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DHCP at Stanford

Contents

What is the DHCP standard?

Dynamic Host Configuration Protocol, an internet standard described in RFC 2131, defines how any networked machine can automatically receive an IP address for a specified lease time. According to the full standard, the DHCP client may receive differing IP addresses, depending on time and network location. Clients can also automatically receive other parameters like DNS servers, default gateway, and subnet mask. Clients will attempt to renew their lease after 50% of the lease time from the leasing DHCP server.


Current implementation of DHCP at Stanford

Currently Stanford implements a subset of the full DHCP standard. At Stanford, for security reasons, only machines with registered hardware addresses will receive a statically assigned IP address. BootP is a subset of DHCP which is similar to Stanford's current implementation of DHCP.

Currently, Stanford sets a lease time of 1 day so clients will attempt to renew their lease after 12 hours. Because Windows NT, Windows 95 and MacOS 8.5 do not automatically renew their leases upon reboot, changing the IP address in NetDB for a DHCP client will not propagate at the next NetDB update. Instead, the DHCP client will continue to use its current address until it attempts to renew its lease. To force a client to renew immediately, one must manually release and renew the lease. See "Gotchas" section for detailed directions.

Stanford DHCP servers will respond to DHCP requests approximately 10 minutes after the host entry in NetDB is appropriately entered.

Do not operate your own DHCP server on your network. If you absolutely need to operate your own DHCP server, please work with your network consultant first to make sure your server works with the Stanford DHCP servers. Please note that many wireless devices can be easily set up to be DHCP servers, some do so by default. Also, NAT, which we strongly suggest you not use, can also be used as a DHCP server. Be careful that you don't misconfigure a wireless device or NAT server as a DHCP server.

Roaming DHCP

Roaming DHCP allows hosts to visit or roam to another network and is intended for brief periods- library visits, class time, etc. Hosts located permanently or predominantly on a network should have a permanent IP address on that network. The lease time for Roaming DHCP is currently (3/23/99) 42 minutes. Note that computer and NetDB configuration should be done by the user and the LNA of the user's home network, not by the LNA of the network where the user is roaming. This is especially true when roaming in the Libraries which do not have the staff to support all the roaming laptops.

Requirements

  1. Computer must be using DHCP. When roaming to a new network, release then renew the IP address. (See DHCP Gotchas for details on releasing IP addresses.) Note that DHCP is not implemented on the DSL routers so manual configuration is required at home. When roaming on campus, the computer network configuration should be changed to DHCP. See DHCP at Stanford web page for more details.
  2. Roaming DHCP must be enabled on the visited network. LNA(s) approval is required to implement Roaming DHCP on a given network. Request this via a HelpSU ticket. See Networks with Roaming DHCP Currently Implemented for the current list. It is not necessary for the user to know the IP addresses set aside for Roaming DHCP.
  3. NetDB- machine no longer requires an IP address, but if the user is faculty or staff or an on-campus student, they should be given an IP address in their primary location. In NetDB, under "Interface," enter the correct Hardware address, and check both "DHCP/BootP" and "Roaming," For IP address registration, contact your Departmental LNA or your Residential Computing Consultant. If you live off campus, please contact the ITSS Computer Resouce Center at 5-HELP or HelpSU. Roaming DHCP Address Assignments
    Although an IP address is no longer required for a host to use roaming DHCP, if the computer is used by a faculty or staff member or on-campus student, it should be given a "home" IP address by the owner's department or residence.

    To participate, contact your local network administrator or RCC.


    Roaming DHCP at Stanford University Libraries

    Roaming DHCP is enabled at all libraries.

    Patrons wishing to use network connections in the libraries will need to get their laptops registered in NetDB for roaming. When asked, library staff will provide a sheet of very general directions, and patrons will be directed to contact their departmental LNA's for the registration. Students who are campus residents MUST be directed to their RCC's (Residential Computing Consultants). LNA's in departments should never set up a roaming registration for a residential student's laptop. In the case of departments who don't have LNA's or undeclared students, staff can contact the ITSS Computer Resource Center (5-8181 or http://helpsu.stanford.edu) for the registration.

    It is important to understand that library staff will not be able to troubleshoot problems for patrons. Other than providing a cheat-sheet with very general directions, they will suggest that patrons experiencing problems using roaming dhcp either go back to their LNA's or RCC's, or to the departmental Expert Partners for troubleshooting assistance.


    Gotchas

    Windows 95, Windows NT and MacOS 8.5 do not automatically renew their lease when rebooted. If the machine moves networks, the following must be done:


    References

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    Last revised October 20, 1999. ©1997-1999 Trustees of the Leland Stanford Junior University