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LinuxDig.com Request For Comments

RFC Number : 898

Title : Gateway special interest group meeting notes.


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







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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


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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.


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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.





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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


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




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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.







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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.


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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).


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RFC 898 April 1984
Gateway SIG Meeting Notes


IP Processing-

o Consistency checks
o Redirects does not forward misrouted packets
o Fragmentation - ICMP dest unreach If DF Set
o Access list for who can pass through

No GGP, no EGP, Uses known gateways

Ordinary devices and PDP-10 and PDP-20

The Wisconsin BITNET/CSNET Gateway -- UWisc - Solomon

Postel: This was a discussion of a mail relay between the
Internet and BITNET to be installed at Wisconsin.

Muuss:

WISC-IBM (192.5.2.24) will connect to BITNET

Mail gateway, BITNET uses RFC 822 headers!

LAN to X.25 Gateway -- Computer Gateways Inc. - Buhr

Postel: This was a description of a protocol translation device
between an X.25 world and the DATAPOINT ARCNET world.

Muuss:

ARCNET to X.25 Bridge

ARCNET - from Datapoint,
Baseband coax, 2.5 mbps
Token passing
Reserve/send/wait/ack protocol
RIM chip implements this

'The OSI models seem less clear than the Internet models, perhaps
because they are less well developed.'

Wraps the subnetwork in an enhanced subnetwork layer.

Every pair of subnetworks must be connected in this design - hence
a bridge not a gateway.

Bridge is a network layer RELAY.

ARCNET address is sent as X.25 data


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RFC 898 April 1984
Gateway SIG Meeting Notes


ISI-UCI Gateway -- UCI - Rose

Postel: This was a description of the UCI dumb gateway. This one
is made up of two hosts (VAX 750s) 50 miles apart. The VAXs are
connected via a 9.6 Kbs leased line. One is interfaced to the
ISI-NET (an Ethernet) and the other to UCIICS net (also an
Ethernet). The VAXs run Berkeley Unix 4.1. These VAXs run as
regular hosts too.

Muuss:

MTU is 512. Effective bandwidth of approximately 6000 baud over
9600 baud line.

FACC Gateway -- FACC - Holkenbrink

Postel: A description of a gateway designed by Ford. The gateway
is based on a MC68000 multiprocessor and a VME bus. An
interesting question that came up during this presentation was
'What is the least information a host (or gateway) must have when
it comes up, and how can it acquire the rest of what it needs to
go into full operation from the environment?'

Muuss:

Inter-segment Processor. M68000 CPU with various co-processors.
68000 IOPS, 1822, IOP Ethernet IOP. 1 cpu does IP, routing.
Multi-cpu version of MOS

Lincoln IP/ST Gateway -- LL - Forgie/Kantrowitz

Postel: This was a discussion of the design of the Lincoln
gateways used primarily in the WBCNET for speech transmission
research. This gateway uses special I/O interfaces to promote a
high packet processing rate. The gateway implements both the
regular IP, and the ST protocol which permits resource
reservations to minimize the variation in transmission delay.
These gateways can, of course, act as regular internet gateways,
and have achieved very good performance in terms of datagrams per
second.

Muuss:

Packet voice experiments, wideband SATNET. Concentrate traffic
from local nets to trunk net. Needed enough performance to load
WBSATNET. 11/44 and ACC IF11 (Z-80). T1 trunk protocol converter.
(voice T1 <--> datagram)



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RFC 898 April 1984
Gateway SIG Meeting Notes


IP problems -
o Congestion
o High packet header overhead
o No support for conference call

ST -
o Virtual circuit
o Know capacity in advance, schedule channel
o Abbreviated header

11/44 - 900 to 1000 pkts/sec.

Port processor:
Sync low speed: 600K bits/sec.
Packet processing: 500 pkts/sec. average
20-talker LPC voice loop, 28 data
bytes/pkt, 50% duty cycle
Data handling
4 pcm voice stream loop 64K bps
184 data bytes/pkt, 100% duty cycle

Dispatcher Requirements
o Timely do ST
o Utilize rest of circuit for IP
o Performance measurement

Reservations on the SATNET: Each host makes a reservation for
Nbytes of M messages every INTERVAL. Reservations are absolute.

ST and IP for each distant run = MPP multipurpose packets.

12,000 lines of C code in 11/44 portion.

Minimal Stub Gateways -- MITRE - Nabielsky

Postel: This was a more abstract discussion of how stub gateways
could interact and acquire information about the topology of the
Internet.

Muuss:

Ethernet stub to Internet
Inexpensive, single-band ISBC 186/51 Intel @ $3000
High performance. EGP?

128K bytes/board

The Internet forest


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RFC 898 April 1984
Gateway SIG Meeting Notes


Alternative to ARP using Multicast

SPF routing -- BBN - Seamonson

Postel: This was a fine presentation of the principles of the
'Shortest Path First' (SPF) routing procedures with some remarks
on how it is tailored to the Internet gateway situation. One
point that was impressed on me was that when using SPF in a set of
gateways (say, the core autonomous system) the procedure will do
routing to an 'exit' gateway. Somehow I had not thought about it
in those terms before, but (obviously) just as there is a source
and a destination IMP in the ARPANET there will be an entrance and
an exit gateway in an SPF autonomous system.

Muuss:

Features -
Metric, update procedures, path calculation, forwarding

Current GGP problems -
o Counting to infinity
o Not enough topology information in each Gw
o Updates potentially very large

SPF in ARPANET
o Single path (not optimal) - no split of flow
o Delay based, to minimize delay
o Global knowledge of connection topology and delays

Metric used -
o Delay, delay of each packet averaged
(queueing plus transmission plus propagation)
arrival-to-arrival time.
o Average delay on each trunk computed every 9.6 seconds.
Report large changes in delay, fast

Update procedure -
o Updates report delay to each neighbor
o Update triggered by topology change, significant delay
change, or 1 time/minute.
Decay of threshold to direct to send update
o Sequence numbers
o Flooding on all trunks sent out on all lines
o Receipt of echo is acknowledgement
o Retransmission
o Aging of information
o Updates are 2*n*l packet growth. n = number imps,
l = number lines


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RFC 898 April 1984
Gateway SIG Meeting Notes


- When lines goes up, rather than dumping routing
table,just waits one minute until all updates have
been heard.

Path calculation
o Dijkstras Algorithm

20
A _______________ F
/
3 / 1015
/
B/___5___D E
/ /
/ /
1 / /5
/ /
C /

1. A B(A, 3), D(A, 10), E(A, 15). F(A, 20)

2. A C(B, 4), D(B, 8), E(A, 15), F(A, 20)
|
B

4. A E(C, 9), F(A,20)
|
B
/
C D

5. A
|
B
|
C
/
E

Then tree is inverted into a 'go here to get to this destination.'

For Internet -

Similar algorithm, needs special packet header to
indicate 'exit' gateway to get to destination network.

Update procedure -
Neighbor interface, neighbors, and delay to neighbor.


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RFC 898 April 1984
Gateway SIG Meeting Notes


'Next door neighbors' for minimizing traffic.
Ability to package multiple updates in one average
explicit Acks.

Path calculation -
o Possible to build different trees based on type of
service.

Forwarding -
o Exit Gw
o Consistent databases are important.

Multiple Constraint Routing -- SRI - Shacham

Postel: This was a clear presentation of some of the consequences
of the idea of type of service routing. The level of complexity
of the routing procedure is determined to depend on how many
catagories of service there are and how many selections there are
in each catagory. A few examples were discussed including the
current type of service parameters of IP.

Muuss:

Both current and proposed ARPANET algorithms provide 'best' path
under single constraint (number of hops, delay).
Internet will have diverse characteristics, it would be nice to
consider more than one constraint.

o Determine a set of measures.
o Represent each measure as a single number.
o Determine range of values. (complexity 0(c**n) range of n)
o Define path measure as a function of measure of length.
sum (delay, cost)
min/capacity, length, security)

If just one cost is used, then SPF (or whatever) can be used for
each cost. However, under multiple constraints there is a more
difficult problem. e.g.: minimum delay with packet size of at
least 1000 bytes.

RUMC has been shown to be in the NP complete family.

RUMC needs bigger tables, more processing and routing overhead.
Its not awful for 2-choice TOS, like in IP.

Table size is random, we have to be prepared for the worst case.

Possible strategies: flood a 'search packet,' dropped when


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RFC 898 April 1984
Gateway SIG Meeting Notes


constraints are not met, see if it makes it though. Good only for
virtual circuit. Weighted sum (VC only) works only with some
probability.

TOS is needed for Internet, but the algorithms are costly.
Complexity for providing TOS IP style is not too high.

FACC Multinet Gateway Routing -- FACC - Cook

Postel: This approach considered hop count to be an inadequate
metric for routing decsions in a system of different types of
networks (e.g., Ethernets, ARPANETs, 2.4Kb lines). Delay was
selected as the metric to use. There are some interesting issues
in the measurement of delay for some types of networks. Also, the
design considers the use of multiple paths when they are avaiable,
and routing to provide connectivty between the parts of
partitioned networks.

Muuss:

Routing with a single constraint.
A network of gateways Access, Transport, or Dual networks.
Some networks are used as backbones between gateways only.

Routing updates
Variable length
Broadcast routing updates

Unitary ends - A - Gw - B - Rest
Routing for A is really just routing to B
Neighbor Gws, nets
Lots and lots of tables

Metanet Gateway -- SRI - Denny

Postel: This is a project to invent several new addressing
features for gateways. In particular, there is a scheme to use an
option much like the source route option to do multi-addressing of
IP datagrams. It seems as if the gateways that implement this
option will have to know which other gateways do and don't
implement it. Also, there was discussion of a gateway to a
network that is in radio silence, and how to keep TCP connections
going with hosts that can't talk. This project is also concerned
about network reconstitution, security, survivability, congestion
control, and supporting multimedia data (voice, bitmaps, etc.) in
applications. A gateway is being developed in ADA for a MC68000
machine (SUN), and the initial version of the gateway is to be up
in May 84.


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RFC 898 April 1984
Gateway SIG Meeting Notes


Muuss:

Navy internet
Multimedia mail and conf.
Radio silence (EMCON)
Security and Survivability.

EMCON - Causes special problems for EGP and IGP one way nonTCP
mail delivery. No Acks. Uses name screen to redirect mail to
special one-way mail catcher, who then forwards using ordinary
methods.

Security and survivability
Access control - 'capability' - 32/64 bit key which changes
frequently (every hour or so)

Reconstitution - Partitioning, coalescing, mobile host
Test and monitoring - HMP

Gateway target - 68000 in ADA. Telesoft compiler

Address Mapping and Translation -- UCL - Crowcroft

Postel: This was a discussion of some of the issues in
interconnecting networks of different types including the Internet
and networks in England such as the Universe network. The
Universe network is made up of Cambridge Rings at several sites
linked via a satellite channel.

Muuss:

ARPA - SATNET - NULLNET - UCLNET UNIVERSE Satellite, 3 UCL rings

SAM -
o IP switch to several 1822 hosts
o IP/universe mapper, overlays UCLNET on universe
o Mask and match
128. 11. code. host

Three types:

1. Direct: code --> subnet
2. Redirect: 2nd lookup (for multihoming)
3. Logical: Logical address into a table of universe
names.
Name lookups give addresses and routes.

IP tunnels through X.25


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RFC 898 April 1984
Gateway SIG Meeting Notes


BBN Van gateway PSS - IPSS -Telenet - for hosts that can't use
SATNET.

SAM does access control and multihoming. Clever Multihoming gives
host a second address and sends an ICMP/Redirect to force TCP
connection to go through a different route, but wind up at same
place!!!

Wrote EGP in ADA. It didn't help at all.

Design of the FACC Multinet Gateway -- FACC - Cook

Postel: This is a distributed multiprocessor machine using a
special bus network for the interprocessor communication. The
softaware is written in C. The gateways is in an early test
phase.

Muuss:

RADC program

Started with AUTODIN II, switched to DDN.
Small to large switching devices.
DoD uses of PDNs, and partitioned network problems.

Distributed processing architecture -
Parallel contention, 90M bps bus, 22 wires. Each node has cpu,
memory, optimal comm line. Wire - OR presentation of address,
contention happens each time bus becomes free, all requestors
put out type of msg, pri, and address. Reads back wire - OR of
result, and highest gwy wins, sorted by (pri, type, higher
addr).
Bus was originally designed for our FAA fail-soft application
Z-800l w/MMU. Not binary addressing, but unitary (base1)
One element resolved per bus transaction.
Boards may be plugged in while running.
Inherent parallelism in layered protocols.

Interface connector clues board to modem levels and date rate. Up
to 100K bps now, soon up to T1 rate.

Multiprocessor approach allows routing calculation to take place
out-of-band from the measurement of delay and traffic, and allows
use of more compute power for routing.

Mostly written in C, with some assembler. Multiprocessor
operating system, designed from scratch.



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RFC 898 April 1984
Gateway SIG Meeting Notes


SAC Gateway -- SRI - Su/Lewis

Postel: This was a presentation of the design for the gateways to
be used in the advanced SAC demo experiments on network
partitioning and reconstitution, and communication between
intermingiling mobile networks. Much of these demonstrations will
be done with packet radio units and networks. Some of the ideas
are to use a gateway-centered type of addressing and double
encapsulation (i.e., an extra IP header) to route datagrams.

Muuss:

Network dynamics due to component mobility or failure.
Mobile host, reconstitution, partitioning.
H/W: 11/23
S/W: Some 'C' gateway
OS: VMOS (SRI)

Gateway-centered addressing, rather than network.
Gw host instead of net.host.
Double encapsulation: additional IP header.
TCP uses addr as an ID, IP uses it as an ADDRESS (-> route)
Need to separate these dual uses of this address field.
Incremental Routing (next-hop indication)

EGP -- Linkabit - Mills

Postel: A presentation of the EGP design. EGP has three major
aspects, neighbor acquisition, neighbor reachability, and network
reachability. The autonomous system concept was discussed.

Muuss:

Background, Implementation, Experience, Disparaging Remarks

Design goals -
o Established demarcations
o Decouple implementations
o Confine routing loops
o Exchange reachability information
o Provide flow control for connectivity information
o Medium-term lifetime

Non goals Not trying to do these!
o Flexibility of topology
o Rapid response Very slow update




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RFC 898 April 1984
Gateway SIG Meeting Notes


o Adaptive routing
o Common routing metric No agreement at all
o Load sharing or splitting

'Good news travels fast and bad news travels forever.'
Not for routing, but only provides reachability

RFC827 initial mode, RFC888 stub protocol

Neighbor acquisition protocol
o 2-way shake
o Flow - rates
o Explicit acquisition/cause

Neighbor reachability protocol
o Periodic polling
o Parasitic information
o Reachability algorithm Network reachability
protocol
o Periodic pulling
o Remote information
o Direct and indirect neighbors
o Indirect internal and indirect external
neighbors
o Distance information

EGP neighbors do not need to peer with more than one
CORE gateway, but you may peer with anybody you wish.

Shortcomings -
o Slow reaction due polling
o Tree-structured routing constraint
- Rigid topology
- Administrative resistance to odering
- Lack of adaptive connectivity
o Neighbor acquisition incomplete.

Loops between autonomous systems will last a long
time, and are a real no-no.

System models -
o 'Appropriate first hop' criterion
- Not useful for implementation
- Requires global information
- Inadequate for verification
o Graph models
- N-graph shows net connectivity
- T-graph shows system connectivity


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RFC 898 April 1984
Gateway SIG Meeting Notes


- T-acycloc criterion insures loop-free
o Derived features
- Induces spanning tree

N-graph

G1
A_______________B
/ /
G2 / G3 G4 / G5
/ /
C------D E-----F G6

AS1 = G2, G3, G6 A B
AS2 = G1
AS3 = G4, G5 AS1 ----- AS2 ----- AS3

T-graph

Test: to ensure that there are no cycles

Spanning subtree

Specification effort - Status report State machine designed

Remaining issues -
o Remove extra hop in core system
o Expand tables
o Test backdoor 'GGP'
o Resolve specification issues
o Resolve full gateway configuration
- Back door connectivity guidance
- can only advertise 1 path at a time.
- APF rule guidancee
- Self organization issues
o Implement and distribute for operational systems.

Congestion Control -- FACC - Nagle

Postel: This was a discussion of the situation leading to the
ideas presented in RFC 896, and how the policies described there
improved overall performance.








Hinden, Postel, Muuss, & Reynolds [Page 20]



RFC 898 April 1984
Gateway SIG Meeting Notes


Muuss:

First principle of congestion control:

DON'T DROP PACKETS (unless absolutely necessary)

Second principle:

Hosts must behave themselves (or else)

Enemies list -

1. TOPS-20 TCP from DEC
2. VAX/UNIX 4.2 from Berkeley

Third principle:

Memory won't help (beyond a certain point).

The small packet problem: Big packets are good, small are bad
(big = 576).

Suggested fix: Rule: When the user writes to TCP, initiate a send
only if there are NO outstanding packets on the connection. [good
for TELNET, at least] (or if you fill a segment). No change when
Acks come back. Assumption is that there is a pipe-like buffer
between the user and the TCP.

The source quench problem Rule: When a TCP gets an ICMP Source
Quench, it must reduce the number of outstanding datagrams on
relevant TCP connections.

Rule: When a gateway nears overload, before starting to drop
packets, send a Source Quench.

Node capacity: Each node ought to have one buffer for each TCP
connection, plus some for overload.

Both fixes really need to be done together, although the first one
is often helpful by itself. Side effect: FTPs start off 'slowly,'
until the first Ack comes back Dave Mills thinks this will
increase the mean delay for medium-size interactions. This
probably will not work so well for SATNET.

Problems about propagation time of links biasing the validity of
this result!!




Hinden, Postel, Muuss, & Reynolds [Page 21]



RFC 898 April 1984
Gateway SIG Meeting Notes


A Gateway Congestion Control Policy--NW Systems - Niznik

Postel: This talk was (for Postel) hard to follow. There were a
number of references to well known results in queuing theory etc,
but I could not follow how they were being used.

Muuss:

Replacements for IMP SPF
Topological observations
Nodal congestion control policy
GMD - control application [from German network]
RPN - relational Petri net
DCT - dynamic congestion table
NCCP performance evaluation
Planned GCCP: Gateway congestion control policy

Lots of diagrams and figures.

Better throughput than SPF, but somewhat higher delay.

Cubic structure of table.

DISCUSSION (Postel's personal comments)

There was very little organized discussion during the meeting and
not really very much question and answer interaction during the
presentation. There was a lot of discussion during the breaks,
and at lunch time, and at the end of each day.

Some things that occured to me during the meeting that may have
been triggered by something someone said (or maybe by the view out
the window):

Don't design a protocol where you expect to get a lot of
messages from a lot of sources at the same time. For example,
don't ask all the hosts on an Ethernet to send you an ack to a
broadcast packet.

Has anyone worked out in detail the routing traffic costs for
the GGP vs the SPF procedures for the actual case of the
Internet?

How will the fact that thinking of the routing in the core
autonomous system is cast in terms of an entry and an exit
gateway effect other things? Will there be special




Hinden, Postel, Muuss, & Reynolds [Page 22]



RFC 898 April 1984
Gateway SIG Meeting Notes


arrangements between the entry and exit gateway? Will an
autonomous system become a circuit switch connecting pairs of
entry/exit gateways?

Is TOS routing worth the cost?

Should we allow (as a new type of ICMP message) redirects to
Gateways?

Does making memory larger ever hurt? If a gateway's memory is
full of inappropriately retransmitted TCP segments would it be
better if there were less memory?

Is there something reasonable to do with source quench at the
TCP? Re: RFC-896.

If there are links (or networks) of vastly differing delay and
thruput characteristics what impact would an IP level load
splitting (say by gateways) have on TCP connections (some of
the segments of the connection go one path and others go a
different path)?

Are any problems avoided (either way) by using double IP
headers vs a 'source route like' IP option to separate the IP
level addressing and routing function from the TCP level
end-point naming function of the IP addresses.

What bad things could happen from the proposed IP
multidestination routing option?





















Hinden, Postel, Muuss, & Reynolds [Page 23]



RFC 898 April 1984
Gateway SIG Meeting Notes


MEETING ATTENDEES

Mike Accetta - CMU
R. Buhr - Canada
J. Noel Chiappa - MIT
Paul Cook - Ford
Jon Crowcroft - UCL
Barbara Denny - SRI
Jim Forgie - LL
Steve Groff - BBN
Phill Gross - Linkabit
Kjell Hermansen - NTA
Robert Hinden - BBN
Patrick Holkenbrink - FACC
Ruth Hough - AIRINC
Willie Kantrowitz - LL
Paul Kirton -ISI
Mark Lewis -SRI
Liza Martin - MIT
Doug Miller - MITRE
Dave Mills - Linkabit
Mike Muuss - BRL
Jose Nabielsky - MITRE
Ron Natalie - BRL
John Nagle - Ford
Carol Niznick NW Systems
Jon Postel - ISI
Joyce Reynolds -ISI
Marshall Rose - UCI
Joe Sciortino - AIRINC
Linda Seamonson - BBN
Nachum Shacham - SRI
Alan Sheltzer - UCLA
Marvin Solomon - WISC
Zaw-Sing Su - SRI
Mitch Tasman - BBN














Hinden, Postel, Muuss, & Reynolds [Page 24]




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