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ITS Networking & Telecommunications

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. (Specifically: "...routing information about private networks shall not be propagated on inter-enterprise links, and packets with private source or destination addresses should not be forwarded across such links." RFC1918 — Address Allocation for Private Internets.)

Organizationally-Scoped (aka Private) IP Address Space

Prefix First Address Last Address Number of
Addresses
10.0.0.0/8 10.0.0.0 10.255.255.255 16,777,216
172.16.0.0/12 172.16.0.0 172.31.255.255 1,048,576
192.168.0.0/16 192.168.0.0 192.168.255.255 65,536

 

Assigning Private IP Network Numbers

RFC1918 does not explicitly define "enterprise"; it could be interpreted as "the University of Michgan", or as the UM-Ann Arbor Campus (with the Flint and Dearborn campuses each being independent enterprises), or as the UMnet backbone (with the UMHS backbone being an independent enterprise), or one could consider each school/​college/​unit as a separate enterprise.

Historically, we have considered the Ann Arbor campus to be the "enterprise", and private IP address space on the Ann Arbor campus has been divided up between the three backbone providers: ITCom (UMnet), College of Engineering (CoE), and UMHS (see below). Each of these is responsible for administration of prefixes 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 UM-Ann Arbor campus. "Backbone-local" ranges will not be routed between the Ann Arbor backbones.

In September 2003, one block of private IP space (172.31.0.0/17) was made routable between the UMnet backbone and the UM-Dearborn campus. At the same time another block (172.31.128.0/17) was set aside for possible future routing between the Ann Arbor campus and UM-Flint. In addition, the 10.215.0.0/16 and 10.216.0.0/16 blocks have been reserved for possible inter-campus routing with Dearborn and Flint, respectively (see below).

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

10.0.0.0/8 Assignments

Table 1: 10.0.0.0/8 Assignments

Backbone Prefix First Address Last Address Announcement
any 10.0.0.0/9 10.0.0.0 10.127.255.255 Not announced by any backbone*
UMHS 10.128.0.0/11 10.128.0.0 10.159.255.255 May be announced by UMHS
CoE 10.160.0.0/11 10.160.0.0 10.191.255.255 May be announced by CoE
shared 10.192.0.0/11 10.192.0.0 10.223.255.255 Announcements by mutual agreement**
UMnet 10.224.0.0/11*** 10.224.0.0 10.255.255.255 May be announced by UMnet*

* There are exceptions; see table 1a below.
** See table 1b below.
*** 10.255.0.0/16 is reserved for "LAN-local" use, i.e. it may be used freely on any local network and will never be routed across the UMnet backbone.

 

Note: Within UMnet, prefixes that start with 10.75, 10.108, 10.194, 10.211 and 10.213 are meant to mirror prefixes that start with 207.75, 198.108, 67.194, 141.211 and 141.213. These private IP prefixes are reserved for use on the networks where the mirrored public IP prefixes are used. Units needing private IP space can generally assume that these prefixes will be available for intra-campus use. Please contact umnet-administration@umich.edu to arrange for the activation of these private prefixes.

 

Table 1a: 10.0.0.0/8 Assignment Exceptions

Prefix Announced by Comments
10.75.144.0/20 UMnet mirror of 207.75.144.0/20
10.108.8.0/21 UMnet mirror of 198.108.8.0/21
10.111.0.0/16 ITCom Eng Lab mirror of 198.111.0.0/16
10.255.0.0/16 not routed LAN-Local

 

Table 1b: 10.0.0.0/8 Prefixes Announced by Mutual Agreement

Prefix Announced by Comments
10.194.0.0/16 UMnet mirror of 67.194.0.0/16
10.200.0.0/22 UMnet Bioinformatics
10.211.0.0/16 UMnet mirror of 141.211.0.0/16
10.212.0.0/16 CoE, UMnet mirror of 141.212.0.0/16
10.213.0.0/17 CoE, UMnet mirror of 141.213.0.0/17
10.213.128.0/17 UMnet mirror of 141.213.128.0/17
10.214.0.0/16 UMHS mirror of 141.214.0.0/16
10.215.0.0/16 UM-Dearborn mirror of 141.215.0.0/16
10.216.0.0/16 UM-Flint mirror of 141.216.0.0/16

 

172.16.0.0/12 Assignments

Table 2: 172.16.0.0/12 Assignments

Backbone Prefix First Address Last Address Announcement Comments
UMHS 172.16.0.0/16 172.16.0.0 172.16.255.255 May be announced by UMHS
UMHS 172.17.0.0/16 172.17.0.0 172.17.255.255 May be announced by UMHS
none 172.18.0.0/16 172.18.0.0 172.18.255.255 Not announced Reserved for future use
none 172.19.0.0/16 172.19.0.0 172.19.255.255 Not announced Reserved for future use
any 172.20.0.0/16 172.20.0.0 172.20.255.255 Not announced
CoE 172.21.0.0/16 172.21.0.0 172.21.255.255 May be announced by CoE
any 172.22.0.0/16 172.22.0.0 172.22.255.255 Not announced
UMnet 172.23.0.0/16 172.23.0.0 172.23.255.255 May be announced by UMnet
any 172.24.0.0/16 172.24.0.0 172.24.255.255 Not announced
any 172.25.0.0/16 172.25.0.0 172.25.255.255 Not announced
any 172.26.0.0/16 172.26.0.0 172.26.255.255 Not announced
none 172.27.0.0/16 172.27.0.0 172.27.255.255 Not announced Reserved for future use
UMnet 172.28.0.0/16 172.28.0.0 172.28.255.255 may be announced by UMnet VoIP
CoE 172.29.0.0/16 172.29.0.0 172.29.255.255 may be announced by CoE VoIP
UMHS 172.30.0.0/16 172.30.0.0 172.30.255.255 may be announced by UMHS VoIP
UM-Dearborn 172.31.0.0/17 172.31.0.0 172.31.127.255 may be announced by UM-Dearborn VoIP
UM-Flint 172.31.128.0/17 172.31.128.0 172.31.255.255 may be announced by UM-Flint VoIP

 

192.168.0.0/16 Assignments

Table 3: 192.168.0.0/16 Assignments

Backbone Prefix First Address Last Address Announcement Comments
shared 192.168.0/18 192.168.0.0 192.168.63.255 Announcements by mutual agreement
any 192.168.64/18 192.168.64.0 192.168.127.255 Not announced
any 192.168.128.0/17 192.168.128.0 192.168.255.255 Not announced

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.

 

Adjustments to the Private IP Assignments

If the University of Michigan Private IP Network Assignments need to be adjusted, UMnet and UMHS must be informed. The current contact for each campus is:

Campus Contact(s) Email Address
Medical Campus UMHS Networking mcit-iso-networking@med.umich.edu
All Others UMnet Administration umnet-administration@umich.edu

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

 

 

This document is brought to you by UMnet Administration (umnet-administration@umich.edu)

 

Last update: 2015-02-05