. If you are experiencing no issues with your internet traffic etc... then the old saying goes...

 

If its not broke, why fix it? IE: Nothing is broke here and working exactly as intended. 

I know there's something wrong somewhere along the line. it's proving to be difficult to access the servers webpages from the laptop (a good example is plex. I just installed it, and I'm to log onto the webpage (http://192.168.0.252:32400/web) to set it up and I wind up at an error "ERR_CONNECTION_TIMED_OUT") 

[MrKickkiller]

1 minute ago, whiteGloveReview said:

I know there's something wrong somewhere along the line. it's proving to be difficult to access the servers webpages from the laptop (a good example is plex. I just installed it, and I'm to log onto the webpage (http://192.168.0.252:32400/web) to set it up and I wind up at an error "ERR_CONNECTION_TIMED_OUT") 

 

35 minutes ago, legacy99 said:

No, there is no issue with this. This is how NAT works. If you are experiencing no issues with your internet traffic etc... then the old saying goes...

 

If its not broke, why fix it? IE: Nothing is broke here and working exactly as intended. 

 

43 minutes ago, <Aleks> said:

This isn't normal in my experience , all your device have the same Internet Protocol, however the is another one I don't know the correct name for it I just call it internal internet protocol, so you should have your main  IP:  109.135.28.58  and the other IP'S like: 192.168.1.1 and the next device would be 192.168.1.2 at least that's how mine are. Try resetting your router or changing your ip in your settings.

 

http://imgur.com/a/7t3qT

Just a selection of slides from my university professor that explains NAT pretty well.

 

[Skiiwee29]

6 minutes ago, whiteGloveReview said:

I know there's something wrong somewhere along the line. it's proving to be difficult to access the servers webpages from the laptop (a good example is plex. I just installed it, and I'm to log onto the webpage (http://192.168.0.252:32400/web) to set it up and I wind up at an error "ERR_CONNECTION_TIMED_OUT") 

Well thats an internal IP address, not external, so its going to have nothing to do with your external IP. This will likely be more a configuration error in either the server or your router. 

[Skiiwee29]

1 minute ago, MrKickkiller said:

 

 

 

http://imgur.com/a/7t3qT

Just a selection of slides from my university professor that explains NAT pretty well.

 

Yep, I  understand and know exactly how NAT works... I am a network engineer for several ISPs. 

[jj9987]

Due to lack of IPv4 addresses, NPAT (combination of Network Address Translation and Port Address Translation) is used, as it was already mentioned. Network Address Translation is used to assign public IP to private IP, whereas Port Address Translation will assign a certain port to certain IP.

 

In real life, this means that you have 1 public IP (external network), but you have a local network (also known as internal network), that has it's own addressing (10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16). All the devices will connect to the internet via that one public IP (that does not belong to the private addresses listed before) but through different ports. All the replies will also come to that same port and then the router will know, to which computer the packet should be sent to.

 

To visualize: Let's say you have public IP 11.22.33.44 and local network of 192.168.0.0/24 (so router has 192.168.0.1 and devices have from .0.2 to .254). Device1 has local network IP of 192.168.0.2, public IP 11.22.33.44. When it connects to the internet, a random port above 1000 or so (not fully sure about this) is chosen, so it connects to the service with 11.22.33.44:43451. Device2 will have for example 11.22.33.44:55132 etc.

 

This does not apply on IPv6 addresses, because NAT is not used there (can be used, but highly recommended to avoid). There are a lot of IPv6 addresses, not even close to running out of them anytime soon and therefor every device will have it's own public IP address, that you can use.

 

In conclusion, yes, two devices can have same public IP addresses if they are in the same local network. But they can not have same private IP addresses, if they are in the same network. 

 

You can set up port forwarding in the router to direct all traffic, that reaches specific port on the public IP, to go to specific local network IP.

 

EDIT: slightly improved.

[MrKickkiller]

6 minutes ago, whiteGloveReview said:

I know there's something wrong somewhere along the line. it's proving to be difficult to access the servers webpages from the laptop (a good example is plex. I just installed it, and I'm to log onto the webpage (http://192.168.0.252:32400/web) to set it up and I wind up at an error "ERR_CONNECTION_TIMED_OUT") 

So you installed Plex on the 252 machine, right?

A. Are you sure plex is running on 32400. If unsure try running a portscan on the pc you installed Plex on. A good tool for that is Nmap.

B. I assume the laptop is running on wifi. Check if the wifi is on the same subnet as your Plex machine. IE: 192.168.X.Y. X should be the same, Y can be different.

[MrKickkiller]

1 minute ago, legacy99 said:

Yep, I  understand and know exactly how NAT works... I am a network engineer for several ISPs. 

Quoted you to notify you that I had posted some (perhaps) helpfull imagery. From your previous comments I immediately saw you were quite knowledged in networking  

[whiteGloveReview]

52 minutes ago, MrKickkiller said:

So you installed Plex on the 252 machine, right?

A. Are you sure plex is running on 32400. If unsure try running a portscan on the pc you installed Plex on. A good tool for that is Nmap.

B. I assume the laptop is running on wifi. Check if the wifi is on the same subnet as your Plex machine. IE: 192.168.X.Y. X should be the same, Y can be different.

the first bit. i dunno. i did a portscan 

lynn@mail:/bin$ nmap -v -p32400 --open  -r 192.168.0.252
nmap: /usr/lib/plexmediaserver/libcrypto.so.1.0.0: no version information available (required by nmap)
nmap: /usr/lib/plexmediaserver/libssl.so.1.0.0: no version information available (required by nmap)

Starting Nmap 7.01 ( https://nmap.org ) at 2017-03-11 07:04 EST
Initiating Ping Scan at 07:04
Scanning 192.168.0.252 [2 ports]
Completed Ping Scan at 07:04, 0.00s elapsed (1 total hosts)
Initiating Parallel DNS resolution of 1 host. at 07:04
Completed Parallel DNS resolution of 1 host. at 07:04, 0.04s elapsed
Initiating Connect Scan at 07:04
Scanning 192.168.0.252 [1 port]
Completed Connect Scan at 07:04, 0.00s elapsed (1 total ports)
Read data files from: /usr/bin/../share/nmap
Nmap done: 1 IP address (1 host up) scanned in 0.14 seconds

this is the result. 

I checked to make sure they were on the same subnet, as an idiot check. it's a residential network so I don't see myself exceeding 255 devices connected to the network lol. but i checked it using ifconfig on the server

192.168.0.252

the laptop is running windows so i checked it with ipconfig with a result of 

192.168.0.188

so yes they're on the same subnet.

 

if i'm just dumb and missed a function in that command to tell me which ports are open, just lemme know.

[Just.Oblivious]

Let's go back to basics...

 

Have you tried pinging the Ubuntu server from the Windows machine? What was the result?

[whiteGloveReview]

1 minute ago, Just.Oblivious said:

Let's go back to basics...

 

Have you tried pinging the Ubuntu server from the Windows machine? What was the result?

C:\Users\Lisa>ping 192.168.0.252

Pinging 192.168.0.252 with 32 bytes of data:
Reply from 192.168.0.252: bytes=32 time=2ms TTL=64
Reply from 192.168.0.252: bytes=32 time=2ms TTL=64
Reply from 192.168.0.252: bytes=32 time=2ms TTL=64
Reply from 192.168.0.252: bytes=32 time=2ms TTL=64

Ping statistics for 192.168.0.252:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 2ms, Maximum = 2ms, Average = 2ms

 

[Just.Oblivious]

Great, they can communicate with each other on the network.

 

Now you have to determine if the Plex service on the Ubuntu server is actually listening for incoming connections.

 

Run this command on the Ubuntu server :

netstat -tulpn

 

[whiteGloveReview]

2 minutes ago, Just.Oblivious said:

Great, they can communicate with each other on the network.

 

Now you have to determine if the Plex service on the Ubuntu server is actually listening for incoming connections.

 

Run this command on the Ubuntu server :

netstat -tulpn

 

lynn@mail:/bin$ netstat -tulpn
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.1:10024         0.0.0.0:*               LISTEN      -
tcp        0      0 127.0.0.1:10025         0.0.0.0:*               LISTEN      -
tcp        0      0 127.0.0.1:10026         0.0.0.0:*               LISTEN      -
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:587             0.0.0.0:*               LISTEN      -
tcp        0      0 127.0.0.1:9998          0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:110             0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:143             0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:10000           0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      -
tcp        0      0 127.0.0.1:24            0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:443             0.0.0.0:*               LISTEN      -
tcp        0      0 127.0.0.1:4190          0.0.0.0:*               LISTEN      -
tcp        0      0 127.0.0.1:20000         0.0.0.0:*               LISTEN      -
tcp        0      0 127.0.0.1:7777          0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:993             0.0.0.0:*               LISTEN      -
tcp        0      0 0.0.0.0:995             0.0.0.0:*               LISTEN      -
tcp6       0      0 :::587                  :::*                    LISTEN      -
tcp6       0      0 :::110                  :::*                    LISTEN      -
tcp6       0      0 :::143                  :::*                    LISTEN      -
tcp6       0      0 :::10000                :::*                    LISTEN      -
tcp6       0      0 :::22                   :::*                    LISTEN      -
tcp6       0      0 :::25                   :::*                    LISTEN      -
tcp6       0      0 :::993                  :::*                    LISTEN      -
tcp6       0      0 :::995                  :::*                    LISTEN      -
udp        0      0 0.0.0.0:50844           0.0.0.0:*                           -
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           -
udp        0      0 0.0.0.0:10000           0.0.0.0:*                           -
udp6       0      0 :::47678                :::*                                -
udp6       0      0 :::5353                 :::*                                -

it isn't. on that port. so now the question is, what is it on?

[Just.Oblivious]

Rut it as root to show program names:

 

sudo netstat -tulpn

That should help.

 

Services listening on 127.0.0.1 are not reachable from the outside. Plex should be listening on 0.0.0.0 or 192.168.0.x (if it's running and correctly configured).

[whiteGloveReview]

5 minutes ago, Just.Oblivious said:

Rut it as root to show program names:

 

sudo netstat -tulpn

That should help.

 

Services listening on 127.0.0.1 are not reachable from the outside. Plex should be listening on 0.0.0.0 or 192.168.0.x (if it's running and correctly configured).

Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 127.0.0.1:10024         0.0.0.0:*               LISTEN      5331/amavisd-new (m
tcp        0      0 127.0.0.1:10025         0.0.0.0:*               LISTEN      2134/master
tcp        0      0 127.0.0.1:10026         0.0.0.0:*               LISTEN      5331/amavisd-new (m
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      1387/mysqld
tcp        0      0 0.0.0.0:587             0.0.0.0:*               LISTEN      2134/master
tcp        0      0 127.0.0.1:9998          0.0.0.0:*               LISTEN      5331/amavisd-new (m
tcp        0      0 0.0.0.0:110             0.0.0.0:*               LISTEN      1686/dovecot
tcp        0      0 0.0.0.0:143             0.0.0.0:*               LISTEN      1686/dovecot
tcp        0      0 0.0.0.0:10000           0.0.0.0:*               LISTEN      2069/perl
tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      1746/nginx -g daemo
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      1302/sshd
tcp        0      0 127.0.0.1:24            0.0.0.0:*               LISTEN      1686/dovecot
tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      2134/master
tcp        0      0 0.0.0.0:443             0.0.0.0:*               LISTEN      1746/nginx -g daemo
tcp        0      0 127.0.0.1:4190          0.0.0.0:*               LISTEN      1686/dovecot
tcp        0      0 127.0.0.1:20000         0.0.0.0:*               LISTEN      1892/sogod
tcp        0      0 127.0.0.1:7777          0.0.0.0:*               LISTEN      1957/python
tcp        0      0 0.0.0.0:993             0.0.0.0:*               LISTEN      1686/dovecot
tcp        0      0 0.0.0.0:995             0.0.0.0:*               LISTEN      1686/dovecot
tcp6       0      0 :::587                  :::*                    LISTEN      2134/master
tcp6       0      0 :::110                  :::*                    LISTEN      1686/dovecot
tcp6       0      0 :::143                  :::*                    LISTEN      1686/dovecot
tcp6       0      0 :::10000                :::*                    LISTEN      2069/perl
tcp6       0      0 :::22                   :::*                    LISTEN      1302/sshd
tcp6       0      0 :::25                   :::*                    LISTEN      2134/master
tcp6       0      0 :::993                  :::*                    LISTEN      1686/dovecot
tcp6       0      0 :::995                  :::*                    LISTEN      1686/dovecot
udp        0      0 0.0.0.0:50844           0.0.0.0:*                           1123/avahi-daemon:
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           1123/avahi-daemon:
udp        0      0 0.0.0.0:10000           0.0.0.0:*                           2069/perl
udp6       0      0 :::47678                :::*                                1123/avahi-daemon:
udp6       0      0 :::5353                 :::*                                1123/avahi-daemon:

nope.

[Just.Oblivious]

Try restarting the Plex daemon:

sudo service plexmediaserver stop
sudo service plexmediaserver start

Check for any startup errors.

[whiteGloveReview]

13 hours ago, Just.Oblivious said:

Try restarting the Plex daemon:

sudo service plexmediaserver stop
sudo service plexmediaserver start

Check for any startup errors.

nope, nothing.

[whiteGloveReview]

for the record, this has become off topic. so I'm gonna mark this as "solved" and start a new topic elsewhere to diagnose the plex problems.