156 lines
5.2 KiB
Plaintext
156 lines
5.2 KiB
Plaintext
.NC "NSAP Addresses & Routing"
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.sh 1 "OSI Address Formats"
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.pp
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ARGO supports an ISO address family, AF_ISO, in addition to the
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DoD Internet address family, AF_INET.
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Addresses in the family AF_ISO
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take the form described by ISO 8348/DAD2, which is an addendum to the
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OSI network service standard that describes network layer addressing.
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.sh 2 "ISO 8348/DAD2 Tutorial"
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.pp
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.\" FIGURE
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.\".so figs/osi_addr.nr
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.so figs/addrfmt.nr
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.CF
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shows the
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format of an OSI NSAP-address.
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The address has two major parts: the initial domain part
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(IDP) and the domain specific part (DSP). The IDP is further divided into
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two parts: the authority and format identifier (AFI) and the
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initial domain identifier (IDI). The AFI specifies the format of the
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IDI, the authority responsible for allocating values of the IDI, and
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the syntax of the DSP. The IDI specifies the network addressing domain
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from which DSP values are allocated, and the authority responsible for
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allocating DSP values.
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.sh 2 "Supported Formats"
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.pp
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ARGO supports three types of ISO NSAP-addresses:
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one type with AFI 37(hex) and two types with AFI 47(hex).
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.sh 3 "AFI 37"
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.pp
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This value of the AFI defines the IDI to be an X.121 address or DTE
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address.
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The DTE address is encoded in binary coded decimal.
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The DSP syntax is binary.
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This form is intended to be used when communicating
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across a public data network (PDN).
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The ARGO software and documentation
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refer to this type of NSAP-address as a
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\*(lqtype 37.\*(rq
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address.
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.sh 3 "AFI 47"
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.pp
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The value of 47 for the AFI defines the IDI to be a 4 digit International
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Code Designator (ICD) allocated according to ISO 6523.
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ARGO support two
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ICD values.
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.sh 4 "ICD 0004"
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.pp
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The ICD value of 0004 is assigned to OSINET,
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an experimental OSI network overseen by
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National Institute of Science and Technology.\**
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.(f
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\** formerly the National Bureau of Standards
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.)f
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When this style of NSAP-address
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is used,
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the DSP is divided into four parts: an organization identifier (2 bytes),
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a subnet identifier (2 bytes),
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an SNPA-part (4-8 bytes), and
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an NSAP selector (1 byte).
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The use of these fields is defined by the OSINET steering committee.
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This type of address is known as an
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\*(lqOSINET\*(rq
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address.
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.sh 4 "ICD 0006"
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.pp
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The ICD value of 0006 is assigned to the Department of Defense (DoD).
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In ARGO, NSAP-addresses with an ICD value of 0006
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are of the format defined in RFC 986, a proposal for embedding DARPA Internet
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addresses within an OSI NSAP-address.
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In this case, the DSP takes the form:
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version (1 byte), DARPA Internet Address (4 bytes), upper layer protocol
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identifier (1 byte).
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This is called an
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\*(lqrfc986\*(rq
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address.
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.sh 1 "Internal Representation"
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.pp
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Internally, an NSAP address takes the form
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.(b
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\fC
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.TS
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tab(+);
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l s s s s.
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struct iso_addr {
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.T&
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l l l l l.
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+u_char+isoa_afi;+/* authority &
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+++format id */
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+union+{+
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++struct addr_37+addr_37;+/* x.121 */
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++struct addr_osinet+addr_osinet;+/* OSINET */
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++struct addr_rfc986+addr_rfc986;+/* Internet*/
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+}+isoa_u;
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+u_char+isoa_len;+/* length */
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}
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.TE
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\fR
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.)b
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The field \fIisoa_afi\fR contains the AFI for the address.
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The union
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\fIisoa_u\fR contains the remainder of the address.
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The length of the entire address (the AFI, IDI, and DSP) is
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stored in \fIisoa_len\fR.
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.sh 1 "Network Layer Routing"
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.pp
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Routing at the network layer is performed by the
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routing procedure \fIrtalloc()\fR as described in Chapter 5.
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\fIRtalloc()\fR was designed for used in the DoD Internet
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domain.
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An unfortunate
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effect of this is that routing decisions are based upon either the
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entire NSAP address or the network portion of the address.
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The problem is defining the network portion of an NSAP address.
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The location and extent of the
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network portion of an NSAP address depends on the
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style of NSAP address.
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This decision is made by the function \fIiso_netof()\fR.
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.sh 2 "Network Portion of Type 37 Addresses"
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.pp
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There is no network portion of an X.121 address.
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In ARGO, the network portion of a type 37 address
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is defined to be just the AFI.
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The obvious consequence of this is that all type 37 addresses will
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match all other type 37 addresses
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in a network-portion comparison.
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.sh 2 "Network Portion of OSINET Addresses"
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.pp
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The network portion of an OSINET address is the organization identifier and
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the subnet identifier.
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.sh 2 "Network Portion of RFC986 Addresses"
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.pp
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The network portion of an RFC986 address is the network portion of the
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embedded DARPA Internet address.
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ARGO does not support subnetting, a method of subdividing Internet addresses.
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.sh 1 "NSAP Address / Subnetwork Point of Attachment Mapping"
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.pp
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In order to transmit a packet on a real subnetwork, the destination
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NSAP address
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must be mapped to an SNPA address.
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An SNPA address is the real, "hardware" address
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of a system on a network.
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This address corresponds to the 6 byte Ethernet or Token Ring
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Adapter address,
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or to the DTE address, which may be up to 7 bytes
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long (14 decimal digits).
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.pp
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A table, \fIsnpa_cache\fR is kept in the kernel which contains the
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translation between NSAP-addresses and SNPA-addresses.
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This table is used by \fIiso_snparesolve()\fR whenever a
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datagram must be dispatched.
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The table is maintained by the the ISO ES-IS protocol entity.
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Entries can be added and deleted
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by the user program \fIclnlutil(8)\fR and
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by the CONS entity.
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