📄 rfc1070.txt
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NSAP-Address Format
The OSI internetwork described here will form one routing domain,
with one form of NSAP address recognized by all level 1 routers in
this domain. Other address formats may be agreed upon in later
editions of this memo.
The address format to be used in this experiment is that specified in
RFC 1069. According to RFC 1069, the low-order portion of the Domain
Specific Part of the NSAP address may vary depending on the
conventions of the particular routing domain. For the purposes of
this experiment, we shall use the following address format:
Hagens, Hall, & Rose [Page 6]
RFC 1070 Experimental OSI Net February 1989
Address Format for EON
Octet Value Meaning
-------- ------------- ----------------------------------------
1 47 Authority and Format Identifier
2,3 00, 06 International Code Designator
4 3 Version Number
5,6 0 Global Area Number, see RFC 1069
7,8 RDN Routing Domain Number, assigned by IANA
9-11 0 Pad
12,13 0 LOC-AREA, see below
14,15 0 unused
16-19 A.B.C.D Internet address
20 NSAP Selector, assigned IANA
Note: It is our desire that the address format used by EON be
consistent with RFC 1069. To that end, the address format
proposed by this RFC may change as future editions of RFC 1069
become available.
The mapping between NSAP-addresses and SNPA-addresses (Internet
addreses) on the proposed IP subnet is straightforward. The SNPA-
address is embeded in the NSAP-address.
There are several ways in which the LOC-AREA field could be used.
(1) Assign local areas, administered by the Internet Assigned Numbers
Authority (IANA). The advantage of this is that it permits
experimentation with area routing. The disadvantage is that it
will require an additional directory service to map host names to
NSAP-addresses. We would like to use the existing domain name
servers to derive Internet addresses from names, and we would
like NSAP-addresses to be derivable from the Internet addresses
alone.
(2) Have one local area in the EON, with LOC-AREA value 0. This
would eliminate the problem of name-toNSAP-address binding, but
would not permit experimentation with area routing. It would
not, however preclude the use of areas later, for example, when
OSI directory services are widely available.
(3) Make the local area a simple function of the Internet address.
The advantage of this is that it would permit experimentation
with area addressing without requiring additional directory
services, but the areas derived would not be under the control of
the experimenters and may not correspond to anything useful or
meaningful for the purposes of this experiment.
We believe that initially, the preferred alternative is to use only
Hagens, Hall, & Rose [Page 7]
RFC 1070 Experimental OSI Net February 1989
zero-valued local areas. Later editions of this memo may contain
proposals for use of the local area field, when the IS-IS proposal is
more mature and perhaps when OSI directory services are in use among
experimenters.
The value of the high-order portion of the DSP will be set in
accordance with RFC 1069.
Other NSAP-Address Formats
PDUs carrying NSAP-addresses of other formats can be routed through
this domain. This is the job of the level 2 routers, described in
the IS-IS document.
Multicast Addresses on the IP Subnet
The ES-IS and IS-IS routing exchange protocols assume that broadcast
subnetworks support two multicast addresses: one for all ESs and the
other for all ISs. While one could obviate this issue by treating
the IP subnet as a general topology subnetwork or as a set of point-
to-point links, it is also desirable to treat the IP subnet as a
broadcast subnetwork for the purpose of testing those parts of an
implementation that run over broadcast subnets. A participating
implementor not having access to several local machines running the
OSI CLNL may test the protocols over the IP subnet as if the IP
subnet were a broadcast subnet.
The multicasting assumed by the OSI CLNL can be simulated by a small
sublayer lying between the OSI CLNL and the IP subnet layer. For the
purpose of this discussion, call this sublayer an SNAcP, a SubNetwork
Access Protocol, in OSI argot. In each system the SNAcP caches a
table of the Internet addresses of systems that it considers to be
reachable in one ISO 8473-hop over the IP subnet. These are called
"core" systems. In this sense, the use of the cache simulates a set
of links over which a system will send ISO configuration messages (ES
Hello, IS Hello, etc.) when it comes up. As a local matter, the
table of core systems may or may not expand during the system's
lifetime, in response to configuration messages from other core
systems.
On the outgoing path, the SNAcP accepts an ISO-gram and a parameter
indicating the intended use of this ISO-gram: send to a single
system, to all ESs, to all ISs, or to all systems. If the indended
destination is a single system, the ISO-gram is sent only to its
destination. Otherwise, the SNAcP makes a copy of the ISO-gram for
each of the SNPA-addresses in the cache, effecting a broadcast to all
participating systems. Before passing an ISO-gram to the IP subnet
layer, the SNAcP prepends an SNAcP header to each outgoing ISO-gram.
Hagens, Hall, & Rose [Page 8]
RFC 1070 Experimental OSI Net February 1989
This header will take the form:
SNAcP Header Format
Octet Value Meaning
--------------------------------------------------------
1 01 Version number
--------------------------------------------------------
2 Semantics of address:
00 Not a multicast address
01 All ESs
02 All ISs
03 Broadcast
--------------------------------------------------------
3,4 OSI checksum as defined in ISO 8473
The SNAcP header has three fields, a version number field, a
semantics field, and a checksum field. The version number will take
the value 01. The checksum field will take the two octet ISO
(Fletcher) checksum of the SNAcP header. The checksum algorithm is
described in ISO 8473.
The semantics field will take one of 4 values, indicating "all ESs",
"all ISs", "broadcast", or "not a multicast address". The value of
the semantics field is determined by a parameter passed to the SNAcP
by the calling OSI network entity. A participant in the experiment
may test the OSI network layer over a set of point-to-point links by
choosing not to use the multicast capabilities provided by the SNAcP
on the outgoing path.
On the incoming path, the SNAcP inspects the SNAcP header and decides
whether or not to accept the ISO-gram. If it accepts the ISO-gram,
the SNAcP removes the SNAcP header and passes the ISO-gram to the OSI
CLNL, otherwise, it discards the ISO-gram. The SNAcP will always
accept ISO-grams with SNAcP headers indicating "not a multicast
address" (value zero in the semantics field) and "broadcast" (value
03). Whether an SNAcP will accept ISO-grams for either of the two
multicast groups "all ESs" (value 1) and "all ISs" (value 2) will
depend on local configuration information. If the system on which
the SNAcP resides is configured as an end system, it will accept
ISO-grams destined for "all ESs" and if it is configured as an
intermediate system, it will accept ISO-grams destined for "all ISs".
A participant who is testing the OSI network layer over a set of
point-to-point links will accept ISO-grams according to these rules
as well.
Consideration was given to making the SNAcP extensible by making the
semantics and checksum fields variable-length parameters, in the
Hagens, Hall, & Rose [Page 9]
RFC 1070 Experimental OSI Net February 1989
manner of ISO 8473. We feel that the presence of a version number
provides sufficient extensibility.
Errors on the IP subnet
The IP subnet layer may receive ICMP messages and may pass error
indications to the SNAcP layer as a result of having received these
ICMP messages. It is assumed that in this context, the IP subnet
will handle ICMP messages in the same way that it handles them in any
other context. For example, upon receipt of an ICMP echo message,
the IP subnet will respond with an ICMP echo reply, and the SNAcP
need not be informed of the receipt of the ICMP echo message.
Certain ICMP messages such as source quench are likely to produce an
error indication to all layers using the IP subnet. The actions
taken by the SNAcP for these indications is purely a local matter,
however the following actions are suggested.
Suggested SNAcP Actions in Response to
ICMP-related Error Indications
ICMP message type Action taken by the SNAcP
-----------------------------------------------------------
Destination unreachable, If the remote address is present
Parameter problem, in the cache of core systems'
Time exceeded addresses, mark it unusable.
Inform network management.
-----------------------------------------------------------
Source quench If the remote address is present
in the cache of core systems'
addresses, mark the remote
address as unusable and set a
timer for a time after which
the address becomes usable
again.
Inform network management.
-----------------------------------------------------------
All others Ignored by the SNAcP layer.
To "inform network management" may mean to print a message on the
system console, to inform a local process, to increment a counter, to
write a message in a log file, or it may mean to do nothing.
The effect of marking a cached address as unusable is as follows.
When the SNAcP attempts to broadcast or multicast an ISO-gram,
addresses in the cache that are marked as unusable are ignored. When
the SNAcP attempts to send a non-multicast ISO-gram to an unusable
cached address, the SNAcP returns an error indication to the OSI
CLNL. In this way, when the OSI CLNL uses the SNAcP to simulate a
Hagens, Hall, & Rose [Page 10]
RFC 1070 Experimental OSI Net February 1989
set of point-to-point links, it is notified when a link fails, but
when the OSI CLNL uses the SNAcP to simulate a multicast subnet, it
is not notified when one system on the subnet goes down.
Use of UDP/IP in Lieu of IP
In addition to using IP directly, for testing purposes it may be
useful to support the OSI CLNL over the User Datagram Protocol (UDP).
This is because some implementors do not have direct access to IP,
but do have access to the UDP. For example, an implementor may have
an a binary license for an operating system that provides TCP/IP and
UDP/IP, but no direct access to IP. These implementors may
participate in a parallel experiment, called EON-UDP, by using UDP/IP
as a subnetwork instead of using the IP subnet. In this case, the
OSI NPDU (after fragmentation, if applicable) will be placed in the
data portion of a UDP datagram. UDP port 147 (decimal) has been
assigned for this purpose. These participants will place an SNAcP
between UDP and ISO 8473 rather than between IP and ISO 8473. In all
other respects, the EON-UDP experiment is identical to the EON
experiment.
Of course, network layers entities using the UDP/IP subnet will not
interoperate directly with network layers entities using the IP
subnet. The procedures proposed in this memo do not prevent an
implementor from building an EON to EON-UDP gateway, however the
issues related to building and routing to such a gateway are not
addressed in this memo. This memo simply proposes two distinct
parallel experiments for two groups of experimenters having different
resources.
The preferred method of experimentation is to use the IP subnet, in
other words, EON. The EON-UDP variant is intended for use only by
those who cannot participate in EON.
Dissemination of Topological Information and Host Names
The EON experiment simulates a logical topology that is not as
connected as the underlying logical topology offered by the Internet.
The topology of the IP subnet is, in effect, simulated by the SNAcP
layer in each of the core systems. Each of the core systems caches a
list of the other core systems in the EON. When a system boots, it
needs some initial list of the participating core systems. For this
reason, a list of core systems will be maintained by the IANA.
In addition, a list of all participating ESs will be maintained by
the IANA. This list is not necessary for the functioning of the EON
network layer. It is a convenience to the experimenters, and is
meant for use by application layer software or human users.
Hagens, Hall, & Rose [Page 11]
RFC 1070 Experimental OSI Net February 1989
Two pairs of lists are kept, one for the EON and one for EON-UDP.
core.EON This is a list of SNPA-addresses of those systems
that will be (logically) reachable via the IP subnet
in one ISO 8473-hop from any other core system. This
does not mean that systems in this file are gateways
or ISs. They may be ESs, ISs or both. A site may
participate as a core system before its address is
included in this file and distributed to other core
systems, but under these circumstances other core systems
will not know to send configuration messages (ESHs and
ISHs) to the new site when coming up or rebooting. The
SNPA-addresses in this file will be ASCII strings of
the form A.B.C.D, no more than one per line.
White space (tabs, blanks) will be optional before
A and after D. A pound-sign (#) will indicate that
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