Document Number TWG-1993 / 042 ________________________________________________________________ SOURCE: Novell, Inc. Jay E. Israel M/S F6-91-2 2275 Trade Zone Blvd. San Jose, CA 95131 Telephone: 408-473-8478 Fax: 408-435-1706 Email: jay@novell.com ________________________________________________________________ TYPE OF CONTRIBUTION: INFORMATIONAL SPECIFICATION ________________________________________________________________ ISSUE ADDRESSED: Transmission of Novell IPX Datagrams over the SMDS Service, Version 1.0 ________________________________________________________________ DATE: July 15, 1993 ________________________________________________________________ DISTRIBUTION: UNLIMITED ________________________________________________________________ Abstract This informational specification defines operation of Novell IPX- based protocols over Switched Multi-megabit Data Service (SMDS). ________________________________________________________________ SMDS Interest Group's Disclaimer "This is an Informational Specification which has been submitted by the originating organization for review and comment by members of the SIG TWG. However, the SIG TWG does not approve or disap- prove of any information contained in this document, nor can it provide assurance that its contents will not be revised in the future. Distribution of this Informational Specification is unlimited. Readers are advised to check with the originating organization for any possible updates to this document." ________________________________________________________________ 1. Scope This document defines implementation of Novell IPX-based Protocols over Switched Multi-megabit Data Service (SMDS). This information should be considered subject to change. This specification applies to the situations delimited in the following subsections. Future versions of this specification will expand the situations covered, as circumstances warrant. 1.1 The SMDS service provider supplies a separate virtual private network (VPN) to each separate administrative entity sub- scribing to an SMDS service. (Sometimes, this is called a "closed user group"; sometimes, a "logical subnetwork".) A VPN can carry IPX traffic, or other protocols, or multiple protocols concurrently, at the discretion of the SMDS subscriber. Stations within the same VPN access each other directly over SMDS. Stations of different VPNs access each other through a network- layer router. 1.2 Currently, two alternative routing protocols are specified for IPX: - RIP distance-vector routing [1], together with SAP (Service Advertising Protocol). SAP provides internetwork resource location. - NLSP link-state routing [2]. Since all packets are conveyed with IPX headers for both of these routing protocols, this specification supports them both. 1.3 An IPX router connected to SMDS may route between two (or more) VPNs. 2. Configurable values 2.1 Each point of attachment to SMDS has an eight-byte SMDS in- dividual station address (station_ia). This address is obtained from the SMDS service provider. 2.2 For each VPN, there is an eight-byte SMDS "global" group address (global_ga) signifying "all nodes belonging to the VPN, whether they use IPX, a different protocol, or multiple proto- cols." This address is obtained from the SMDS service provider. 2.3 For each VPN, there is an eight-byte SMDS "IPX" group address (ipx_ga) signifying "all nodes belonging to the VPN that use IPX." This address is obtained from the SMDS service provider. Implementations must allow that ipx_ga = global_ga. IPX broad- casts are sent to ipx_ga. 2.4 For each VPN, there is an eight-byte SMDS "IPX ARP Request" address (ipx_arp_ga). This address is obtained from the SMDS service provider. "ARP" refers to the Address Resolution Protocol specified in Reference [3]. Implementations must allow that the value of ipx_arp_ga be the same as the ARP request address used by other network-layer protocols. They must also allow that it be distinct. Typically, ipx_arp_ga = ipx_ga, and ipx_arp_ga is a group address. The value of ipx_arp_ga is con- figured separately so that in the future ARP replies may be pro- vided by a central service (rather than by the node owning the requested address), in which case ipx_arp_ga could become an individual (rather than a group) address. 2.5 For each VPN conveying NLSP, there is an eight-byte SMDS "NLSP group address" (ipx_nlsp_ga) used to convey the NLSP "multicast" packets specified in Reference [2]. This address is obtained from the SMDS service provider. Typically, ipx_nlsp_ga = ipx_ga, but implementations must allow the two to be different. 2.6 For each VPN, there is a four-byte IPX network number (ipx_net), assigned by the SMDS subscriber. 2.7 For each point of attachment to SMDS, there is a globally unique IEEE six-byte address (address_ieee). It is assigned by the manufacturer of the network interface device, from a range allocated by IEEE. The IEEE address should be readable program- matically from the device. [Note: if a station participates in more than one VPN through a single point of attachment, it is a local implementation choice to use either (a) the same address_ieee for all VPNs or (b) a different address_ieee for each VPN.] Though it is taken from the "MAC" address space, this value is not used by the data link layer. Rather, it is used as specified in Section 4 below. 2.8 For each VPN, there is a "maximum SMDS Interface Protocol Level 3 Service Data Unit (SDU) size" (L3sdu_max) assigned by the SMDS subscriber as a station configuration parameter. All stations participating in a VPN must use the same value of L3sdu_max. The value of L3sdu_max must be in the range 584 to 9188 (inclusive). Frames transmitted on SMDS must not have SMDS Level 3 SDU (that is, Level 3 user's information field [4]) larger than L3sdu_max bytes, including the eight bytes of 802.2 and SNAP header. 3. Packet Format Each IPX packet has the following format on SMDS: - three-level SMDS SIP header, - IEEE 802.2 LLC type 1 UI (Unnumbered Information) header, - five-byte IEEE 802.1A SNAP field, - IPX header as defined in [1], - IPX data, and - SMDS trailer. The PI field in the SMDS SIP L3_PDU header is 1 to indicate an encapsulated LLC frame [4]. The DSAP and SSAP of the LLC header contain AA (hexadecimal), indicating the presence of the SNAP field. The SNAP field con- tains 0000008137 (hexadecimal), indicating that the frame con- tains an IPX packet. 4. IPX Address Assignment An IPX network-layer address has three parts: - a four-byte network field, - a six-byte node field, and - a two-byte socket field. A router or NetWare server uses the configured value ipx_net (section 2.6) as the network number of a VPN. Other systems are not configured; they learn the network number by a protocol exchange with a router, as specified in Reference [1]. In the absence of a router, network number zero is used, meaning "the directly attached network." A station uses address_ieee (section 2.7) as its own IPX node number for the VPN with network number ipx_net in which it participates. Various socket values refer to different upper-layer entities within a station. 5. IPX Address Resolution The Address Resolution Protocol (ARP) specified in Reference [3] is used to determine the eight-byte SMDS destination address of an outgoing IPX packet. (Although Reference [3] is expressed in terms of Ethernet, its "Ethernet packet data" includes a variable-length hardware address, so it can be applied to eight- byte SMDS addresses as readily as to six-byte Ethernet addresses.) A station maintains a cache of ARP information to support assignment of the destination SMDS address to outgoing frames. The same ARP cache can be used to determine the six-byte IEEE source address of arriving frames. ARP packets are encapsulated in IEEE 802.2 LLC type 1 UI frames with SNAP. The SNAP field contains 0000000806 (hexadecimal), indicating that the frame contains an ARP packet. Certain parameters tailor ARP to a specific context. For IPX on SMDS, the following values are used: - The hardware type code for SMDS is 0E (hexadecimal). - The protocol type code for IPX is 8137 (hexadecimal). - The hardware address length for SMDS is eight. - The protocol address length for IPX is ten. - ARP requests are sent to the SMDS address ipx_arp_ga. The SMDS hardware addresses in ARP packets are in SMDS native address format, with the most significant bit of the Address Type sub-field as the high order bit of the first byte. The protocol address fields of ARP packets include the IPX net- work number followed by the node number. The bit order and byte order are the same as in the IPX header. 6. References [1] Novell, Inc., "IPX Router Specification," June 16, 1992, part number 107-000029-001. [2] Novell, Inc., "NetWare Link Services Protocol (NLSP) Specification," March 1993, part number 100-001708-001. [3] Plummer, D., "An Ethernet Address Resolution Protocol -- or -- Converting Network Protocol Addresses to 48.bit Ethernet Address for Transmission on Ethernet Hardware," RFC 826, November 1982. [4] Bellcore, "Generic System Requirements in Support of Switched Multi-megabit Data Service," Technical Reference TR-TSV-000772, Issue 1, May 1991. END OF SPECIFICATION Page 1