Default IP Routers, Network Masks, and Broadcast Addresses

Most devices attached to the campus network learn the IP address of their default IP router (a.k.a "gateway") via DHCP or BootP. Some do so by listening to RIPv1 routing announcements. If your device cannot use any of those methods, you may use this table to learn the IP address of the appropriate default IP router (a.k.a "gateway"), so you may manually configure your device with this information.

Most devices attached to the campus network learn the IP network mask (a.k.a. "subnet mask", or "netmask") via DHCP or BootP. If your device cannot use either of those methods, you may use this table to learn the appropriate network mask, so you may manually configure your device with this information.

Some devices attached to the campus network learn the IP broadcast address via DHCP or BootP. If your device cannot use either of those methods, you may use this table to learn the appropriate IP broadcast address, so you may manually configure your device with this information.

In the first column, locate the range of IP addresses that include the IP address already assigned to your computer. In the second column, you can read off the appropriate default router IP address. In the third column you can read off the network mask, and the fourth column shows the broadcast address.

For example: if your IP address is 128.112.177.234, then the IP address of the default IP router is 128.112.176.1, the network mask is 255.255.252.0, and the broadcast address is 128.112.176.0.

This document does not include information for External Customer Networks. For IP ranges, network masks, and default IP routers for those networks, see External Customer Network Assignments.

Notes

1. The recommended address is 128.112.144.1. However, the older address 128.112.144.248 will also work and continues to be supported. (Don't use both; they are actually both the same device.)

2. There is no default IP router for this network; it is isolated, not routed to any other network.

3. For devices registered in the Host Database before October 30 2001, the old default IP router 128.112.204.1 and old subnet mask 255.255.252.0 also continue to work in most cases. The only case that will not work is if the device was using the old broadcast address 128.112.204.0; in that case, the device should be reconfigured to use the new network mask 255.255.248.0, new broadcast address 128.112.200.0, and new default router 128.112.200.1 (the old default router 128.112.204.1 will also still work).

   Any older device may be reconfigured to use the new values for improved performance; if reconfigured, the device must use all the new values, not a combination of old and new values.

   For devices registered starting October 30 2001, the new subnet mask 255.255.248.0 and new broadcast address 128.112.204.0 must be used; these devices may use either the old default router 128.112.204.1 or the new default router 128.112.200.1.

4. For devices registered in the Host Database before August 12 2003, the old default IP router 128.112.44.1 and old subnet mask 255.255.252.0 also continue to work in most cases. The only case that will not work is if the device was using the old broadcast address 128.112.44.0; in that case, the device should be reconfigured to use the new network mask 255.255.248.0, new broadcast address 128.112.40.0, and new default router 128.112.40.1 (the old default router 128.112.44.1 will also still work).

   Any older device may optionally be reconfigured to use the new values for improved performance; if reconfigured, the device must use all the new values, not a combination of old and new values.

   For devices registered starting August 12 2003, the new subnet mask 255.255.248.0 and new broadcast address 128.112.40.0 must be used; these devices may use either the old default router 128.112.44.1 or the new default router 128.112.40.1.

5. For devices registered in the Host Database before June 22 2005, the old default IP router 128.112.188.1 and old subnet mask 255.255.252.0 also continue to work in most cases. The only case that will not work is if the device was using the old broadcast address 128.112.188.0; in that case, the device should be reconfigured to use the new network mask 255.255.248.0, new broadcast address 128.112.184.0, and new default router 128.112.184.1 (the old default router 128.112.188.1 will also still work).

   Any older device may be reconfigured to use the new values for improved performance; if reconfigured, the device must use all the new values, not a combination of old and new values.

   For devices registered starting June 22 2005, the new subnet mask 255.255.248.0 and new broadcast address 128.112.184.0 must be used; these devices may use either the old default router 128.112.188.1 or the new one 128.112.184.1.

6. On the morning of November 1 2005, the IP subnet mask changed from 255.255.252.0 to 255.255.248.0. Devices that learned this information via BootP or DHCP (this is most devices) had to be rebooted after 7:00am November 1 2005. Devices that were manually configured needed to be reconfigured to use the new subnet mask and then rebooted after 7:00am November 1 2005.

7. On the morning of July 18 2006, the IP subnet mask changed from 255.255.252.0 to 255.255.248.0. Devices that learned this information via BootP or DHCP (this is most devices) had to be rebooted after 5:30am July 18 2006 (but no later than September 1 2006) to learn of the change. Devices that were manually configured needed to be reconfigured to use the new subnet mask and then rebooted; this can happen anytime (but no later than September 1 2006). We recommended that Windows systems attached to this subnet all be made to change together, during 5:30 am - 7:00 am July 18 2006; while in transition, some services provided by those Windows systems may not work properly.

8. The subnet mask changed from 255.255.252.0 to 255.255.254.0 on March 7 2007.

9. This network range is allocated to a private network; the customer responsible for it has further subnetting it and manages the address space and routers. Contact the customer responsible for the private network to determine an appropriate subnet mask, IP router, and broadcast address.