As per Relevance of the word university, we have this rfc below:
Network Working Group R.
Request for Comments: 831 University College
December 1982
Backup Access to the European Side of
Robert
The purpose of this RFC is to focus discussion on
particular Internet problem: a backup path for
maintenance of the European sector of the Internet,
use when SATNET is partitioned. We propose
mechanism, based upon the Source Routing option of IP
to reach European Internet sites via the VAN
and UCL
This proposal is not intended as a standard at
time
Network Working Group R.
Request for Comments: 831 University College
December 1982
1.
During several previous SATNET meetings, it has
observed that it would be useful for BBN to be able
access the European side of SATNET indirectly via the
Gateway, when direct SATNET connectivity has been lost
This short paper proposes a possible approach to
"backup" access, using the source routing option of IP
Figure 1 illustrates the problem we wish to solve. The
host H is used for diagnosis and control of the
SIMP's S1 and S2 as well as the gateways B and G and the
TAC (not shown, but connected to G).
(partitioned
ARPANET/SATNET __ __
Gateway Simp ( \ \ ) Simp
____ ___( / / )____ ____
| B |__| S1 | \ \ | S2 |________| G |_____
|____| |____| / / |____| |____|
| ( \ \ ) |
| (__ / /__) _______|____
________|____ ( )
( ) ( )
( ARPANET ) ( UCL NET )
( ) ( )
(_____________) ( )
| | (_____________)
__|_ | VAN/ .
| H | | Public Data Nets .
|____| | _____________ .
Diagnostic | ( ) .
Host __|__ ( VANNET ) _.___
| VAN |* * (* * * * * * * * *)* * * * | |
| gw------(--- IP Tunnel -----)--------| U |
|_____|* * (* * * * * * * * *)* * * |_____|
VAN ( )
Gateway (_____________)
Figure 1. US/UK Connectivity with Partitioned
RFC 831 - 1 - [Braden
Network Working Group R.
Request for Comments: 831 University College
December 1982
VANgw is the VAN Gateway which encapsulates IP datagrams
X25 packets for transmission over VAN/PTT virtual circuits
The collection of these paths, called "IP tunnels" by UCL
is addressed from the Internet as a distinct network
VANNET
U is a UCL host, the Terminal Protocol Converter,
provides a path to UK X25 networks. However, to the
world U looks like a host on VANNET, so the path from U
UCLNET (shown dotted) does not appear to exist
Now suppose SATNET is partitioned between S1 and S2.
we wish host H to be able to exchange IP datagrams with S
via the "back door" path
H - Internet - VANgw - VANNET - U - UCLNET - G - S
There are some important rules in this game, however
(1) U may only be a host, not a gateway
This is because we do not want the Internet to
ALL its traffic (e.g. rsre traffic and UCL
that is required to use SATNET) via the IP Tunnel
So the VAN Gateway (VANgw) must not discover it
get to UCLNET through U
(2) To implement the back door path to S2, we
willing to have some special code in H and/or in U
but not in G, S2, or VANgw
Note: Jack Haverty is allowed to violate
assumption, though we doubt that he will want to
But we must stick to it
Given these constraints, we claim that the only
solution is to "mung" the headers of IP datagrams at UCL
Thus, when SATNET is partitioned
(1) The IP addresses of S2, G, and the UCL TAC
unreachable from all US gateways. Therefore, if
sends a packet addressed to one of
destinations, it will be discarded and an
unreachable message returned
RFC 831 - 2 - [Braden
Network Working Group R.
Request for Comments: 831 University College
December 1982
(2) Similarly, the IP address of H is unreachable
the UK side. Hence, if the XNET debugger in a
host emits a return packet addressed to H,
packet will be dropped
Therefore, the destination address of each packet from
must be changed in order to reach the UCL side of SATNET (S
or G), and the source address of each of these packets
be changed so that return packets can reach H. For
purpose, we introduce the Munger host M (see Figure 2).
(partitioned
BBN __ __
Gateway Simp ( \ \ ) Simp
____ ___( / / )____ ____
| B |__| S1 | \ \ | S2 |________| G |_____
|____| |____| / / |____| |____|
| ( \ \ ) |
| (__ / /__) _______|____
________|____ ( )
( ) ( )
( ARPANET ) ( UCL NET )
( ) ( )
(_____________) ( )
| | (_____________)
__|_ | |
| H | | Public Data Nets |
|____| | _______________ _|___
Diagnostic | ( ) | M1 |
Host __|__ ( ) |:::::|
| VAN |* * (* * * * * * * * * *) * * |:::::|
| gw------(--- IP Tunnel -----)------------| M2 |
|_____|* * (* * * * * * * * * *) * * |_____|
VAN ( VANNET )
Gateway (_______________) "
Munger
Figure 2. Introduction of Header Munger at
Host "M" (M1/M2) is mulit-homed, appearing as host M2
VANNET and as host M1 on UCLNET. Like host U (shown
Figure 1), host M2 is the end of an IP Tunnel
communicates with VANgw over an X25 virtual call
RFC 831 - 3 - [Braden
Network Working Group R.
Request for Comments: 831 University College
December 1982
Suppose for example that host H desiollege
December 1982
Suppose for example that host H desires to reach the
debugger in the SIMP S2. H must send its packets
destination address M1; these will be routed to M1 via
and the IP Tunnel. Host M will change the headers of
datagrams to contain source address M1 and destination S2.
S2 will return packets to M1, and M1 will change them
to M2->H packets and launch them back through the VANNET
H
How does M know how to change the headers
(1) M could respond to a range of M1 and M2 addresses
and have a fixed table of correspondence
(2) We propose instead to use the SOURCE ROUTING
in the datagrams. This assumes that H is able
build source-routed datagrams, and is not upset
the intermediate host in the route is not a gateway
If we further assume that the IP layers in G and S
can handle source and return routes, then the
is simple. M must contain the source
algorithm of a gateway, but otherwise act as
hosts (no routing updates, etc).
(3) Although G supports source routing, S2 and the
may not. In that case, S2 and the TAC will not
able to recognise the return route in a
packet and use it as a source route in packets
in reply
This possibility calls for additional complexity
M, a combination of (1) and (2):
* In the US -> UK direction, the
Routing option would be used
* In the reverse direction (UK -> US),
mapping of datagram addresses would
controlled by a table in M
RFC 831 - 4 - [Braden
Network Working Group R.
Request for Comments: 831 University College
December 1982
We suggest that M use source routing to get
from H to S2, and meanwhile build a "soft state
table showing this mapping. When a packet
from S2 without source routing, M would consult
soft state table to discover how to alter
addresses to reach H again. This would allow
one US host at a time to access a given SATNET host
but surely this is no restriction
In practice, M2 and U should have different IP tunnels
hence different DTE addresses. Since the caller pays
X25 charges, the IP Tunnel for U will normally be
only by UCL. On the other hand, the IP Tunnel to M2 will
opened from the US end. Since UCL has only one PSS line
this requires the use of separate X25 subaddresses. The
gateway must handle 14 digit X121 addresses, as well as 12
digit addresses
2.
Robert Cole of UCL has made major contributions to
contents of this paper. In particular, he suggested the
of the Source Routing option
RFC 831 - 5 - [Braden
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
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