IP Address Categories

In order to communicate on the CWU network, a device must be assigned an Internet Protocol (IP) address. For client devices, dynamic addresses are typically assigned automatically via the Dynamic Host Configuration Protocol (DHCP). For servers, static addresses may be assigned by DHCP or they may be hard-coded in the server's configuration. It's simple to determine the IP address your device has been assigned.

On Windows, open a command prompt window and execute ipconfig:

On a Mac or Linux host, open a terminal window and execute /sbin/ifconfig:

On a mobile device, the location of this information will vary with platform, but you will typically find it somewhere within the Settings app.

Identifying where your IP address falls within several broad categories may assist you in troubleshooting connectivity issues:

1. Routable IP addresses - CWU has been assigned several blocks of routable addresses. In general, traffic sourced from these addresses can exit the CWU network and traverse the Internet as is, subject to firewall restrictions:
   • 72.233.192.0 - 72.233.255.255: Ellensburg Campus Network. Wired faculty, staff and lab machines are typically assigned addresses in this range.
   • 173.229.54.0 - 173.229.59.255: Centers. End user devices are not assigned addresses in this range directly but are translated to this range at the Internet border.
   • 69.56.96.0 - 69.56.111.255: ResNet. Wired student computers in the residence halls are assigned addresses in this range.Wireless student computers are translated to this range at the Internet border.
   • 216.210.8.0 - 216.210.11.255: ResNet. Wired student computers in the residence halls are assigned addresses in this range.Wireless student computers are translated to this range at the Internet border.
   • Misc. 216.186.x.x addresses: DMZs and testing. These addresses are not assigned to end user computers.
   The sample ifconfig output above from a Linux host is for a routable address. If you have a routable address, you should have connectivity to both internal CWU services and the Internet.
2. Non-routable IP addresses - Request for Comments (RFC) 1918 (http://tools.ietf.org/html/rfc1918) defines ranges of addresses which may only be used internally and cannot traverse the Internet:
   • 10.0.0.0 - 10.255.255.255
   • 172.16.0.0 - 172.31.255.255
   • 192.168.0.0 - 192.168.255.255
   One typical use for these addresses is for internal resources such as printers and servers which need not and/or should not have direct Internet connectivity. On the CWU network you will see many servers and printers whose addresses begin with 172.16. Another use is to support large numbers of devices which cannot be accommodated by an organization's assigned routable address space. At CWU, student and guest wireless devices number in the thousands, so we allocate addresses in the 10.x.x.x range. Traffic sourced from such addresses must undergo network address translation (NAT) at the Internet border before it can leave the CWU network. The sample ipconfig output above is from a Windows server. This server will be able communicate with external web sites if it is configured to use a proxy. However, it cannot communicate with the Internet via protocols other than HTTP/S and FTP since NAT is not configured for it. If you are a server administrator, be aware of the limitations imposed by internal addresses.
3. Link local addresses - If you have an address in this range, more than likely you have a problem. RFC 3927 (http://tools.ietf.org/html/rfc3927) reserves the range 169.254.0.0 - 169.254.255.255 for autoconfiguration of network interfaces. This system permits devices to self-assign IP addresses, avoid conflicts and communicate with one another on the same network segment without configuration by the end user. Addresses in this range are only assigned in the absence of DHCP or manual configuration. Your device should not have such an address if it is connected to the CWU network and functioning properly.

A list of addresses in use at CWU is available at http://netdb.cts.cwu.edu/netdb/segments.html (internal access only).

*Note: This article is applicable only to IPv4 unicast addresses.