Assigning Private IP Network Numbers

Private IP Network Numbers

Private IP networks are "organizationally scoped" IP nets, i.e. networks which institutions can use internally but which are not routed outside of that organization. (For more information, see RFC1918—Address Allocation for Private Internets.)

Organizationally-Scoped (Private) IP Address Space

Class	Starting Address	Ending Address	CIDR Notation	Comments
A	10.0.0.0	10.255.255.255	10/8	16,777,216 addresses
B	172.16.0.0	172.31.255.255	172.16/12	1,048,576 addresses
C	192.168.0.0	192.168.255.255	192.168/16	65,536 addresses

Assigning Private IP Network Numbers

Private IP address space at the University of Michigan has been divided up among the three backbone providers: ITCom (UMnet), CAEN, and UMHS (see below). Each of these is responsible for administration of subnets within its assigned ranges. Ranges of private IP space designated as "shared" may be routed between the three groups—i.e. their scope is the entire U-M Ann Arbor campus. "Backbone-local" ranges will not be routed between the three Ann Arbor backbones.

In September 2003, a block of private IP space (172.31.0.0/17) was made routable between the UMnet backbone and the U-M Dearborn campus (over a direct inter-campus link). At the same time another block (172.31.128.0/17) was set aside for possible future routing between the Ann Arbor campus and U-M Flint.

Units who wish to use private IP addresses on their networks must request address space from their on-campus backbone provider to ensure that addressing conflicts do not occur.

University of Michigan Private IP Network Assignments

*Note: 10.0.0.0/8 addresses which "mirror" the public address spaces currently in use (i.e. networks with prefixes of 10.194, 10.211, 10.212, 10.213, 10.214 and 10.75.<144-159>) are reserved and may be announced only by the appropriate owner; this includes one exception to the "Backbone-local" range (10.0.0.0/9) and several exceptions to the UMHS range (10.128.0.0/11).

**Within UMnet, the 10.255.0.0/16 net is reserved for "LAN-local" use, i.e. it may be used freely on any LAN and will never be routed across the UMnet backbone.

*Within UMnet, 10.75.V, 10.108.W, 10.194.X, 10.211.Y and 10.213.Z subnets that mirror existing 207.75.v, 198.108.w, 67.194.X, 141.211.Y and 141.213.Z subnets are reserved for use on the networks where those public IP subnets reside; units needing private IP space can generally assume that these subnets will be available for intra-campus use. Please contact umnet-admin@umich.edu to arrange for the activation of these private subnets.

Within UMnet, the 192.168.255.0/24 net is reserved for "LAN-local" use, i.e. it may be used freely on any LAN and will never be routed across the UMnet backbone.

If these assignments need to be adjusted, UMnet, UMHS and CAEN must all be informed. The current contacts for the three campuses are:

For information on specific IP subnet assignments (public or private) or other information regarding networks on the UMnet backbone, please visit the Network Information Database page.

The UMnet Administration Team
umnet-admin@umich.edu