RFC1048

Network Working Group P. Prindeville Request for Comments: 1048 McGill University

                                                          February 1988

                 BOOTP Vendor Information Extensions

Status of this Memo

  This memo proposes an addition to the Bootstrap Protocol (BOOTP).
  Comments and suggestions for improvements are sought.  Distribution
  of this memo is unlimited.

Introduction

  As workstations and personal computers proliferate on the Internet,
  the administrative complexity of maintaining a network is increased
  by an order of magnitude.  The assignment of local network resources
  to each client represents one such difficulty.  In most environments,
  delegating such responsibility to the user is not plausible and,
  indeed, the solution is to define the resources in uniform terms, and
  to automate their assignment.

  The basic Bootstrap Protocol [RFC-951] dealt with the issue of
  assigning an internet address to a client, as well as a few other
  resources.  The protocol included provisions for vendor-defined
  resource information.

  This memo defines a (potentially) vendor-independent interpretation
  of this resource information.

Overview of BOOTP

  While the Reverse Address Resolution (RARP) Protocol [RFC-903] may be
  used to assign an IP address to a local network hardware address, it
  provides only part of the functionality needed.  Though this protocol
  can be used in conjunction with other supplemental protocols (the
  Resource Location Protocol [RFC-887], the Domain Name System [RFC-
  883]), a more integrated solution may be desirable.

  Bootstrap Protocol (BOOTP) is a UDP/IP-based protocol that allows a
  booting host to configure itself dynamically, and more significantly,
  without user supervision.  It provides a means to assign a host its
  IP address, a file from which to download a boot program from some
  server, that server's address, and (if present) the address of an
  Internet gateway.

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  One obvious advantage of this procedure is the centralized management
  of network addresses, which eliminates the need for per-host unique
  configuration files.  In an environment with several hundred hosts,
  maintaining local configuration information and operating system
  versions specific to each host might otherwise become chaotic.  By
  categorizing hosts into classes and maintaining configuration
  information and boot programs for each class, the complexity of this
  chore may be reduced in magnitude.

BOOTP Vendor Information Format

  The full description of the BOOTP request/reply packet format may be
  found in [RFC-951].  The rest of this document will concern itself
  with the last field of the packet, a 64 octet area reserved for
  vendor information, to be used in a hitherto unspecified fashion.  A
  generalized use of this area for giving information useful to a wide
  class of machines, operating systems, and configurations follows.  In
  situations where a single BOOTP server is to be used among
  heterogeneous clients in a single site, a generic class of data may
  be used.

  Vendor Information "Magic Cookie"

     As suggested in [RFC-951], the first four bytes of this field have
     been assigned to the magic cookie, which identifies the mode in
     which the succeeding data is to be interpreted.  The value of the
     magic cookie is the 4 octet dotted decimal 99.130.83.99 (or
     hexadecimal number 63.82.53.63) in network byte order.

  Format of Individual Fields

     The vendor information field has been implemented as a free
     format, with extendable tagged sub-fields.  These sub-fields are
     length tagged (with exceptions; see below), allowing clients not
     implementing certain types to correctly skip fields they cannot
     interpret.  Lengths are exclusive of the tag and length octets;
     all multi-byte quantities are in network byte-order.

     Fixed Length Data

        The fixed length data are comprised of two formats.  Those that
        have no data consist of a single tag octet and are implicitly
        of one-octet length, while those that contain data consist of
        one tag octet, one length octet, and length octets of data.

        Pad Field (Tag: 0, Data: None)

           May be used to align subsequent fields to word boundaries

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           required by the target machine (i.e., 32-bit quantities such
           as IP addresses on 32-bit boundaries).

        Subnet Mask Field (Tag: 1, Data: 4 subnet mask bytes)

           Specifies the net and local subnet mask as per the standard
           on subnetting [RFC-950].  For convenience, this field must
           precede the GATEWAY field (below), if present.

        Time Offset Field (Tag: 2, Data: 4 time offset bytes)

           Specifies the time offset of the local subnet in seconds
           from Coordinated Universal Time (UTC); signed 32-bit
           integer.

        End Field (Tag: 255, Data: None)

           Specifies end of usable data in the vendor information area.
           The rest of this field should be filled with PAD zero)
           octets.

     Variable Length Data

        The variable length data has a single format; it consists of
        one tag octet, one length octet, and length octets of data.

        Gateway Field (Tag: 3, Data: N address bytes)

           Specifies the IP addresses of N/4 gateways for this subnet.
           If one of many gateways is preferred, that should be first.

        Time Server Field (Tag: 4, Data: N address bytes)

           Specifies the IP addresses of N/4 time servers [RFC-868].

        IEN-116 Name Server Field (Tag: 5, Data: N address bytes)

           Specifies the IP addresses of N/4 name servers [IEN-116].

        Domain Name Server Field (Tag: 6, Data: N address bytes)

           Specifies the IP addresses of N/4 domain name servers RFC-
           883].

        Log Server Field (Tag: 7, Data: N address bytes)

           Specifies the IP addresses of N/4 MIT-LCS UDP log server
           [LOGGING].

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        Cookie/Quote Server Field (Tag: 8, Data: N address bytes)

           Specifies the IP addresses of N/4 Quote of the Day servers
           [RFC-865].

        LPR Server Field (Tag: 9, Data: N address bytes)

           Specifies the IP addresses of N/4 Berkeley 4BSD printer
           servers [LPD].

        Impress Server Field (Tag: 10, Data: N address bytes)

           Specifies the IP addresses of N/4 Impress network image
           servers [IMAGEN].

        RLP Server Field (Tag: 11, Data: N address bytes)

           Specifies the IP addresses of N/4 Resource Location Protocol
           (RLP) servers [RFC-887].

        Hostname (Tag: 12, Data: N bytes of hostname)

           Specifies the name of the client. The name may or may not
           domain qualified: this is a site-specific issue.

        Reserved Fields (Tag: 128-254, Data: N bytes of undefined
        content)

           Specifies additional site-specific information, to be
           interpreted on an implementation-specific basis.  This
           should follow all data with the preceding generic tags 0-
           127).

Extensions

  Additional generic data fields may be registered by contacting:

         Joyce K. Reynolds
         USC - Information Sciences Institute
         4676 Admiralty Way
         Marina del Rey, California  90292-6695

         or by E-mail as: [email protected]
         (nic handle JKR1).

  Implementation specific use of undefined generic types (those in the
  range 12-127) may conflict with other implementations, and
  registration is required.

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  When selecting information to put into the vendor specific area, care
  should be taken to not exceed the 64 byte length restriction.
  Nonessential information (such as host name and quote of the day
  server) may be excluded, which may later be located with a more
  appropriate service protocol, such as RLP or the WKS resource-type of
  the domain name system.  Indeed, even RLP servers may be discovered
  using a broadcast request to locate a local RLP server.

Comparison to Alternative Approaches

  Extending BOOTP to provide more configuration information than the
  minimum required by boot PROMs may not be necessary.  Rather than
  having each module in a host (e.g., the time module, the print
  spooler, the domain name resolver) broadcast to the BOOTP server to
  obtain the addresses of required servers, it would be better for each
  of them to multicast directly to the particular server group of
  interest, possibly using "expanding ring" multicasts.

  The multicast approach has the following advantages over the BOOTP
  approach:

   - It eliminates dependency on a third party (the BOOTP server) that
   may be temporarily unavailable or whose database may be incorrect or
   incomplete.  Multicasting directly to the desired services will
   locate those servers that are currently available, and only those.

   - It reduces the administrative chore of keeping the (probably
   replicated) BOOTP database up-to-date and consistent.  This is
   especially important in an environment with a growing number of
   services and an evolving population of servers.

   - In some cases, it reduces the amount of packet traffic and/or the
   delay required to get the desired information.  For example, the
   current time can be obtained by a single multicast to a time server
   group which evokes replies from those time servers that are
   currently up.  The BOOTP approach would require a broadcast to the
   BOOTP server, a reply from the BOOTP server, one or more unicasts to
   time servers (perhaps waiting for long timeouts if the initially
   chosen server(s) are down), and finally a reply from a server.

  One apparent advantage of the proposed BOOTP extensions is that they
  provide a uniform way to locate servers.  However, the multicast
  approach could also be implemented in a consistent way across
  multiple services.  The V System naming protocol is a good example of
  this; character string pathnames are used to name any number of
  resources (i.e., not just files) and a standard subroutine library
  looks after multicasting to locate the resources, caching the
  discovered locations, and detecting stale cache data.

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  Another apparent advantage of the BOOTP approach is that it allows an
  administrator to easily control which hosts use which servers.  The
  multicast approach favors more distributed control over resource
  allocation, where each server decides which hosts it will serve,
  using whatever level of authentication is appropriate for the
  particular service.  For example, time servers usually don't care who
  they serve (i.e., administrative control via the BOOTP database is
  unnecessary), whereas file servers usually require strong
  authentication (i.e., administrative control via the BOOTP database
  is insufficient).

  The main drawback of the multicast approach, of course, is that IP
  multicasting is not widely implemented, and there is a need to locate
  existing services which do not understand IP multicasts.

  The BOOTP approach may be most efficient in the case that all the
  information needed by the client host is returned by a single BOOTP
  reply and each program module simply reads the information it needs
  from a local table filled in by the BOOTP reply.

Acknowledgments

  I would like to thank the following persons for their helpful
  comments and insights into this memo: Drew Perkins, of Carnagie
  Mellon University, Bill Croft, of Stanford University, and co-author
  of BOOTP, and Steve Deering, also of Stanford University, for
  contributing the "Comparison to Alternative Approaches" section.

References

  [RFC-951]   Croft, B., and J. Gilmore, "Bootstrap Protocol", Network
              Information Center, SRI International, Menlo Park,
              California, September 1985.

  [RFC-903]   Finlayson, R., T. Mann, J. Mogul, and M. Theimer, "A
              Reverse Address Resolution Protocol", Network Information
              Center, SRI International, Menlo Park, California, June
              1984.

  [RFC-887]   Accetta, M., "Resource Location Protocol", Network
              Information Center, SRI International, Menlo Park,
              California, December 1983.

  [RFC-883]   Mockapetris, P., "Domain Name - Implementation and
              Specification", Network Information Center, SRI
              International, Menlo Park, California, November 1983.

  [RFC-950]   Mogul, J., "Internet Standard Subnetting Procedure",

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              Network Information Center, SRI International, Menlo
              Park, California, August 1985.

  [RFC-868]   Postel, J., "Time Protocol", Network Information Center,
              SRI International, Menlo Park, California, May 1983.

  [IEN-116]   Postel, J., "Internet Name Server", Network Information
              Center, SRI International, Menlo Park, California, August
              1979.

  [LOGGING]   Clark, D., Logging and Status Protocol", Massachusetts
              Institute of Technology Laboratory for Computer Science,
              Cambridge, Massachusetts, 1981.

  [RFC-865]   Postel, J., "Quote of the Day Protocol", Network
              Information Center, SRI International, Menlo Park,
              California, May 1983.

  [LPD]       Campbell, R., "4.2BSD Line Printer Spooler Manual", UNIX
              Programmer's Manual, Vol II,  University of California at
              Berkeley, Computer Science Division, July 1983.

  [IMAGEN]    "Image Server XT Programmer's Guide", Imagen Corporation,
              Santa Clara, California, August 1986.

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