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Versions: 02

Interdomain Routing Working Group                   Yakov Rekhter
Internet Draft                                      cisco Systems
<draft-ietf-idr-idrp-v4v6-02.txt>                     Paul Traina
                                                    cisco Systems
                                                     January 1996



                         IDRP for IP v4 and v6


Status of this memo


   This document is an Internet Draft.  Internet Drafts are working
   documents of the Internet Engineering Task Force (IETF), its Areas,
   and its Working Groups.  Note that other groups may also distribute
   working documents as Internet Drafts.

   Internet Drafts are draft documents valid for a maximum of six
   months.  Internet Drafts may be updated, replaced, or obsoleted by
   other documents at any time.  It is not appropriate to use Internet
   Drafts as reference material or to cite them other than as a
   ``working draft'' or ``work in progress.''

   Please check the 1id-abstracts.txt listing contained in the
   internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net,
   nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the
   current status of any Internet Draft.


1 Overview


   IDRP [5] is defined as the protocol for exchange of Inter-Domain
   routing information between routers to support forwarding of ISO 8473
   (Connectionless Network Layer Protocol (CLNP))[6] packets.

   The network reachability information exchanged via IDRP provides
   sufficient information to detect routing loops and enforce routing
   decisions based on performance preference and policy constraints as
   outlined in RFC 1104 [1]. In particular, IDRP exchanges routing
   information containing full domain-level paths and enforces routing
   policies based on configuration information.

   IDRP may be viewed as an extension of BGP-4 ([9], [10]) that provides
   (among other things) much better scaling with respect to support for
   routing information aggregation based on CIDR ([2], [11]), as well as
   stronger capabilities for policy based routing (e.g. ability to
   impose control over transit traffic). Enhanced scaling capabilities
   are provided via the concept of Routing Domain Confederations (RDCs),
   that allow to express both topology and policy information in terms
   of aggregates (confederations) rather than individual entities
   (domains).  IDRP also provides capability to carry reachability and



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   forwarding information associated with multiple network layer
   protocols (e.g.  IPv6, IPv4).

   This  document  contains the  adaptation of the IDRP protocol
   definition that enables it to be used as a protocol for the exchange
   of inter-domain system routing information among routers to support
   the forwarding of IPv6 packets across multiple domains.  We refer to
   IDRP with this adaptation as "IDRP for IPv6".  While this document
   doesn't cover use of IDRP to support routing for other network layer
   protocols (e.g. IPv4), it is expected that IDRP for IPv6 will be able
   to operate in a multiprotocol environment as well.


2 Terminology


   This  document assumes that the reader is familiar with the following
   documents:

   IPv6 protocol specification [3], IPv6 Addressing Architecture [4],
   and IDRP specification (IS 10747) [5].

   A few definitions are in order to aid the reader:

      BIS - a Boundary Intermediate System (or border router)

      BISPDU - an IDRP message exchanged between a pair of BISs

      ES - End System (host)

      FIB - Forwarding Information Base (IP forwarding table)

      IS - Intermediate System (router)

      NET - Network Entity Title (a network layer address for a router)

      NLRI - Network Layer Reachability Information (set of reachable
      destinations)

      NPDU - an IPv6 packet

      NSAP - Network Service Access Point (a network layer address)

      PDU - a packet

      SNPA - subnetwork point of attachment (Data Link address)


   It is expected that the above definitions should be adequate for
   understanding of IDRP. Familiarity with any of the documents listed
   in the normative references of the protocol specifications (section 2
   of [5]) is not required.

   Unless stated otherwise here, any reference to the above terms in [5]



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   should be interpreted based on the above definitions.


3 The Adaptation Layer


   The Inter-Domain Routing Protocol (IDRP) or, more formally,

      "The Protocol for the Exchange of Inter-Domain Routing information
      among Intermediate Systems to support Forwarding of ISO 8473  PDUs
      (IDRP)"


   is the inter-domain routing protocol defined to support the
   forwarding of Connectionless Network Layer Protocol (CLNP) [6]
   packets that traverse multiple routing domains.

   IDRP document [5] covers both the protocol specifications and the
   usage issues (which is in contrast to BGP-4 documentation that has a
   separate document that defines the protocol [10], and a separate
   document that describes the protocol's usage [9]).

   While IDRP was developed within ISO, it makes few, if any, ISO-
   specific assumptions. In particular, it does not require
   participating domains to support any specific ISO Intra-Domain
   protocol, such as IS-IS [7], nor does it require participating
   routers to run ES-IS [8].

   The only requirements imposed by the protocol on the participating
   routers is that the protocol information can be exchanged among them
   over a connectionless network layer (which in the case of OSI is
   CLNP), and that the network layer connectivity  between routers
   within a single routing domain should be provided by means outside of
   IDRP (e.g., via some  intra-domain routing  protocol). IDRP does not
   place any restrictions on the structure of reachability information,
   as long it can be expressed as an arbitrary set of variable length
   address prefixes.

   Since IPv4 and IPv6 can provide connectionless service between
   routers, and since reachable IPv4/IPv6 destinations can be expressed
   as IP address prefixes, IDRP can be  easily adapted to be an inter-
   domain routing protocol which can be used in the IP Internet.

   The adaptation described in this document consists of: specifying the
   parts of the protocol that are not needed, specifying
   modifications/clarifications to certain parts of the protocol to
   reflect IP specifics and operational experience with BGP-4, adding
   new features to reflect operational experience with BGP-4.


4 Features in IDRP which shall not be implemented


   The following lists the functions that shall not be implemented by



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   IDRP for IPv4 an IPv6 (all references are with respect to [5]):

   Support for distinguishing path attributes according to sections 5.7,
   7.11.2 and 7.11.3 Expense according to section 7.12.10 Security
   according to section 7.12.14 Priority according to section 7.12.16
   Procedures for detecting inconsistent routing decisions, according to
   section 7.15.1 Forwarding CLNP packets according to section 8 The
   interface to CLNP according to section 9 support of the Network
   Management information described in the IDRP GDMO according to
   section 11

   All the material presented in the sections listed above may be
   ignored.


5 Features in IDRP which shall be implemented


   An implementation of IDRP for IPv4 and IPv6 shall contain all
   mandatory features
    of IDRP, except those  mentioned in section 4 of this document. In
   addition, a BIS for IDRP for IPv4 and IPv6 shall implement the
   following (all references are with respect to this document):

   an interface to the IPv4 and IPv6 protocol, as described in section
   5.1 Modifications to the encoding of reachability and forwarding
   information, as well as the ability to identify and extract IPv4 and
   IPv6 reachability and forwarding information as described in sections
   5.2 and 5.3 Modifications to the ROUTE_SEPARATOR and
   MULTI_EXIT_DISCRIMINATOR path attributes, as described in section 5.4
   Support for the ATOMIC_AGGREGATE path attribute, as described in
   section 5.5 Modifications to the tie-breaking procedures, as
   described in sections 5.6 Modifications to handling Hold Time, as
   described in section 5.7 Constructing forwarding address (next hop),
   as described in section 5.8 Modifications to the UPDATE PDU format,
   as described in section 5.9 Modifications to the OPEN PDU format, as
   described in section 5.10 Modifications to the RIB REFRESH PDU
   format, as described in section 5.11 New Error Subcodes, as described
   in section 5.12

   Naming and addressing conventions discussed in sections 5.10, 5.11
   and 7.1 of [5] do not apply to IDRP for IPv4 and IPv6, and thus
   should be ignored.  Section 6 of this document contains the material
   that covers naming and addressing conventions for IDRP for IPv4 and
   IPv6.

   Deployment guidelines for IDRP for IPv4 and IPv6 are specified in
   section 7 of this document. These guidelines supersede the material
   presented in section 7.2 of [5].

   Domain configuration information for IDRP for IPv4 and IPv6 is
   defined in section 8 of this document. The material of that section
   supersedes the material presented in section 7.3 of [5].




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5.1 An interface to IP


   This sections supersedes the material in section 7.5 of [5].

   IDRP information is carried between a pair of BISs in the form of
   BISPDUs. For IDRP for IPv6 these BISPDUs are carried in the data
   field of IP packets of protocol type 45.

   IDRP relies on IP to perform the initial processing of incoming
   BISPDUs. The IP protocol machine shall process inbound packets
   according to the appropriate IP functions.

   If a fixed header of an IP packet contains a protocol type that
   identifies IDRP, and the packet's source address identifies any
   system listed in managed objects internalBIS or externalBISNeighbor,
   then the packet contains a BISPDU. The BISPDU shall be passed to the
   IDRP finite state machine defined in section 7.6.1 of [5].


5.2 Encoding IP reachability information


   The text in this section supersedes the material presented in section
   6.3.2 of [5].

   The Network Layer Reachability information is a variable length field
   that contains a list of reachable destinations encoded as zero or
   more triples of the form <Address Family, Addr_length, Addr_info>,
   whose fields are described below:

      +---------------------------+
      | Address Family (2 octets) |
      +---------------------------+
      | Addr_length (2 octets)    |
      +---------------------------+
      | Addr_info (variable)      |
      +---------------------------+

   The use and meaning of these fields are as follows:

      Address Family:
         This field carries the identity of the protocol associated with
         the address information that follows. Presently defined values
         for this field are specified in RFC1700.  A conformant
         implementation of IDRP for IPv6 may ignore any address
         information indicating other than IPv6.  A conformant
         implenetation of IDRP for IPv4 may ignore any address
         information indicating other than IPv4.  Address Family.

      Addr_Length:
         This field specifies the total length in octets of the address
         information that follows.




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      Addr_Info:
         This is a variable length field that contains a list of IP
         address prefixes for the routes that are being advertised.
         Each IP address prefix is encoded as a 2-tuple of the form
         <Length, Prefix>, whose fields are described below:

            +---------------------------+
            |   Length (1 octet)        |
            +---------------------------+
            |   Prefix (variable)       |
            +---------------------------+


         The use and the meaning of these fields are as follows:

         a) Length:

            The Length field indicates the length in bits of the IP
            address prefix. A length of zero indicates a prefix that
            matches all IPv4 or IPv6 (as specified by the address
            family) addresses (with prefix, itself, of zero octets).

         b) Prefix:

            The Prefix field contains IP address prefixes followed by
            enough trailing bits to make the end of the field fall on an
            octet boundary.  Note that the value of trailing bits is
            irrelevant.


5.3 Encoding IP forwarding information


   IPv6 forwarding information is carried in the NEXT_HOP path
   attribute.  As specified in [5], the attribute has a Proto_type,
   Proto_Length and Protocol fields which indicate the protocol family
   for the address of the NEXT_HOP (see section 6.3.1.4 of [5]).  This
   document replaces these three fields (Proto_type, Proto_Length, and
   Protocol) with a single field -- Address Family.  This 2-octets field
   carries the identity of the protocol associated with the address
   information that follows. Presently defined values for this field are
   specified in RFC1700.  A conformant implementation of IDRP for IPv6
   may ignore any address information indicating other than IPv6 Address
   Family.  A conformant implementation of IDRP for IPv4 may ignore any
   address information other than the IPv4 Address Family.

   An implementation of IDRP for IPv4 or IPv6 shall have the following
   values in the NEXT_HOP field:

   IPv6:
      Length of NET: 16

      NET of Next Hop: an IPv6 unicast address




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      SNPA information:  as appropriate for the subnetwork type in use

   IPv4:
      Length of NET: 4

      NET of Next Hop: an IPv4 unicast address

      SNPA information:  as appropriate for the subnetwork type in use


   All other fields of the NEXT_HOP attribute remains as specified in
   [5].


5.4  Modification to the existing path attributes


   To facilitate operations, IDRP for IPv6 modifies the following path
   attributes:

   LOCAL_PREF field in the ROUTE_SEPARATOR attribute (see section
   6.3.1.1) is changed from 1 octet to 4 octets. The ROUTE-ID field in
   the ROUTE_SEPARATOR attribute is eliminated. As a result the length
   of the ROUTE_SEPARATOR attribute is changed from 5 to 4 octets.  The
   length of the MULTI_EXIT_DISCRIMINATOR attribute is changed from 1
   octet to 4 octets.

   Semantics, as well as handling of the modified attributes is left
   intact.


5.5  New path attributes


   IDRP for IPv6 defines the following new attribute:

         AGGREGATOR (Type Code 17):

            AGGREGATOR is an optional transitive attribute of length 32.
            The attribute contains the last RDI that formed the
            aggregate route (encoded as 16 octets), followed by the IP
            address of the BIS that formed the aggregate route (encoded
            as 16 octets, IPv4 addresses are prefixed with 12 octets of
            zeros). The BIS that formed the aggregate route may decline
            to encode its address and instead insert a value of all
            zeros into that field.

            The attribute may be included in routes which are formed by
            route aggregation. A BIS that performs the aggregation may
            add the AGGREGATOR attribute which shall contain BIS's own
            RDI and IPv6 address.

         ATOMIC_AGGREGATE (Type Code 18):




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            ATOMIC_AGGREGATE is a well-known discretionary attribute of
            length 0.  It is used by a BIS to inform other BISs that the
            local system selected for advertisement a less specific
            route without selecting a more specific route which is
            included in it.

            If a BIS, when presented with a set of overlapping routes
            from one of its peers, selects the less specific route
            without selecting the more specific one, then the local
            system shall attach the ATOMIC_AGGREGATE attribute to the
            route when propagating it to other BISs (if that attribute
            is not already present in the received less specific route).
            A BIS that receives a route with the ATOMIC_AGGREGATE
            attribute shall not remove the attribute from the route when
            propagating it to other BISs. A BIS that receives a route
            with the ATOMIC_AGGREGATE attribute shall not make any NLRI
            of that route more specific when advertising this route to
            other BISs.  A BIS that receives a route with the
            ATOMIC_AGGREGATE attribute needs to be cognizant of the fact
            that the actual path to destinations, as specified in the
            NLRI of the route, while having the loop-free property, may
            traverse domains/confederations that are not listed in the
            RD_PATH attribute.


5.6  Modifications to tie-breaking procedures for phase 2


   This section supersedes the material in section 7.16.2.1 and 7.16.1.1
   of [5].

   In its Adj-RIBs-In a BIS may have several routes to the same
   destination that have the same degree of preference. The local BIS
   can select only one of these routes for inclusion in the associated
   Loc-RIB. The local BIS considers all equally preferable routes, both
   those received from BISs located in adjacent RDs, and those received
   from other BISs located in the local BIS's own RD.

   Ties shall be broken according to the following algorithm:

      a) If the local BIS is configured to take into account
      MULTI_EXIT_DISC, and the candidate routes differ in their
      MULTI_EXIT_DISC attribute, select the route that has the lowest
      value of the MULTI_EXIT_DISC attribute.  If the local BIS is
      configured to take into account MULTI_EXIT_DISC,  but that
      attribute is not present,  a locally defined "default"
      MULTI_EXIT_DISC may be assumed as a basis for performing tie-
      breaking.

      b) Otherwise, if the local BIS can ascertain the cost of a path to
      the entity depicted by the NEXT_HOP attribute of the candidate
      route, select the route with the lowest cost (interior distance)
      to the entity depicted by the NEXT_HOP attribute of the route.  If
      there are several routes with the same cost, then the tie-breaking



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      shall be broken as follows:

         - if at least one of the candidate routes was advertised by the
         BIS in an adjacent RD, select the route that was advertised by
         the BIS in an adjacent RD whose address has the lowest value
         among all other BIS in adjacent RDs;

         - otherwise, select the route that was advertised by the BIS
         whose address has the lowest value.


5.7  Modifications to handling Hold Time


   Upon receipt of an OPEN BISPDU, a BIS must calculate the value of the
   Hold Timer by using the smaller of its configured Hold Time and the
   Hold Time received in the OPEN BISPDU.

   IDRP for IPv6 requires the value of the Hold Time field carried in
   the OPEN BISPDU to be either zero or at least 3 seconds.  An
   implementation must reject Hold Time values of one or two seconds.
   An implementation may reject any proposed Hold Time. An
   implementation which accepts a Hold Time must use the negotiated
   value for the Hold Time.  If the negotiated Hold Time interval is
   zero, then periodic KEEPALIVE messages shall not be sent.

   In addition to the OPEN PDU error handling procedures specified in
   section 7.20.2 of [5] this document specifies that if the Hold Time
   field of the OPEN message is unacceptable, then the Error Subcode
   shall be set to Unacceptable Hold Time.


5.8 Determining the forwarding address (Next Hop)


   Next hop forwarding information information associated with a
   particular route shall be derived from the NEXT_HOP attribute in the
   UPDATE BISPDU that carries the route. If that attribute is not
   present, the next hop (forwarding address) shall be derived from the
   source IPv6 address of the IPv6 packet that carries the UPDATE BISPDU
   containing the route.

   In addition to the procedures for handling the NEXT_HOP attribute
   specified in section 7.12.4 of [5], IDRP for IPv4 and IPv6 specifies
   the following:

   A BIS must never advertise an address of a peer to that peer as a
   NEXT_HOP, for a route that the speaker is originating.  A BIS must
   never install a route with itself as the next hop.  When a BIS
   advertises the route to a BIS located in its own domain, the
   advertising BIS should not modify the NEXT_HOP attribute associated
   with the route.  When a BIS receives the route from an internal
   neighbor BIS, it may use the NEXT_HOP address as the forwarding
   address, provided that the address is on a common subnet with the



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   local BIS.


5.9 Modifications to the UPDATE PDU


   This document specifies that NLRI of a route, rather than the Route-
   ID of the route, shall be used to withdraw a previously advertised
   route from service.

   The Withdrawn Routes field in the UPDATE PDU is specified as a
   variable length field that contains a list of NLRIs (rather than the
   list of Route-IDs) for the routes that are being withdrawn from
   service. Each NLRI is encoded as specified in Section 5.2 of this
   document.  An UPDATE PDU can list multiple routes to be withdrawn
   from service.  Each such route is identified by its NLRI, which
   unambiguously identifies the route in the context of the BIS-BIS
   connection in which it had been previously been advertised.

   Eliminating Route-ID is also reflected in the encoding of the
   ROUTE_SEPARATOR attribute (see Section 5.4 of this document).


5.10 Modifications to the OPEN PDU


   Since IDRP for IPv6 doesn't support any Distinguishing Attrbutes, the
   RIB-AttsSet field is eliminated from the OPEN PDU. (PST--bring back
   DA's?)

   The last two fields of the OPEN PDU message, Authentication Code and
   Authentication Data, are replaced with the following two fields:

      Optional Parameters Length:

         This 2-octet unsigned integer indicates the total length of the
         Optional Parameters following this field in octets. If the
         value of this field i s zero, no Optional Parameters are
         present.

      Optional Parameters:

         This field may contain a list of optional parameters, where
         each parameter is encoded as a <Parameter Flags, Parameter
         Type, Parameter Length, Parameter Value> vector.

             0                   1                   2
             0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
            |  Parm Flags   |  Parm. Type   | Parm. Length  |  Parameter Value (variable)
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...


            (PST: grab BGP/4 flags text and talk to yakov about making



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            length extensible
             just like attribute length in BGP)

         Parameter Flags is a one octet field that (PST: grab text from
         BGP-4)

         Parameter Type is a one octet field that unambiguously
         identifies individual parameters. Parameter Length is a one
         octet field that contains the length of the Parameter Value
         field in octets.  Parameter Value is a variable length field
         that is interpreted according to the value of the Parameter
         Type field.

         This document defines the following Optional Parameters:

         a) Authentication Information (Parameter Type 1):


            This optional parameter may be used to authenticate a BIS
            peer. The Parameter Value field contains a 1-octet
            Authentication Code followed by a variable length
            Authentication Data.

                0 1 2 3 4 5 6 7 8
               +-+-+-+-+-+-+-+-+
               |  Auth. Code   |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               |      Authentication Data (variable)                 |
               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            The syntax and semantics of these two field is left
            unchanged (as specified in section 6.2 of [5]).

   Absence of any Authentication Information in an OPEN PDU shall be
   treated as if the PDU carries Authentication Information with
   Authentication Type 1 (see section 7.1.1 of [5]).

   In addition to the OPEN PDU error handling procedures specified in
   section 7.20.2 of [5] this document specifies that if one of the
   Optional Parameters in the OPEN message is not recognized, then the
   Error Subcode is set to Unsupported Optional Parameters.


5.11 Modifications to the RIB REFRESH PDU


   This sections supersedes the material in section 6.7 of [5].

   The RIB REFRESH PDU is used to allow a BIS to send a refresh of the
   routeing information in an Adj-RIB-Out to a neighbor BIS, or to
   solicit a neighbor BIS to send a refresh of its Adj-RIB-Out to the
   local BIS.  The RIB REFRESH PDU contains a fixed header and also the
   additional fields shown below:




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      +---------------------------------------+
      | Fixed Header                          |
      +---------------------------------------+
      | OpCode (1 octet)                      |
      +---------------------------------------+
      | Optional Parameter Length (1 octet)   |
      +---------------------------------------+
      | Optional Parameters (variable)        |
      +---------------------------------------+

   The use and meaning of these fields is as follows:

      There are three OpCode values defined:

         +------------+---------------------+
         | Code       | Operation           |
         +------------+---------------------+
         | 1          | RIB Refresh Request |
         +------------+---------------------+
         | 2          | RIB Refresh Start   |
         +------------+---------------------+
         | 3          | RIB Refresh End     |
         +------------+---------------------+


      Optional Parameters Length:
         This 1-octet unsigned integer indicates the total length of the
         Optional Parameters field in octets. If the value of this field
         is zero, no Optional Parameters are present.

      Optional Parameters:
         This field may contain a list of optional parameters, where
         each parameter is encoded as a <Parameter Type, Parameter
         Length, Parameter Value> triplet.

             0                   1
             0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...
            |  Parm. Type   | Parm. Length  |  Parameter Value (variable)
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...


         Parameter Type is a one octet field that unambiguously
         identifies individual parameters. Parameter Length is a one
         octet field that contains the length of the Parameter Value
         field in octets.  Parameter Value is a variable length field
         that is interpreted according to the value of the Parameter
         Type field.

   When a BIS receives a RIB REFRESH PDU that contains one or more
   Optional Parameters, and the BIS doesn't support or does't recognize
   at least one of the parameters, the BIS processes the PDU as if it
   wouldn't have any Optional Parameters. This document doesn't specify
   any Optional Parameters.



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   Usage of RIB REFRESH PDU is defined in 7.10.3 of [5].


5.12 Additional Error Subcodes


   In addition to the Error subcodes defined in section 5.4 of [5], this
   document defines the following OPEN PDU Error subcodes:


      8 - Unacceptable Hold Time (see Section 5.7 of this document)

      9 - Unsupported Optional Parameter (see Section 5.12 of this
      document)



6 Naming and addressing conventions


   This section supersedes the material of sections 5.10, 5.11 and 7.1
   of [5].

   IDRP for IPv4 and IPv6 does not assume or require any particular
   structure for IP addresses. That is, as long as the domain
   administrator assigns addresses that are consistent with the
   deployment constraints of section 7 of this document, the protocol
   will operate correctly.

   IP address prefixes provide a compact way for identifying groups of
   systems that reside in a given domain or confederation. A prefix may
   have a length that is either smaller than, or the same size as the IP
   address (an IPv4 or IPv6 address is a special case of an address
   prefix). The length of an encoded prefix is specified in bits.

   Each routing domain and routing domain confederation whose BIS(s)
   implement IDRP for IPv4 and IPv6 shall have an unambiguous routing
   domain identifier (RDI), which is an IPv4 or IPv6 address prefix.  In
   the case of IPv4 address prefixes, the prefix value shall be
   prepended with 12 octets of zeros.

   An RDI is assigned statically and does not change based on the
   operational status of a routing domain. An RDI identifies routing
   domain or confederation uniquely, but does not necessarily convey any
   information about policies or identities of its members.


7  Deployment guidelines


   This section supersedes the material in section 7.2 of [5].

   Hosts and routers may use any IP unicast addresses, provided that
   these addresses are globally unambiguous. However correct and



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   efficient operation of this protocol can only be guaranteed if the
   address assignment reflects the actual topology -- addresses are
   topologically significant. One possible architecture for IPv6 address
   assignment that satisfies this requirement is described in [12].


8  Domain Configuration Information


   Correct Operation  of  IDRP described  in [5] assumes that a minimum
   amount of information  is  available to both the inter-domain  and
   intra-domain routing protocols. This information  is static in
   nature, and is not expected to change frequently.  This document
   assumes that this information is supplied via IDRP MIB. While the
   following in phrased in terms of MIB, this document allows
   alternative mechanisms (e.g. configuration files) as well.

   The information required  by a BIS that implements the IDRP for IPv4
   and IPv6 protocol is:

   Location and identity of adjacent Intra-Domain routers:

   The MIB table IntraIS lists the IP addresses of the routers to which
   the local BIS may deliver an inbound NPDU whose destination lies
   within the BIS's routing domain. These routers listed in the IntraIS
   table support the intra-domain routing protocol of this domain, and
   share at least one common subnet with the BIS.

   In particular, if the local BIS participates in both  the inter-
   domain routing protocol (IDRP) and the intra-domain  routing
   protocol, then the IP address of the local BIS will be listed in the
   IntraIS table.

   Location and identity of BISs in the BIS's domain:

   This information permits a BIS to identify all other BISs located
   within its routing domain. This information is contained in the MIB
   table InternalBIS, which contains a set of IPv6 addresses which
   identify the BISs in the domain.

   Location and identity of BISs in adjacent domains:

   Each BIS needs information to identify the IP address of each BIS
   located in an adjacent RD and reachable via a single subnetwork hop.
   This information is contained in the IDRP MIB table
   externalBISNeighbor, which is a table of IPv6 addresses.

   IP network address information for all systems in the routing domain:

   This information is used by the BIS to construct its network layer
   reachability information. This information is contained in the MIB
   table internalSystems, which lists NLRI (expressed as address
   prefixes) of the systems within the routing domain.




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   Local RDI:

   This information is contained in managed object localRDI; it is the
   RDI of the routing domain in which the  BIS is located.

   RDC-Config:

   This information identifies all the routing domain confederations
   (RDCs) to which the RD of the local BIS belongs, and it describes the
   nesting relationships that are in force between them. It is contained
   in the MIB table rdcConfig.

   Note that since a domain is not required to belong to a confederation
   this information is optional and needs to be present only at BISs of
   the domains that are part of one or more of RDCs.



9 Multiple IDRP sessions between the same pair of routers


   An IP router may have multiple IP addresses,  one for each interface.
   In contrast, an OSI Intermediate System has only one Network Entity
   Title (network address). An OSI BIS thus may not have multiple IDRP
   sessions with another BIS, since the NET is unique and there is no
   mechanism for multiplexing sessions. However, an IP router may
   potentially have multiple IDRP sessions with another router, since
   each BIS may have multiple IP addresses, and one BIS may not be able
   to ascertain that those addresses correspond to the same BIS.
   Multiple IDRP sessions between BISs may not be efficient, but they
   are not illegal, nor do they impact the robustness of the IDRP for IP
   protocol; they will simply appear as multiple paths to the same
   neighboring domain. One possible way of avoiding multiple parallel
   IDRP sessions between a pair of BISs within a single domain is to
   bind all source addresses of outgoing BISPDUs to  the IPv6 address of
   a particular interface (either physical or logical) of the BIS.
   Likewise, for a pair of BISs located in adjacent domains, binding the
   source addresses to a single address of an interface attached to a
   common subnetwork allows for the elimination of multiple parallel
   sessions.

10 Required set of supported routing policies


   Policies are provided to IDRP in the form of configuration
   information.  This information is not directly encoded in the
   protocol.  Therefore, IDRP can provide support for very complex
   routing policies (an example of such policy is presented in Annex K
   of [5]).  However, it is not required that all IDRP implementations
   support such policies.

   We are not attempting to standardize the routing policies that must
   be supported in every IDRP implementation; we strongly encourage all
   implementors to support the following set of routing policies:



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   IDRP implementations should allow a domain to control announcements
   of IDRP-learned routes to adjacent domains.  Implementations should
   also support such control with at least the granularity of a single
   address prefix.  Implementations should also support such control
   with the granularity of a domain, where the domain may be either the
   domain that originated the route, or the domain that advertised the
   route to the local system (adjacent domain).  Care must be taken when
   a BIS selects a new route that can't be announced to a particular
   external peer, while the previously selected route was announced to
   that peer.  Specifically, the local system must explicitly indicate
   to the peer that the previous route is now infeasible.  IDRP
   implementations should allow a domain to prefer a particular path to
   a destination (when more than one path is available).  At the minimum
   an implementation shall support this functionality by allowing to
   administratively assign a degree of preference to a route based
   solely on the IP address of the neighbor the route is received from.
   The allowed range of the assigned degree of preference shall be
   between 0 and 2^(31) - 1.  IDRP implementations should allow a domain
   to ignore routes with certain domains in the RD_PATH path attribute.
   Such function can be implemented by assigning "infinity" as "weights"
   for such domains. The route selection process must ignore routes that
   have "weight" equal to "infinity".


11 Operations over Switched Virtual Circuits


   When using IDRP for IPv4 and IPv6 over Switched Virtual Circuit (SVC)
   subnetworks it may be desirable to minimize traffic generated by
   IDRP.  Specifically, it may be desirable to eliminate traffic
   associated with periodic KEEPALIVE messages.  IDRP for IPv4 and IPv6
   includes a mechanism for operation over switched virtual circuit
   (SVC) services which avoids keeping SVCs permanently open and allows
   it to eliminates periodic sending of KEEPALIVE messages.

   This section describes how to operate without periodic KEEPALIVE
   messages to minimize SVC usage when using an intelligent SVC circuit
   manager.  The proposed scheme may also be used on "permanent"
   circuits, which support a feature like link quality monitoring or
   echo request to determine the status of link connectivity.

   The mechanism described in this section is suitable only between the
   BISs that are directly connected over a common virtual circuit.

11.1 Establishing an IDRP Connection


   The feature is selected by specifying zero Hold Time in the OPEN
   BISPDU.

11.2 Circuit Manager Properties


   The circuit manager must have sufficient functionality to be able to



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   compensate for the lack of periodic KEEPALIVE BISPDU:

   It must be able to determine link layer unreachability in a
   predictable finite period of a failure occurring.  On determining
   unreachability it should: start a configurable dead timer (comparable
   to a typical Hold timer value).  attempt to re-establish the Link
   Layer connection.

   If the dead timer expires it should: send a deactivate indication to
   IDRP FSM.  If the connection is re-established it should: cancel the
   dead timer.  transmit any queued BISPDUs.

11.3 Combined Properties


   Some implementations may not be able to guarantee that the IDRP
   process and the circuit manager will operate as a single entity; i.e.
   they can have a separate existence when the other has been stopped or
   has crashed.

   If this is the case, a periodic two-way poll between the IDRP process
   and the circuit manager should be implemented.  If the IDRP process
   discovers the circuit manager has gone away it should close all
   relevant BIS-BIS connections.  If the circuit manager discovers the
   IDRP process has gone away it should close all its BIS-BIS
   connections associated with the IDRP process and reject any further
   incoming BIS-BIS connections.



12 Modifications to the conformance clause


   To reflect the list of functions that shall not be implemented (see
   section 4 of this document) the following items in the  IDRP
   conformance clause (section 12.1 of [5]) shall not be implemented:

   clause (d):  Transit Delay, Residual Error, Expense, clause (m)
   clause (r) clause (s) clause (t)


13 Modifications to PICS


   The PICS (Protocol Implementation Conformance Statement) provides a
   convenient and  concise mechanism  to define which function need and
   need not be implemented  for IDRP for IPv4 and IPv6.  All references
   in this section  are with respect to [5].

   All items with PICS  Status as Optional need not be implemented in
   IDRP for IPv4 and IPv6. In addition, IDRP for IPv4 and IPv6 should
   not support the following items (even if some of the items are listed
   as Mandatory):




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      Table A.4.3:
         MGT

      Table A.4.5:
         INCONS

      Table A.4.8:
         PSRCRT, DATTS, MATCH

      Table A.4.11:
         TDLY, RERR, EXP, LQOSG, SECG, PRTY

      Table A.4.12:
         TDLYP, RERRP, EXPP, LQOSP, SECP, PRTYP

      Table A.4.13:
         TDLYR, RERRR, EXPR, LQOSR, SECR, PRTYR


   Implementation of all other items with Optional Status not listed in
   the previous paragraph is optional.


14 Navigating through IDRP


   Here is the list of sections in [5] that are relevant to  the IDRP
   for IPv6 implementation: chapters 1, 3, 4, 5 (except 5.10 and 5.11),
   6, 7 (except for 7.1, 7.2, 7.3, 7.4, 7.12.8, 7.12.9, 7.12.10, 7.12.11
   and 7.12.16), 10.  The rest of the material in [5] could be safely
   ignored.


15 Security Considerations


   Security issues are not discussed in this document.


16 Acknowledgements


   Large parts of this document are borrowed from the BGP Protocol
   specifications and BGP Usage documents ([9], [10]).

   We would like to thank Susan Hares (MERIT) and John Scudder (MERIT)
   for their work on IDRP for IPv4. Portions of this document are
   borrowed from their work.

   We would like to thank Tony Li (cisco Systems) for his review of this
   document.

   Finally we would like to thank the whole Inter-Domain Routing (IDR)
   Working Group for their contribution to this document.



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17 References


   [1] Braun, H-W., "Models of Policy Based Routing", RFC 1104,
   Merit/NSFNET, June 1989.

   [2] Fuller, V., Li, T., Yu, J., Varadhan, K., "Classless Inter-Domain
   Routing (CIDR): an Address Assignment and Aggregation Strategy", RFC
   1519, September 1993

   [3] Deering, S., Hinden, B., "Internet Protocol, Version 6 (IPv6)
   Specification", RFC1883, January 1996

   [4] Hinden, B., Deering, S., "IP Version 6 Addressing Architecture",
   RFC1884, January 1996

   [5] ISO/IEC IS 10747 - Information Processing Systems -
   Telecommunications and Information Exchange between Systems -
   Protocol for Exchange of Inter-domain Routing Information among
   Intermediate Systems to Support Forwarding of ISO 8473 PDUs, 1993
   ftp://networking.raleigh.ibm.com/pub/standards/idrp/is10747.ps
   ftp://networking.raleigh.ibm.com/pub/standards/idrp/is10747.txt

   [6] ISO 8473 - Information  Processing Systems - Data Communications
   - Protocol for Providing the Connectionless-mode Network Service,
   1988.

   [7] ISO/IEC 10589 - Information Processing Systems -
   Telecommunications and Information Exchange between systems -
   Intermediate System to Intermediate System Intra-Domain routing
   information exchange protocol for use in conjunction with the
   Protocol for providing the Connectionless-mode Network Service (ISO
   8473), 1992.

   [8] ISO 9542 - Information Processing Systems - Telecommunications
   and information exchange between systems - End system to Intermediate
   system routing exchange protocol for use in conjunction with the
   Protocol for providing the connectionless-mode network service (ISO
   8473)

   [9] Rekhter, Y., Gross, P., ``Application of the Border Gateway
   Protocol in the Internet'', RFC1655, July 1994

   [10] Rekhter, Y., Li, T., ``A Border Gateway Protocol 4 (BGP-4)'',
   RFC1654, July 1994

   [11] Rekhter, Y., Li, T., "An Architecture for IP Address Allocation
   with CIDR", RFC1518, September 1993

   [12]  Rekhter, Y.,  Li, T., "An Architecture for IPv6 Unicast Address
   Allocation", RFC1887, January 1996






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Authors' Addresses



   Yakov Rekhter
   cisco Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA 95134
   email: yakov@cisco.com

   Paul Traina
   cisco Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA 95134
   email: pst@cisco.com










































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