RFC1395

Network Working Group J. Reynolds Request for Comments: 1395 ISI Obsoletes: 1084, 1048 January 1993 Updates: 951

              BOOTP Vendor Information Extensions

Status of this Memo This memo is a status report on the vendor information extensions used in the Bootstrap Protocol (BOOTP). Distribution of this memo is unlimited. Introduction This RFC is a slight revision and extension of RFC-1048 by Philip Prindeville, who should be credited with the original work in this memo. This memo will be updated as additional tags are are defined. This edition introduces Tag 14 for Merit Dump File, Tag 15 for Domain Name, Tag 16 for Swap Server and Tag 17 for Root Path. 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- 1034]), 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. 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
        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-
        1034].
     Log Server Field (Tag: 7, Data: N address bytes)
        Specifies the IP addresses of N/4 MIT-LCS UDP log server
        [LOGGING].
     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.
     Boot File Size (Tag: 13, Data: 2)
        A two octet value (in network order) specifying the number
        of 512 octet blocks in the default boot file.  Informs BOOTP
        client how large the BOOTP file image is.
     Merit Dump File (Tag: 14, Data: N bytes of filename)
        Name of a file to dump core of this client to.

     Domain Name  (Tag: 15, Data: N bytes of domain name)
        Specifies the domain name of the client for Domain Name
        Server (DNS) resolution [RFC-1034].
     Swap Server (Tag: 16, Data: 4 address bytes)
        An IP address to hold the IP address of a swap server.
     Root Path  (Tag: 17, Data: N bytes of path name)
        A string to specify a pathname to mount as a root disk.
     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:

      Internet Assigned Numbers Authority (IANA)
      Information Sciences Institute
      University of Southern California
      4676 Admiralty Way
      Marina del Rey, California  90292-6695
      or by email as: [email protected]

Implementation specific use of undefined generic types (those in the range 18-127) may conflict with other implementations, and registration is required. 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. 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 The following people provided helpful comments on the first edition of 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 (BOOTP)",

           Stanford and SUN Microsystems, September 1985.

[RFC-903] Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A

           Reverse Address Resolution Protocol", RFC 903, Stanford,
           June 1984.

[RFC-887] Accetta, M., "Resource Location Protocol", RFC 887, CMU,

           December 1983.

[RFC-1034] Mockapetris, P., "Domain Names - Concepts and

           Facilities", STD 13, RFC 1034, USC/Information Sciences
           Institute, November 1987.

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

           Procedure", STD 5, RFC 950, USC/Information Sciences
           Institute, August 1985.

[RFC-868] Postel, J., "Time Protocol", STD 26, RFC 868,

           USC/Information Sciences Institute, May 1983.

[IEN-116] Postel, J., "Internet Name Server", USC/Information

           Sciences Institute, 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", STD 23, RFC 865,

           USC/Information Sciences Institute, 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.

Security Considerations Security issues are not discussed in this memo. Author's Address: Joyce K. Reynolds Information Sciences Institute University of Southern California 4676 Admiralty Way Marina del Rey, CA 90292 Phone: (310) 822-1511 EMail: [email protected]