rfc898.txt

RFC 相关的技术文档

Network Working Group                                    R. Hinden (BBN)
Request for Comments: 898                                J. Postel (ISI)
                                                          M. Muuss (BRL)
                                                       J. Reynolds (ISI)
                                                              April 1984

              GATEWAY SPECIAL INTEREST GROUP MEETING NOTES

STATUS OF THIS MEMO

   This memo is a report on a meeting.  No conclusions, decisions, or
   policy statements are documented in this note.

INTRODUCTION

   This memo is a report on the Gateway Special Interest Group Meeting
   that was held at ISI in Marina del Rey, California on 28 and 29
   February 1984.  Robert Hinden of BBNCC chaired, and Jon Postel of ISI
   hosted the conference.  Approximately 35 gateway designers and
   implementors attended.  These notes are based on the recollections of
   Jon Postel and Mike Muuss.  Under each topic area are Jon Postel's
   brief notes, and additional details from Mike Muuss.

   The rest of this memo has three sections: the agenda, notes on the
   talks, and the attendees list.

MEETING AGENDA

   Tuesday, February 28

      9:00  Opening Remarks -- BBN - Hinden
      9:15  Opening Remarks -- ISI - Postel
      9:30  The MIT C Gateway -- MIT - Martin
      10:00 The Butterfly Gateway -- BBN - Hinden
      10:30 Break
      11:00 The EGP C Gateway -- ISI - Kirton
      11:20 The BRL Gateway -- BRL - Natalie
      11:40 The CMU Gateway -- CMU - Accetta
      12:00 Lunch
      1:30  The Wisconsin BITNET/CSNET Gateway -- UWisc - Solomon
      2:00  LAN to X.25 Gateway -- Computer Gateways Inc. - Buhr
      2:20  ISI-UCI Gateway -- UCI - Rose
      2:40  FACC Gateway -- FACC - Holkenbrink
      3:00  Break
      3:30  Lincoln IP/ST Gateway -- LL - Forgie/Kantrowitz
      3:50  Minimal Stub Gateways -- MITRE - Nabielsky
      4:10  Discussion







Hinden, Postel, Muuss, & Reynolds                               [Page 1]



RFC 898                                                       April 1984
Gateway SIG Meeting Notes


   Wednesday, February 29

      9:00  Opening Remarks -- BBN - Hinden
      9:10  SPF routing -- BBN - Seamonson
      9:35  Multiple Constraint Routing -- SRI - Shacham
      10:00 FACC Multinet Gateway Routing -- FACC - Cook
      10:30 Break
      11:00 Metanet Gateway -- SRI - Denny
      11:20 Address Mapping and Translation -- UCL - Crowcroft
      11:40 Design of the FACC Multinet Gateway -- FACC - Cook
      12:00 Lunch
      1:30  SAC Gateway -- SRI - Su/Lewis
      2:00  EGP -- Linkabit - Mills
      2:30  Congestion Control -- FACC - Nagle
      3:00  Break
      3:30  A Gateway Congestion Control Policy--NW Systems - Niznik
      4:00  Discussion

NOTES ON THE MEETING

   The MIT C Gateway -- MIT - Martin

      Postel:  A description of the gateway implemented at MIT.  The
      gateway was first developed by Noel Chiappa.  It is written in C.
      The MIT environment has 32 internal networks which are treated as
      subnets of the MITNET on the Internet.  The MIT gateways then do
      subnet routing in their interior protocol.  The subnet routing
      scheme is similar to GGP.  Liza has added an EGP implementation to
      this gateway.

      Muuss:

      Campus network/project Athena
      Dynamic routing
      Congestion control - grad student
                      +---------------+---+
       Class A net  : | 18|subnet|res|host|
                      +---------------+---+

      "Bridges" forward between subnets.

      Campus Network and Project Athena 65 VAX 750s, 200 IBM PCs.

      Hosts: Now = 400, 1986 = 3,000, 1990 = 10,000

      Subnets: Now = 42, 1985 = 60, 1990 = 200, (4 subnets/building)

      Protocols: Internet, DECnet, Chaosnet


Hinden, Postel, Muuss, & Reynolds                               [Page 2]



RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      FiberOptic spine between campus buildings.

      MIT gateways:

         11/03s and 11/23s
         68000 on Abus
         6800 on Multibus (Bridge communications)

         MIT C gateway -
         Runs under MOS, bridge OS, homegrown OS. Multiple protocols,
         multiple interfaces.

         11/03 - 100 packets/sec.
         11/23 - 180 packets/sec.

         GGP - Gw/Gw
         EGP - Exterior Gw
         IGP - Interior Gw

         EGP:  Autonomous systems

         EGP:
           Neighbor acquisition
           Hello/I heard you
           Net reachability poll
           Net reachability message

      MIT IGP:

         IP header on EGP protocol
         Dest: net number, subnet number, 0, 0377 (broadcast address)

      IGP header:

         Autonomous system number
         Sequence number
         Tasks:
             Propagate exterior and subnet routing.

      Packets
         Ext route request, and update Routing server
             Default gateway
             Exceptional gateways
             Nets reached

      MIT - Gw broadcasts initial routings when it comes up, and again
      on each change, net is flooded on each change several times. Each
      bridge can ask for help.


Hinden, Postel, Muuss, & Reynolds                               [Page 3]



RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      Future:  Wideband net gateway from BBN will also sit on net  18,
      and an MIT routing server to acquire routing information. Trick -
      BBN-Gw will be on an Ethernet, and a modified ARP will be used by
      the bridges to "fool" the BBN gateway into acquiring the routes.

      Subnet Routing - inspired by PUP and CHAOS
         Neighbor Bridge
           Net I/F
           Bridge address
           Latest seq number
           Aging value
         Route to subnet
           Distance

         Packets
           Request
           I'm up

             Route update
               Distance vector (256 bytes)
                       0 - Direct
                       1 -127 - hop count
                       128-255 - "Interface used for next hop" to subnet
                                 and hop count
                       255 - Unreachable

      Problem -
         Many neighbors --> too much time and traffic needed for
      processing.
      
         3 level addressing and routing strategy
         Ext Gw:
           Routing server
           Default Gw
         Subnet routing
           Small but rich subnet routing updates.

   The Butterfly Gateway -- BBN - Hinden

      Postel:  A description of the butterfly hardware and a discussion
      of the plans for the new gateway software to be implemented on it.
      The butterfly machine is a multiprocessor (MC68000's)
      interconnected with a funny switch.  The new software will
      incorporate the so called "Shortest Path First" or SPF routing
      algorithm.





Hinden, Postel, Muuss, & Reynolds                               [Page 4]



RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      Muuss:

      Replacement for existing 30 PDP-11 "core" gateways.
      Problems to be solved.

         o  Replace GGP
              - Routing updates filling up
              - Neighbor probes (N**2)
              - Few buffers

         o  Present GGP updates only hold 70 net numbers, repacking
            data will increase that to approximately 100 nets, but
            this is just short term.

      Features of Butterfly -
         o  1000's of nets
         o  Partitioned nets
         o  Type of service routing, access control
         o  Flow control
         o  Large and small gateway configurations

      New functions -
         o  Routing
         o  Neighbor discovery
         o  Reduce neighbor pinging
         o  Access/departure model
         o  Connect gateways with point-to-point lines

      Routing -
         o  SPF - shortest path first
         o  Gateway based routing (opposed to network routing)
         o  Routing updates
              Gw ID
              <nets directly connected>
              <neighbor, distance>
         o  Updates flooded to other gateways

      Next-door - Neighbors
         o  Neighbor gateways closest to gateway
         o  Ping next-door-neighbors only
         o  For up/down acquisition, partition into rings.  Reduces
            pinging.
      
      Access/departure model
      
          First Gw (entrance) picks exit gateway




Hinden, Postel, Muuss, & Reynolds                               [Page 5]



RFC 898                                                       April 1984
Gateway SIG Meeting Notes


          First Gw adds Gw - Gw header
      
      Butterfly gateway

          Processor nodes and switch nodes
         
          4-legged switch nodes, decision is simply UP or DOWN.  2
         inputs
          and 2 outputs.

          Processor:  MC 68000
          Memory management Unit
          Processor node controller - 2901 bit slice
          PVC is the memory controller.

         Butterfly -
          32 M bps/path
          Bandwith:   approximately N - speed
          Size:       approximately N/2   log  N 2

         Butterfly will support multibus interface; 1822, HDLC,
         Ethernet, Ring

      Terminal and load device will be a personal computer

      Small Gw for ARPA is approximately $20K

      New Gw processor structure

      Buffer Management
        o   Scatter/gather buffers minimum size and extensions
        o   Buffer pool on processors with I/O
        o   Primary and secondary collections per device
             ==>  guaranteed minimum service per device
                  (implemented w/counts)

   The EGP C Gateway -- ISI - Kirton

      Postel:  A user process was installed in Berkeley 4.2 Unix to do
      EGP protocol functions leaving the normal router kernel function
      in charge of forwarding datagrams.  The EGP user process may do
      system calls to update the kernel routing data.  Based on the work
      of Liza Martin.







Hinden, Postel, Muuss, & Reynolds                               [Page 6]



RFC 898                                                       April 1984
Gateway SIG Meeting Notes


      Muuss:

      EGP under 4.2

      Elimination of nonrouting gateways

      Design -
          Forwarding done in kernel
          Kernel does not send redirects
          EGP user process for route updates
          Written in C
          EGP based on Liza Martin's code

      Routing Tables
        o   Kernel
        o   EGP Process

      EGP Process Table -
        o   External updates
        o   Internal information

      Facilities -

         Configuration file-
             o   Trusted neighbors
             o   Internal non - routing gateways

         Acquisition -
           o   Predetermined number of core gateways are EGP'd to
           o   Only accept from trusted neighbors
           o   Cannot acquire neighbors indirectly, for now

         Unix Interfaces -
           Reuse IP socket (problem with protocol number)
           Listening to ICMP for redirects
           System calls for -
             o   Route updates
             o   I/F config reading
             o   I/F status check

         Performance -
             o   60 ms/packet pair (CPU time)
             o   Typically 1% of CPU for 1 minute polling

         Protocol function going
         Routing updates being implemented

         Should be all going in April.


Hinden, Postel, Muuss, & Reynolds                               [Page 7]



RFC 898                                                       April 1984
Gateway SIG Meeting Notes


   The BRL Gateway -- BRL - Natalie

      Postel:  This was a description of the BRL dumb gateway.  More
      interesting was the description of the BRL complex and the
      inteconnections between machines.  The gateway is written in C
      (and derived from the MIT C-Gateway) and based on a simple
      multiprocess operating system called LOS.

      Muuss:

      BRL history
      
      LOS design
        Message passing
        Memory Management
        No copying of data, buffer size

   The CMU Gateway -- CMU - Accetta

      Postel:  This was a description of the CMU dumb gateway.

      Muuss:

      History -
        o   "Logical-Host" multiplexor (March 81)
        o   Gateway (Oct 82) remote debugger and monitor
        o   Router (Oct 83)
              - Modular device and protocol support
              - Stub IP dynamic routing
              - Local inter-network cable routing.
        o   Written in "C"

      Uses low memory for buffers (maximum 32K)!
        (autoboot of 3M bps Ethernet)
      Auto-configuration of devices
      Individual stack contents
      Round-robin scheduler
      Dynamic memory allocation

      Device driver
        Network interfaces
        Auxiliary support devices

      Does IP, ICMP, UDP

         Splicing through of PUP and CHAOS on chaos net, uses ARP.

         Configuration testing protocol (as in Ethernet Spec).


Hinden, Postel, Muuss, & Reynolds                               [Page 8]