Self Assigned IP from my macbook pro to xbox through ethernet...

Question

I live in a college dorm and i have been using internet sharing through an ethernet cable to connect to xbox live and it has been working fine for months now, but has now recently decided to make everything difficult and it continuously just says self assigned IP address cannot connect to internet. Every video and forum I have tried reading generally refers back to something involving the router however in this case my wifi is working no problem its just the ethernet cable going to my xbox that has the self assigned IP problem. If anyone could help me it would be greatly appreciated, thank you! 

Answer 1

It isn't clear what you are trying to do.  Why are you connected to the Xbox?  Is the Xbox suppose to share the internet through your mac?
Since there is so little information, I'm going to go through a lot of stuff you might already know.
You have two network interfaces on your Mac.  en0 which is the cable and en1 which is the wireless.
IP addresses are assigned through a process called DHCP.  When you have a self-assigned address there is no DHCP server.
The DHCP server -may- be on a router or it may be on several different devices such as a Unix computer (or Linux) specifically set up to provide DHCP addresses.  Since you are in a dorm, is is quite likely a specifically configured host is providing DHCP.
Your wireless network will get a different DHCP address than your wired network.  For example, 128.1.0.0/16 might be the network assigned to the wireless to support 253x253 different hosts (a lot of hosts and the main reason to keep DHCP off of the router).  And something like 129.1.0.0/16 would be assigned to the wired network.
The DHCP server for the wireless network WILL NOT provide an address for en0.
NOTE: I have never used Apple's Internet Sharing and I -assume- that when you share that the Mac acts like a bridge.
I also assume that this is what you are attempting to do with your Xbox.  This would mean that the Xbox would have to initiate a DHCP request for an address that is forwarded (bridged) through the Mac to the DHCP server.  This request includes the Xbox hardware address.  Now comes the part that is going to make you cry.  MAC addresses are 48 bits and look like AB:CD:EF:12:34:56.  The first 24-bits are assigned to a manufacturer and used for specific products.  When the DHCP request gets to the DHCP server, it knows that the request is from an Xbox.  Your campus may have decided that you've been playing too many games and does not respond with an IP address for the Xbox.
You can check this out by using a tool called tcpdump or you can install Wireshark.  If you want to go down this rabbit hole, it is going to require quite a bit of time and you'll end up becoming quite well educated in how networking works.  People go to school for years to understand this.  :-)
Or, maybe you just forgot to ensure internet sharing was on.
If you have some other kind of wiring setup then perhaps you have a different problem.
BTW, when you plug the ethernet cable from the Xbox into the mac that "activates" it. 
By default OSX is configured to use DHCP to provide an address.
If the Mac sends out DHCP requests over the ethernet cable and never gets a response it will then self-assign an address.
A self-assigned address cannot be used to get to the internet.
(But, I understand that it your Xbox that isn't working not the Mac, especially since you were able to post your question here.)