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+Network Working Group D. Piscitello
+Request for Comments: 1526 Bellcore
+Category: Informational September 1993
+
+
+ Assignment of System Identifiers for TUBA/CLNP Hosts
+
+Status of this Memo
+
+ This memo provides information for the Internet community. It does
+ not specify an Internet standard. Distribution of this memo is
+ unlimited.
+
+Abstract
+
+ This document describes conventions whereby the system identifier
+ portion of an RFC 1237 style NSAP address may be guaranteed
+ uniqueness within a routing domain for the purpose of
+ autoconfiguration in TUBA/CLNP internets. The mechanism is extensible
+ and can provide a basis for assigning system identifiers in a
+ globally unique fashion.
+
+Introduction
+
+ This memo specifies methods for assigning a 6 octet system identifier
+ portion of the OSI NSAP address formats described in "Guidelines for
+ OSI NSAP Allocation in the Internet" [1], in a fashion that ensures
+ that the ID is unique within a routing domain. It also recommends
+ methods for assigning system identifiers having lengths other than 6
+ octets. The 6 octet system identifiers recommended in this RFC are
+ assigned from 2 globally administered spaces (IEEE 802 or "Ethernet",
+ and IP numbers, administered by the Internet Assigned Numbers
+ Authority, IANA).
+
+ At this time, the primary purpose for assuring uniqueness of system
+ identifiers is to aid in autoconfiguration of NSAP addresses in
+ TUBA/CLNP internets [2]. The guidelines in this paper also establish
+ an initial framework within which globally unique system identifiers,
+ also called endpoint identifiers, may be assigned.
+
+Acknowledgments
+
+ Many thanks to Radia Perlman, Allison Mankin, and Ross Callon of for
+ their insights and assistance. Thanks also to the Ethernet connector
+ to my MAC, which conveniently and quite inobtrusively fell out,
+ enabling me to get an entire day's worth of work done without email
+ interruptions.
+
+
+
+
+Piscitello [Page 1]
+
+RFC 1526 System Identifiers for TUBA September 1993
+
+
+1. Background
+
+ The general format of OSI network service access point (NSAP)
+ addresses is illustrated in Figure 1.
+
+ _______________________________________________
+ |____IDP_____|_______________DSP______________|
+ |__AFI_|_IDI_|_____HO-DSP______|___ID___|_SEL_|
+
+ IDP Initial Domain Part
+ AFI Authority and Format Identifier
+ IDI Initial Domain Identifier
+ DSP Domain Specific Part
+ HO-DSP High-order DSP
+ ID System Identifier
+ SEL NSAP Selector
+
+ Figure 1: OSI NSAP Address Structure.
+
+ The recommended encoding and allocation of NSAP addresses in the
+ Internet is specified in RFC 1237. RFC 1237 makes the following
+ statements regarding the system identifier (ID) field of the NSAPA:
+
+ 1. the ID field may be from one to eight octets in length
+
+ 2. the ID must have a single known length in any particular
+ routing domain
+
+ 3. the ID field must be unique within an area for ESs and
+ level 1 ISs, and unique within the routing domain for level
+ 2 ISs.
+
+ 4. the ID field is assumed to be flat
+
+ RFC 1237 further indicates that, within a routing domain that
+ conforms to the OSI intradomain routing protocol [3] the lower-order
+ octets of the NSAP should be structured as the ID and SEL fields
+ shown in Figure 1 to take full advantage of intradomain IS-IS
+ routing. (End systems with addresses which do not conform may require
+ additional manual configuration and be subject to inferior routing
+ performance.)
+
+ Both GOSIP Version 2 (under DFI-80h, see Figure 2a) and ANSI DCC NSAP
+ addressing (Figure 2b) define a common DSP structure in which the
+ system identifier is assumed to be a fixed length of 6 octets.
+
+
+
+
+
+
+Piscitello [Page 2]
+
+RFC 1526 System Identifiers for TUBA September 1993
+
+
+ _______________
+ |<--__IDP_-->_|___________________________________
+ |AFI_|__IDI___|___________<--_DSP_-->____________|
+ |_47_|__0005__|DFI_|AA_|Rsvd_|_RD_|Area_|ID_|Sel_|
+ octets |_1__|___2____|_1__|_3_|__2__|_2__|_2___|_6_|_1__|
+
+ Figure 2 (a): GOSIP Version 2 NSAP structure.
+ ______________
+ |<--_IDP_-->_|_____________________________________
+ |AFI_|__IDI__|____________<--_DSP_-->_____________|
+ |_39_|__840__|DFI_|_ORG_|Rsvd_|RD_|Area_|_ID_|Sel_|
+ octets |_1__|___2___|_1__|__3__|_2___|_2_|__2__|_6__|_1__|
+
+ IDP Initial Domain Part
+ AFI Authority and Format Identifier
+ IDI Initial Domain Identifier
+ DSP Domain Specific Part
+ DFI DSP Format Identifier
+ ORG Organization Name (numeric form)
+ Rsvd Reserved
+ RD Routing Domain Identifier
+ Area Area Identifier
+ ID System Identifier
+ SEL NSAP Selector
+
+
+ Figure 2(b): ANSI NSAP address format for DCC=840
+
+2. Autoconfiguration
+
+ There are provisions in OSI for the autoconfiguration of area
+ addresses. OSI end systems may learn their area addresses
+ automatically by observing area address identified in the IS-Hello
+ packets transmitted by routers using the ISO 9542 End System to
+ Intermediate System Routing Protocol, and may then insert their own
+ system identifier. (In particular, RFC 1237 explains that when the ID
+ portion of the address is assigned using IEEE style 48-bit
+ identifiers, an end system can reconfigure its entire NSAP address
+ automatically without the need for manual intervention.) End systems
+ that have not been pre-configured with an NSAPA may also request an
+ address from an intermediate system their area using [5].
+
+2.1 Autoconfiguration and 48-bit addresses
+
+ There is a general misassumption that the 6-octet system identifier
+ must be a 48-bit IEEE assigned (ethernet) address. Generally
+ speaking, autoconfiguration does not rely on the use of a 48-bit
+ ethernet style address; any system identifier that is globally
+
+
+
+Piscitello [Page 3]
+
+RFC 1526 System Identifiers for TUBA September 1993
+
+
+ administered and is unique will do. The use of 48-bit/6 octet system
+ identifiers is "convenient...because it is the same length as an 802
+ address", but more importantly, choice of a single, uniform ID length
+ allows for "efficient packet forwarding", since routers won't have to
+ make on the fly decisions about ID length (see [6], pages 156-157).
+ Still, it is not a requirement that system identifiers be 6 octets to
+ operate the the IS-IS protocol, and IS-IS allows for the use of IDs
+ with lengths from 1 to 8 octets.
+
+3. System Identifiers for TUBA/CLNP
+
+ Autoconfiguration is a desirable feature for TUBA/CLNP, and is viewed
+ by some as "essential if a network is to scale to a truly large size"
+ [6].
+
+ For this purpose, and to accommodate communities who do not wish to
+ use ethernet style addresses, a generalized format that satisfies the
+ following criteria is desired:
+
+ o the format is compatible with installed end systems
+ complying to RFC 1237
+
+ o the format accommodates 6 octet, globally unique system
+ identifiers that do not come from the ethernet address space
+
+ o the format accommodates globally unique system identifiers
+ having lengths other than 6 octets
+
+ The format and encoding of a globally unique system identifier that
+ meets these requirements is illustrated in Figure 3:
+
+ Octet 1 Octet 2 Octet 3 ... Octet LLL-1 Octet LLLL
+ +-----------+-----------+-----------+- ...-+-----------+-----------+
+ | xxxx TTGM | xxxx xxxx | xxxx xxxx | | xxxx xxxx | xxxx xxxx |
+ +-----------+-----------+-----------+- ...-+-----------+-----------+
+
+ Figure 3. General format of the system identifier
+
+3.1 IEEE 802 Form of System Identifier
+
+ The format is compatible with globally assigned IEEE 802 addresses,
+ since it carefully preserves the semantics of the global/local and
+ group/individual bits. Octet 1 identifies 2 qualifier bits, G and M,
+ and a subtype (TT) field whose semantics are associated with the
+ qualifier bits. When a globally assigned IEEE 802 address is used as
+ a system identifier, the qualifier bit M, representing the
+ multicast/unicast bit, must always be set to zero to denote a unicast
+ address. The qualifier bit G may be either 0 or 1, depending on
+
+
+
+Piscitello [Page 4]
+
+RFC 1526 System Identifiers for TUBA September 1993
+
+
+ whether the individual address is globally or locally assigned. In
+ these circumstances, the subtype bits are "don't care", and the
+ system identifier shall be interpreted as a 48-bit, globally unique
+ identifier assigned from the IEEE 802 committee (an ethernet
+ address). The remaining bits in octet 1, together with octets 2 and
+ 3 are the vendor code or OUI (organizationally unique identifier), as
+ illustrated in Figure 4. The ID is encoded in IEEE 802 canonical
+ form (low order bit of low order hex digit of leftmost octet is the
+ first bit transmitted).
+
+ Octet 1 Octet 2 Octet 3 Octet 4 Octet 5 Octet 6
++-----------+-----------+-----------+-----------+-----------+-----------+
+| VVVV VV00 | VVVV VVVV | VVVV VVVV | SSSS SSSS | SSSS SSSS | SSSS SSSS |
++-----------+-----------+-----------+-----------+-----------+-----------+
+
+|------------vendor code -----------|--------station code---------------|
+
+ Figure 4. IEEE 802 form of system identifier
+
+4. Embedded IP Address as System Identifier
+
+ To distinguish 48-bit IEEE 802 addresses used as system identifiers
+ from other forms of globally admininistered system identifiers, the
+ qualifer bit M shall be set to 1. The correct interpretation of the M
+ bit set to 1 should be, "this can't be an IEEE 802 multicast address,
+ since use of multicast addresses is by convention illegal, so it must
+ be some other form of system identifier". The subtype (TT) bits
+ illustrated in Figure 3 thus become relevant.
+
+ When the subtype bits (TT) are set to a value of 0, the system
+ identifier contains an embedded IP address. The remainder of the 48-
+ bit system identifier is encoded as follows. The remaining nibble in
+ octet 1 shall be set to zero. Octet 2 is reserved and shall be set
+ to a pre-assigned value (see Figure 5). Octets 3 through 6 shall
+ contain a valid IP address, assigned by IANA. Each octet of the IP
+ address is encoded in binary, in internet canonical form, i.e., the
+ leftmost bit of the network number first.
+
+ Octet 1 Octet 2 Octet 3 Octet 4 Octet 5 Octet 6
++-----------+-----------+-----------+-----------+-----------+-----------+
+| 0000 0001 | 1010 1010 | aaaa aaaa | bbbb bbbb | cccc cccc | dddd dddd |
++-----------+-----------+-----------+-----------+-----------+-----------+
+
+|-len&Type--|--reserved-|---------IP address----------------------------|
+
+ Figure 5. Embedded IP address as system identifier
+
+
+
+
+
+Piscitello [Page 5]
+
+RFC 1526 System Identifiers for TUBA September 1993
+
+
+ As an example, the host "eve.bellcore.com = 128.96.90.55" could retain
+ its IP address as a system identifier in a TUBA/CLNP network. The
+ encoded ID is illustrated in Figure 6.
+
+
+ Octet 1 Octet 2 Octet 3 Octet 4 Octet 5 Octet 6
++-----------+-----------+-----------+-----------+-----------+-----------+
+| 0000 0001 | 1010 1010 | 1000 0000 | 0110 0000 | 0101 1010 | 0011 0111 |
++-----------+-----------+-----------+-----------+-----------+-----------+
+
+|-len&Type--|--reserved-|---------IP address----------------------------|
+
+ Figure 6. Example of IP address encoded as ID
+
+H 2 "Other forms of System Identifiers"
+
+ To allow for the future definition of additional 6-octet system
+ identifiers, the remaining subtype values are reserved.
+
+ It is also possible to identify system identifiers with lengths other
+ than 6 octets. Communities who wish to use 8 octet identifiers (for
+ example, embedded E.164 international numbers for the ISDN ERA) must
+ use a GOSIP/ANSI DSP format that allows for the specification of 2
+ additional octets in the ID field, perhaps at the expense of the
+ "Rsvd" fields; this document recommends that a separate Domain Format
+ Indicator value be assigned for such purposes; i.e., a DFI value that
+ is interpreted as saying, among other things, "the system identifier
+ encoded in this DSP is 64-bits/8 octets. The resulting ANSI/GOSIP DSP
+ formats under such circumstances are illustrated in Figure 7:
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Piscitello [Page 6]
+
+RFC 1526 System Identifiers for TUBA September 1993
+
+
+ ______________
+ |<--_IDP_-->_|______________________________
+ |AFI_|__IDI__|____________<--_DSP_-->_______|
+ |_39_|__840__|DFI_|_ORG_|RD_|Area_|_ID_|Sel_|
+ octets |_1__|___2___|_1__|__3__|_2_|__2__|_8__|_1__|
+
+ Figure 7a: ANSI NSAP address format for DCC=840, DFI=foo
+
+ _______________
+ |<--__IDP_-->_|___________________________________
+ |AFI_|__IDI___|___________<--_DSP_-->____________|
+ |_47_|__0005__|DFI_|AA_|_RD_|Area_|ID_|Sel_|
+ octets |_1__|___2____|_1__|_3_|_2__|_2___|_8_|_1__|
+
+ IDP Initial Domain Part
+ AFI Authority and Format Identifier
+ IDI Initial Domain Identifier
+ DSP Domain Specific Part
+ DFI DSP Format Identifier
+ AA Administrative Authority
+ RD Routing Domain Identifier
+ Area Area Identifier
+ ID System Identifier
+ SEL NSAP Selector
+
+ Figure 7b: GOSIP Version 2 NSAP structure, DFI=bar
+
+ Similar address engineering can be applied for those communities who
+ wish to have shorter system identifiers; have another DFI assigned,
+ and expand the reserved field.
+
+5. Conclusions
+
+ This proposal should debunk the "if it's 48-bits, it's gotta be an
+ ethernet address" myth. It demonstrates how IP addresses may be
+ encoded within the 48-bit system identifier field in a compatible
+ fashion with IEEE 802 addresses, and offers guidelines for those who
+ wish to use system identifiers other than those enumerated here.
+
+
+
+
+
+
+
+
+
+
+
+
+
+Piscitello [Page 7]
+
+RFC 1526 System Identifiers for TUBA September 1993
+
+
+6. References
+
+ [1] Callon, R., Gardner, E., and R. Colella, "Guidelines for OSI NSAP
+ Allocation in the Internet", RFC 1237, NIST, Mitre, DEC, June
+ 1991.
+
+ [2] Callon, R., "TCP and UDP with Bigger Addresses (TUBA), A Simple
+ Proposal for Internet Addressing and Routing", RFC 1347, DEC,
+ June 1992.
+
+ [3] ISO, "Intradomain routing protocol for use in conjunction with
+ ISO 8473, Protocol for providing the OSI connectionless network
+ service", ISO 10589.
+
+ [4] ISO, End-system and intermediate-system routing protocol for use
+ in conjunction with ISO 8473, Protocol for providing the OSI
+ connectionless network service, ISO 9542.
+
+ [5] ISO, "End-system and intermediate-system routing protocol for use
+ in conjunction with ISO 8473, Protocol for providing the OSI
+ connectionless network service. Amendment 1: Dynamic Discovery
+ of OSI NSAP Addresses End Systems", ISO 9542/DAM1.
+
+ [6] Perlman, R., "Interconnections: Bridges and Routers", Addison-
+ Wesley Publishers, Reading, MA. 1992.
+
+7. Security Considerations
+
+ Security issues are not discussed in this memo.
+
+8. Author's Address
+
+ David M. Piscitello
+ Bell Communications Research
+ NVC 1C322
+ 331 Newman Springs Road
+ Red Bank, NJ 07701
+
+ EMail: dave@mail.bellcore.com
+
+
+
+
+
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+Piscitello [Page 8]
+ \ No newline at end of file