Understanding This Network

[sn0wm4n]

I'm trying to understand how this university network works. I'm just gonna make up IPs to explain


My IP on the wifi is 5.5.5.5. Another computer on the same network is 5.5.4.4. The default gateway of the 5.5.5.5 is 5.5.5.1 and the DCHP server for 5.5.5.5 is 5.5.3.3. I'm confused how all this works especially considering were not behind any type of router or anything. My IP is an internet IP, not a local IP like 192.168.x.x or 10.x.x.x.


How is this network set up to give each computer that connects to wireless its own internet IP and how the IPs are determined. Like does the university by a range of IPs from the service provider or what?

[noob]

If your IP is 5.5.5.5 another computer must be 5.5.5.4 ,cannot be 5.5.4.4....
You should read TCP/IP for dummies to undestand how things work.

[sn0wm4n]

I actually have a decent understanding of TCP/IP but I'm not making these IPs up. Connecting to the same access point, I  have the IP 130.32.186.5 and my other computer has the IP 130.32.184.65. These obviously aren't real IPs but they have the same B Class I think is the term (the first two numbers are the same.)

[RedBullAddicted]

Hi Sn0wm4n,

you are right... it depends on the subnet mask if these clients are in the same subnet. 5.5.0.0/21 (255.255.248.0) would include all hosts in the range from 5.5.0.1 - 5.5.7.254 for example. I know there a universities and even companies like HP which bought a huge range of public IP addresses for there clients. If you got a default gateway you are behind a router the default gateway is your next hop to other networks. Would be interesting to know if you need to log in to the wireless network via a webinterface or something like that. Are you able to ping another computer? if your IP is 5.5.5.5 and the other one has 5.5.4.4 as you wrote... do you get an icmp replay? The IP range 5.0.0.0/8 has been assigned in 2010 from IANA to RIPE and is a public range as you already said. Hamachi is using this Range, too which means if you are connected to a hamachi vpn you are not able to access ressources on the internet which use this range.

Cheers,
RBA

[proxx]

This might sound very old fashioned but have you actually performed a traceroute>?

[sn0wm4n]

When I traceroute, the request always times out.


I've connected to my ftp server off site before and my ftp server shows a connection from the same IP given to my computer (the public IP), not the IP of my default gateway or any router I may be behind.


I connected two different wireless cards on the same computer to the same access point. One was given the IP 130.18.234.x with default gateway 130.18.234.1 and the other card was given the IP 172.17.0.x with the default gateway 172.16.0.1. A different computer connecting to the same access point was given the IP 130.18.175.x


Here's another conundrum though. When connecting to the ftp server through 130.18.234.x, it shows that it's connecting through 130.18.234.x. But when I try to connect through 172.17.0.x, the ftp server is showing a connection through 130.18.37.x.  Traceroute doesn't work for either card


Can someone offer an explanation how this works??

[RedBullAddicted]

Hi sn0wm4n,

with the little information given it is not easy to get an idea about the network topology but lets try:

When I traceroute, the request always times out.

I guess you are behind a firewall which drops ICMP packets. You can try it with a tcp traceroute.

I've connected to my ftp server off site before and my ftp server shows a connection from the same IP given to my computer (the public IP), not the IP of my default gateway or any router I may be behind.

As you already have a public IP address the router does not need to NAT a privat address to a public one.

I connected two different wireless cards on the same computer to the same access point. One was given the IP 130.18.234.x with default gateway 130.18.234.1 and the other card was given the IP 172.17.0.x with the default gateway 172.16.0.1. A different computer connecting to the same access point was given the IP 130.18.175.x

I guess your university has some kind of access control with dynamic vlan assignment.  You don't said that you needed to login via a webinterface or some supplicant software. Neither you said you needed to install a certificate or if the computer you use is a private one or one the university provides. If this information is right I guess they are doing the vlan assignment based on MAC address. 130.0.0.0/8 is a public range again and 172.16.0.0/12 is a private range. That means one wlan card was put into the internal network and the other one into the public range. You can try to change the wlan cards MAC address which was placed into the public range to the one which was placed into the privat range. and see what happens to prove me right or wrong

Here's another conundrum though. When connecting to the ftp server through 130.18.234.x, it shows that it's connecting through 130.18.234.x. But when I try to connect through 172.17.0.x, the ftp server is showing a connection through 130.18.37.x.  Traceroute doesn't work for either card

As I said before the 130.0.0.0/8 range is a public range so the router does not need to do NAT. As the other range is a private one your gateway router needs to NAT (network address translation btw.) your privat address to a public one. You can lookup NAT with google or you can have a look at the Tutorial section. Someone wrote a Tutorial about Networking Basics. At the moment I am not sure if it is explained in part one or two

I hope this helps. If you have some more information we can go on with it

Cheers,
RBA

[proxx]

Its also very interesting to test if open ports are directly accesible.
This will tell youa at least something about the restrictions.
Fire up netcat or whatever and try to connect back to the public IP address.

Funny actually.