Network Working Group Susan Hares Request for Comments: DRAFT NSFNET/MERIT draft-ietf-ipidrp-sip-01.txt October 1993 IDRP for SIP Status of this memo This memo specifies the adaptation of the ISO Inter-Domain Routing Protocol ([1]) that enables it to be used as an inter-domain routing protocol in the Internet that supports SIP/IPAE ([6], [8]). IDRP with this adaptation will be called "IDRP for SIP" in this document. Multiprotocol IDRP, that is, a single instance of IDRP that can simultaneously support Inter-Domain/Inter-Autonomous System routing for multiple network layer protocols (e.g. SIP, IP, CLNP) Internets is outside the scope of this document. 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." 1. Overview IDRP ([1]) 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))[3] PDUs. 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 [7]. 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 [12] that provides (among other things) much better scaling with respect to support for routing Expiration Date April 1994 [Page 1] draft-ietf-ipidrp-sip-01.txt October 1993 - 2 - information aggregation and reduction based on CIDR, as well as stronger capabilities for policy based routeing (e.g. ability to impose control over transit traffic). IDRP also provides capability to carry reachability and forwarding information associated with multiple network layer protocols (e.g. SIP, IP, CLNP). This document contains the appropriate 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 SIP packets across multiple domains. The adaptation is defined is such a way that a Multiprotocol IDRP will be able to fully interoperate with IDRP for SIP. 2. Terminology This document assumes that the reader is familiar with the following documents: - SIP protocol specification [6], and - IDRP specification (IS 10747). 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 FIB - Forwarding Information Base (IP forwarding table) IS - Intermediate System (router) NET - Network Entity Title - an ISO network address for a router NLRI - Network Layer Reachability Information (set of reachable destinations) NPDU - an SIP packet PDU - a packet SNPA - subnetwork point of attachment (MAC address) Expiration Date April 1994 [Page 2] - 3 - draft-ietf-ipidrp-sip-01.txt October 1993 3. Assumptions The IDRP for SIP protocol assumes that within a single connected internet network addresses are unique. The uniqueness of SIP addresses is assumed to be provided by means outside of the protocol. The IDRP for SIP protocol cannot be guaranteed to work in an environment where network addresses within a single connected internet are not unique. All of the discussions in this document are based on the assumption that the Internet is a collection of arbitrarily connected domains. That is, the Internet will be modeled as a general graph whose nodes are domains and whose edges are connections between pairs of domains. The classic definition of a domain is a set of routers under a single technical administration, using an interior gateway protocol and common metrics to route packets within the domain and using an exterior gateway protocol to route packets to other domains. Since this classic definition was developed, it has become common for a single domain to use several interior gateway protocols and sometimes several sets of metrics within a domain. The use of the term domain here stresses the fact that, even when multiple IGPs and metrics are used, the administration of a domain appears to other domains to have a single coherent interior routing plan and presents a consistent picture of which networks are reachable through it. Domains are assumed to be administered by a single administrative entity, at least for the purposes of representation of routing information to systems outside of the domain. 4. The Adaptation Layer The Inter-Domain Routing Protocol (IDRP) or, more formally, "The Protocol for the Exchange of Inter-Domain Routeing 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) [ISO 8473] packets that traverse multiple routing domains. While this protocol was developed within ISO, it make 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 (ISO IS 10589)[4], nor does it require participating routers to run ES-IS (ISO 9542) [5]. The only Expiration Date April 1994 [Page 3] - 4 - draft-ietf-ipidrp-sip-01.txt October 1993 requirements imposed by the protocol on the participating routers is that the protocol information can be exchanged between 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 SIP can provide connectionless service between routers, and since reachable SIP destinations can be expressed as SIP address prefixes, IDRP can be easily adapted to be an inter-domain routing protocol which can be used in the pure SIP Internet. Certain IDRP Distinguishing Attributes may be used in conjuction with the Flow Label field in the SIP header. At the present moment the content of that field is specified to be an extension of the IP Type of Service (Tos) field. Mapping between the following IDRP Distinguishing Attributes - Transit Delay - Residual Error - Expense and the SIP Type of Service (TOS) parameters is defined in Section 5.2.3 of this document. While conceptually it should be possible to define mapping between other IDRP Distinguishing Attributes and the Flow Label, such definition is outside the scope of this document. Therefore, the use of the following IDRP Distinguishing Attributes for SIP packets will not be defined in this document: - Priority - Locally Defined QOS - Security Note that an implementation that does not support any of the NPDU-derived Distinguishing Attributes can fully interoperate with an implementation that does support them. Therefore, an IDRP for SIP implementation that will support routing sensitive to the parameters present in the TOS field of the SIP header will be compatible with the implementation that does not provide such support. Expiration Date April 1994 [Page 4] - 5 - draft-ietf-ipidrp-sip-01.txt October 1993 5. Implementor's Guide for SIP specific functions. In order to implement IDRP for SIP, only a subset of the features of the IDRP protocol must be implemented. 5.1 Features in IDRP which shall not be implemented The functions of the IDRP protocol which shall not be implemented for IDRP for SIP are those functions which deal with the following (all references are with respect to the IDRP document [1]): - Locally Defined QOS according to section 7.12.11 - Security according to section 7.12.14 - Priority according to section 7.12.16 - 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 Therefore, with IDRP for SIP the following items dealing with CLNP in the IDRP conformance clause (section 12.1 of [1]) shall not be implemented: - clause (d): Locally Defined QOS, Security, Priority - clause (r) - clause (s) - clause (t) 5.1.1 PICS Table Information 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 SIP. All references in this section are with respect to [1]. All items with PICS Status as Optional need not be implemented in IDRP for SIP. Specifically, IDRP for SIP does not require (and, indeed, does not need) support for Expiration Date April 1994 [Page 5] - 6 - draft-ietf-ipidrp-sip-01.txt October 1993 the following items: A.4.3 Table 9: MGT A.4.8 (Table 14): PSRCRT, DATTS A.4.11 (Table 17): LQOSG, SECG, PRTY A.4.11 (Table 18): LQOSP, SECP, PRTYP A.4.11 (Table 19): LQOSR, SECR, PRTYR Implementation of all other items with Optional Status not listed in the previous paragraph is optional. 5.2 Features in IDRP which shall be implemented An implementation of IDRP for SIP shall contain all mandatory features of IDRP, except those mentioned in Section 5.1 of this document. In addition, a BIS for IDRP for SIP shall implement: - an interface to the SIP protocol described in section 5.2.1 of this document - the ability to identify and extract SIP reachability and SIP forwarding information as described in section 5.2.2 of this document - SIP packet forwarding functions described in section 5.2.6 of this document - domain configuration information listed in section 5.2.5 of this document - the advertisement of SIP address information in NLRI as described in section 5.3 of this document Expiration Date April 1994 [Page 6] - 7 - 5.2.1 Exchanging IDRP information between SIP-only routers. IDRP assumes pair-wise communication between participating BISs. IDRP information is carried between a pair of BISs in the form of BISPDUs. In the case of IDRP for SIP, these BISPDUs are carried in the data field of SIP packets of protocol type %%TBD%%. If a domain doesn't support SIP internally (some of the routers within the domain are not SIP-capable), then SIP packets carrying BISPDU shall be carried accross the domain using IPAE [8]. 5.2.2 Identifying SIP reachability and SIP forwarding information NLRI passed by the UPDATE PDU has an indication of the protocol family for the destinations depicted by the NLRI. The indication is encoded in the Proto_type, Proto_length and Protocol fields. An implementation of IDRP for SIP shall have the following values in the NLRI: Proto_Type: 1 (ISO/IEC TR 9577 IPI/SPI) Proto_Length: 6 Protocol: hexadecimal "80:00:00:00:86:DD" Addr_Length: variable (the value shall be between 2 and 64) Addr_Info: SIP address prefixes, encoded in binary, as follows: This is a variable length field that contains a list of SIP address prefixes for the routes that are being advertised. Each SIP address prefix is encoded as a 2-tuple of the form , 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 SIP Expiration Date April 1994 [Page 7] - 8 - address prefix. A length of zero indicates a prefix that matches all SIP addresses (with prefix, itself, of zero octets). b) Prefix: The Prefix field contains SIP 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. An implementation of IDRP for SIP shall ignore any NLRI indicating a different protocol type. The NEXT_HOP attribute in the UPDATE PDU also has a Proto_type, Proto_Length and Protocol fields which indicate the protocol family for the address of the NEXT_HOP. An implementation of IDRP for SIP shall have the following values in the NEXT_HOP field: Proto_Type: 1 (ISO/IEC TR 9577 IPI/SPI) Proto_Length: 6 Protocol: hexadecimal "80:00:00:00:86:DD" Length of NET: 8 NET of Next Hop: a SIP address, encoded in binary SNPA information: as appropriate for the subnetwork type in use An implementation of IDRP for SIP shall ignore any NEXT_HOP information indicating a different protocol type. Note that the Protocol component of the NLRI field and the NEXT_HOP field consists of the IPI/SPI indicating an IEEE 802.1a SNAP header followed by the IEEE 802.1a SNAP header itself. 5.2.3 Mapping between SIP Type Of Service parameters and IDRP Distinguishing Attributes. SIP defines four distinct Type of Service (TOS) Parameters: - minimize delay Expiration Date April 1994 [Page 8] - 9 - - maximize throughput - maximize reliability - minimize monetary cost A SIP packet can carry at most one of the above TOSs in its Flow Label field. Therefore, a RIB in IDRP for SIP can have at most one Distinguishing Attribute. IDRP for SIP supports the following Distinguishing Attributes: - Transit Delay - Residual Error - Expense A conformant implementation is required to recognize these attributes when received from an adjacent BIS. A SIP-derived Distinguishing Attribute is defined as the TOS parameter extracted from a SIP packet that needs to be forwarded by a BIS. The mapping between the SIP-derived Distinguishing Attribute and a RIB-Att is defined as follows: SIP ToS IDRP Distinguishing Attribute ------- ----------------------------- minimize delay Transit Delay maximize reliability Residual Error minimize monetary cost Expense maximize throughput default 5.2.4 Confederations of domains. IDRP supports the ability to group Routing Domains into a Routing Domain Confederation. Likewise, IDRP for SIP supports the ability to group a collection of domains into a Confederation of domains. Expiration Date April 1994 [Page 9] - 10 - 5.2.5 Domain Configuration Information Correct Operation of IDRP described in [1] 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 SIP protocol is: a) Location and identity of adjacent Intra-Domain ISs (routers) The MIB table INTRA-IS lists the SIP 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 INTRA-IS 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 SIP address of the local BIS will be listed in the INTRA-IS table. b) 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 INTERNAL-BIS, which contains a set of SIP addresses which identify the BISs in the domain. c) Location and identity of BISs in adjacent domains: Each BIS needs information to identify the SIP 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 EXTERNAL-BIS-NEIGHBORS, which is a table of SIP addresses. d) SIP 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 INTERNAL-SYSTEMS. The SIP network address information shall be expressed in terms of SIP address prefixes. A single prefix can be used to describe: Expiration Date April 1994 [Page 10] - 11 - - a host address, - a subnetwork number, - a network number, or - a collection of contiguous network numbers e) LOCAL RDI This information is contained in managed object LOCAL-RDI; it is the RDI of the routing domain in which the BIS is located. As specified in section 7 of this document, the RDI for an IDRP for SIP routing domain has an NSAP Address format. This NSAP Address format is built out of a fixed "header" and the domain identifier of this routing domain. f) RIB-AttSet The RIB-AttSet contains information about the QoS functions a BIS will support. As described in section 4, this shall be empty. g) 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 RDC-Config. Each RDC is identified by an RDI which has the format described in section 7 of this document. 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. h) Local SIP addresses The LOCAL SIP MIB table contains a list of SIP addresses assigned to the interfaces of a BIS. This information is used to determine what interface should be used to forward outgoing NPDUs. 5.2.6 Forwarding of SIP packets This section is intended to define the same function for SIP Expiration Date April 1994 [Page 11] - 12 - packets as is defined for CLNP packets in the "Forwarding Process for CLNS" (Section 8 in [1]). It is assumed that a BIS is capable of distinguishing between a FIB constructed by means of an intra-domain routing protocol and a FIB constructed by means of IDRP. After a BIS determines the packet's destination SIP address, the BIS shall proceed as follows: a) If the destination address depicts a system located within the domain of the receiving BIS, then the BIS shall forward the SIP packet to any of the ISs listed in the managed object INTRA-IS. That is, any further forwarding of the SIP packet is the responsibility of the intra-domain routing protocol; otherwise, b) the destination system is located in a different domain, and the local BIS shall perform the following actions: It shall determine the SIP-Derived Distinguishing Attribute, according to clause 5.2.3. It shall next apply the procedures of clause 5.2.3 to determine if the SIP-Derived Distinguishing Attribute matches any of the RIB-Atts of the information base(s) supported by the local BIS. If such a match is found, then the FIB with the matched RIB-Atts is used for forwarding. If the procedures of clause 5.2.3 identify a non-default SIP- Derived Distinguishing Attribute, but the local BIS does not maintain a FIB with the matching RIB-Atts, or the local BIS maintains a FIB with the matching RIB-Atts but this FIB does not have a route to the destination, then the local system sets the ToS bits in the Flow Label field of the SIP packet to 0 and uses FIB with no Distinguishing Attributes. The incoming SIP packet shall be forwarded based on the FIB entry that has the longest SIP address prefix that matches the destination of the incoming SIP packet, as follows: 1) If the entry in the inter-domain FIB that corresponds to the destination address of an incoming SIP packet contains a NEXT_HOP that identifies an interface of a BIS such that the interface is attached to a subnet shared with the local BIS, then the SIP packet shall be forwarded directly to the BIS indicated in the NEXT_HOP entry over that interface; otherwise, 2) if the entry in the inter-domain FIB that corresponds to the destination address of the incoming SIP packet contains a NEXT_HOP entry that identifies an interface of a BIS such Expiration Date April 1994 [Page 12] - 13 - that the interface is not attached to any of the subnets attached to the local BIS, then the local BIS has the following options: i) Encapsulate the SIP packet The local BIS may encapsulate the SIP packet, using IPAE with its own IP address as the source address and the IP address of the next-hop BIS contained in the NEXT_HOP entry as the destination address. ii) Use paths calculated by the intra-domain routing protocols The local BIS may query the FIB constructed by the intra-domain routing protocols to ascertain if that FIB contains a route to the destination system. If that is the case, and if the path constructed by the intra-domain routing protocols delivers the SIP packet to the appropriate next-hop BIS, then the SIP packet may be forwarded using the FIB constructed by the intra-domain routing protocols. ITEM Questions/Features Refer. Status Support ---------------------------------------------------------------- IP_EXTFWD Does the BIS correctly forward 5.3 M Yes___ SIP packets with destinations outside its routing domain? IP_INTFWD Does the BIS correctly forward 5.3 M Yes___ SIP packets with destinations inside its routing domain? --------------------------------------------------------------- Table 1: PICS Proforma for IDRP: SIP packet forwarding Expiration Date April 1994 [Page 13] - 14 - The "ITEM" column describes the feature in the SIP forwarding function that the IDRP implementation is to provide. The "Question/Feature" section seeks to describe the feature. The Reference is the section in this document that describes this feature. The status gives an indication of "M" - Mandatory feature for an IDRP implementation or "O" - optional feature. The "Support" column is a column for the implementor to check whether this feature is available in a particular implementation.) 5.3 Advertising NLRI information for SIP addresses The NLRI field in an UPDATE PDU contains SIP address information about systems that reside within a given routing domain or whose SIP address space is under the control of the administrator of the routing domain. It should not be used to convey information about the operational status of these systems. The information in the NLRI field is intended to convey static administrative information rather than dynamic transient information; for example, it is not necessary to report that a given system has changed from offline to online. End systems (hosts) and Intermediate systems (routers) within a RD using IDRP may use any SIP address that is valid within the SIP context. Within the NLRI, the address information for a set of SIP addresses may be represented by a SIP prefix. A SIP prefix is the sequence of bits in a 8 byte SIP address which are common between a set of SIP addresses. For example, the addresses 4005:0000:0000:0000 through 4005:FFFF:FFFF:FFFF have the first 16 bits of the address information in common. These 16 bits of the SIP address may be called a SIP prefix which represents the set of SIP addresses 4005:0000:0000:0000 through 4005:FFFF:FFFF:FFFF. A SIP prefix must contain a contiguous set of bits starting at the most significant bit, but the bits may cover any part of the 8 byte SIP address. The following guidelines for inclusion of SIP address prefixes in the NLRI field of the UPDATE PDUs originated within a routing domain will provide efficient use of this protocol: a) Only SIP prefixes representing SIP addresses that are within the control of the Administrator of a given routing domain may be reported in the NLRI field for a RD. These SIP prefixes can represent SIP addresses for systems which are: - online, - offline, or Expiration Date April 1994 [Page 14] - 15 - - allocated to the network, but not yet allocated to a machine. b) SIP prefixes representing SIP addresses outside of the RD administrator's control shall not be included in the NLRI. c) For efficient use of the protocol, the WITHDRAW ROUTES field should not be used to report the NLRI of systems that are offline. This field should be used only to advertise SIP prefixes for SIP addresses that are no longer under the control of the administrator of the local routing domain, regardless of whether the systems are online or offline. A conformant implementation is required to have the ability to specify when an aggregated route may be generated out of partial routing information. A BIS at the border of a domain (or group of domains) must be able to generate an aggregated route for a whole set of NLRIs over which is has administrative control, even when not all of them are reachable at the same time. 6 Determining the forwarding address (Next Hop) NEXT_HOP 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, it shall be derived from the source SIP address of the SIP packet that carries the UPDATE BISPDU containing the route. 7 Routing Domain Identifiers used for both SIP and OSI Routing Domain Identifiers (RDIs) are identifiers used in BISPDUs to uniquely identify individual routing domains and routing domain confederations. An RDI of a pure SIP domain should be constructed as a concatenation of a unique NSAP address prefix 47:00:05:c0:02 and the unique identifier taken out of the SIP address space. While the unique identifier is just a number which identifies the routing domain, and need not bear any relationship to any reachable addresses within the domain, using the cluster identifier of one of the networks belonging to the routing domain may potentially offer some advantages. Alternatively an RDI of a SIP domain can be constructed by a concatenation of a unique NSAP address prefix assigned by a valid Expiration Date April 1994 [Page 15] - 16 - addressing authority and an appropriately assigned autonomous system number as follows: 47:00:05:c0:01:aa:aa where 47:00:05:c0:01 is a unique NSAP prefix, and aa.aa is the autonomous system number. 8 Deployment Guidelines for IDRP for SIP The correct and efficient operation of the IDRP protocol requires that certain guidelines are used for deployment with ISO routing Domains. Some equivalent deployment guidelines for IDRP for SIP are required within domains. These guidelines represent only the required deployment guidelines, and not details on the usage of IDRP for SIP in the Internet. 8.1 Minimum configuration of a domain A domain using IDRP for SIP must as a minimum contain: - one BIS, and - one BIS capable of delivering NPDUs to the intra-domain routing function if the domain contains hosts. 8.2 Multiple IDRP sessions between the same pair of routers A SIP router may have multiple SIP 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, a SIP router may potentially have multiple IDRP sessions with another router, since each BIS may have multiple SIP addresses, and one BIS may not be able to ascertain that those addresses correspond to the same BIS. Multiple IDRP sessions between SIP BISs may not be efficient, but they are not illegal, nor do they impact the robustness of the IDRP for SIP 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 Expiration Date April 1994 [Page 16] - 17 - within a single domain is to bind all source addresses of outgoing BISPDUs to the SIP address of a particular interface 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. 9. 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 [1]). 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: 1. 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 SIP 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. 2. IDRP implementations should allow a domain to prefer a particular path to a destination (when more than one path is available). This function may be implemented by allowing system administrators to assign "weights" to domain identifiers, and by having the route selection process select a route with the lowest "weight" (where "weight" of a route is defined as a sum of "weights" of all domains in the RD_PATH path attribute associated with that route). 3. IDRP implementations should allow a domain to ignore routes with certain domains in the RD_PATH path attribute. Such function can be implemented by using the technique outlined in [10], and by assigning "infinity" as "weights" for such domains. The route selection process must ignore routes that have "weight" equal to "infinity". Expiration Date April 1994 [Page 17] - 18 - 10 Security Considerations Security issues are not discussed in this document. 11. Acknowledgements We would like to acknowledge comments from Christian Huitema and Steve Deering. 12. References [1] ISO/IEC IS 10747 - Information Processing Systems - Telecommunications and Information Exchange between Systems - Protocol for Exchange of Inter-domain Routeing Information among Intermediate Systems to Support Forwarding of ISO 8473 PDUs, 1993. [2] Hares, S., "IDRP Document Family Tree", Internet Draft [3] ISO 8473 - Information Processing Systems - Data Communications - Protocol for Providing the Connectionless-mode Network Service, 1988. [4] ISO/IEC 10589 - Information Processing Systems - Telecommunications and Information Exchange between systems - Intermediate System to Intermediate System Intra-Domain routeing information exchange protocol for use in conjunction with the Protocol for providing the Connectionless-mode Network Service (ISO 8473), 1992. [5] ISO 9542 - Information Processing Systems - Telecommunications and information exchange between systems - End system to Intermediate system routeing exchange protocol for use in conjunction with the Protocol for providing the connectionless-mode network service (ISO 8473) [6] Deering, S., "Simple Internet Protocol (SIP) Specification", Internet Draft November 1992 [7] Braun, H-W., "Models of Policy Based Routing", RFC 1104, Merit/NSFNET, June 1989. [8] Crocker, D., Hinden, B., "IP Address Encapsulation (IPAE): A Mechanism for Introducing a New IP", Internet Draft, November 1992 Expiration Date April 1994 [Page 18] - 19 - Authors' Addresses Susan Hares Merit, Inc 1071 Beal Avenue Ann Arbor, MI 4810x Phone: (313)936-2095 Email: skh@merit.edu Expiration Date April 1994 [Page 19]