INTERNET-DRAFT EXPIRES OCTOBER 1997 INTERNET-DRAFT Network Working Group K. Murakami INTERNET-DRAFT M. Maruyama Category: Informational NTT Laboratories April 1997 IPv4 over MAPOS Version 1 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 and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Author's Note: This memo documents a mechanism for supporting Version 4 of the Internet Protocol (IPv4) on Version 1 of the Multiple Access Protocol over SONET/SDH. This document is NOT the product of an IETF working group nor is it a standards track document. It has not necessarily benefited from the widespread and in-depth community review that standards track documents receive. Abstract This document describes a protocol for transmission of the Internet Protocol Version 4 (IPv4) over Multiple Access Over SONET/SDH (MAPOS) version 1. MAPOS is a link layer protocol and provides multiple access capability over SONET/SDH links. IP runs on top of MAPOS. This document explains IP datagram encapsulation in HDLC frame of MAPOS, and the Address Resolution Protocol (ARP). 1. Introduction Multiple Access Protocol over SONET/SDH (MAPOS) [1] is a high-speed link-layer protocol that provides multiple access capability over SONET/SDH. Its frame format is based on the HDLC-like framing [2] for PPP. A component called ``Frame Switch'' [1] allows multiple nodes to be connected together in a star topology to form a LAN. Using long haul SONET/SDH links, the nodes on such a ``SONET-LAN'' can span over a wide geographical area. The Internet Protocol (IP) [3] datagrams are transmitted in MAPOS HDLC frames [1]. This document describes a protocol for transmission of IP datagrams over MAPOS version 1 [1]. It explains IP datagram encapsulation in HDLC frame of MAPOS, and ARP (Address Resolution Protocol) for mapping between IP address and HDLC address. 2. Frame Format for Encapsulating IP Datagrams An IP datagram is transmitted in a MAPOS HDLC frame. The protocol field of the frame must contain the value 0x21 (hexadecimal) as defined by the ``MAPOS Version 1 Assigned Numbers'' [4]. The information field contains the IP datagram. Murakami, Maruyama [Page 1] I/D IPv4 over MAPOS Version 1 April 1997 The information field may be one to 65,280 octets in length; the MTU(Maximum Transmission Unit) of MAPOS is 65,280 octets. Although the large MTU size can suppress the overhead of IP header processing, it may cause fragmentation anywhere along the path from the source to the destination and result in performance degradation. To cope with the issue, Path MTU discovery [5] may be used. 3. Address Mapping This section explains MAPOS ARP and the mapping of special addresses. 3.1 ARP cache Each node on a MAPOS network maintains an ``ARP cache'' that maps destination IP addresses to their corresponding 8-bit HDLC addresses. Entries are added to this cache either manually or by the Address Resolution Protocol described below. Entries are removed from this cache manually, by the UNARP mechanism, or by ARP cache validation mechanism. An implementation must provide a mechanism for manually adding or removing arbitrary ARP cache entries. 3.2 Address Resolution Protocol (ARP) This subsection describes MAPOS ARP protocol and its packet format. 3.2.1 Overview The MAPOS ARP is similar to that for ethernet. Prior to sending an IP datagram, the node must know the destination HDLC address corresponding to the destination IP address. When its ARP cache does not contain the corresponding entry, it uses ARP to translate the IP address to the HDLC address. That is, it broadcasts an ARP request containing the destination IP address. In response to the request, the node which has the IP address sends an ARP reply containing the HDLC address. The returned HDLC address is stored in the ARP cache. 3.2.2 ARP Frame Format The protocol field for an ARP frame must contain 0xFE01 (hexadecimal) as defined by the ``MAPOS Version 1 Assigned Numbers'' [4]. The information field contains the ARP packet as shown below. Murakami, Maruyama [Page 2] I/D IPv4 over MAPOS Version 1 April 1997 +-------------------------+------------------------+ | Hardware Address Space | Protocol Address Space | | (25:MAPOS) | (2048 in Dec) | | 16 bits | 16 bits | +------------+------------+------------------------+ | Hard Addr | Proto Addr | Operation Code | | Length (4) | Length (4) |(1:Request 2:Response) | | 8 bits | 8 bits | 16 bits | +------------+------------+------------------------+ | Sender HDLC Address 32 bits | +--------------------------------------------------+ | Sender IP Address 32 bits | +--------------------------------------------------+ | Target HDLC Address 32 bits | +--------------------------------------------------+ | Target IP Address 32 bits | +--------------------------------------------------+ Figure 5 ARP packet format Hardware Address Space (16 bits) The hardware address space for MAPOS ARP is 25 in Decimal as defined by the ``MAPOS Version 1 Assigned Numbers'' [4]. Protocol Address Space (16 bits) The protocol address space for IP is 2048 in Decimal. Hardware Address Length (8 bits) The hardware address length is 4. Protocol Address Length (8 bits) The protocol address length for IP is 4. Operation Code (16 bits) The operation code is 1 for request and 2 for response. Sender hardware (HDLC) Address (32 bits) Contains the sender's HDLC address in an ARP request, and the target HDLC address in an ARP response. The 8-bit HDLC address is placed in the least significant place of the 32-bit field. The remaining bits should be zero. Sender Protocol (IP) Address (32 bits) Contains the sender's IP address in an ARP request, and the target IP address in an ARP response. Murakami, Maruyama [Page 3] I/D IPv4 over MAPOS Version 1 April 1997 Target hardware (HDLC) Address (32 bits) Contains unknown target HDLC address (all zeros) in an ARP request, and sender's HDLC address in an ARP response. The 8-bit HDLC address is placed in the least significant place of the 32-bit field. The remaining bits should be zero. Target Protocol (IP) Address (32 bits) Contains the target IP address in an ARP request, and the sender's IP address in an ARP response. 3.3 UNARP An implementation MUST provide an UNARP mechanism to flush obsolete ARP cache entries. The mechanism is similar to the ARP extension described in [6]. When a node detects that its port has came up, it MUST broadcast an UNARP packet. It forces every other node to clear the obsolete ARP entry which was created by the node previously connected to the switch port. An UNARP is an ARP clear request with the following values: Hardware Address Space : 25 Protocol Address Space : 2048 Hardware Address Length : 4 Protocol Address Length : 4 Operation Code : 23 (MAPOS-UNARP) Sender hardware (HDLC) Address : HDLC address of the node Sender Protocol (IP) Address : 0.0.0.0 (unknown) Target hardware (HDLC) Address : all 1 Target Protocol (IP) Address : 255.255.255.255 (broadcast) Hardware Address Space (16 bits) The hardware address space for MAPOS ARP is 25 in Decimal as defined by the ``MAPOS Version 1 Assigned Numbers'' [4]. Operation Code (16 bits) The operation code is 23 for MAPOS-UNARP in Decimal as defined by the ``MAPOS Version 1 Assigned Numbers'' [4]. The receiving node of the packet MUST clear the ARP entry corresponding to the Sender Hardware (HDLC) Address. 3.4 ARP Cache Validation An implementation MUST provide a mechanism to remove out-of-date cache entries and it SHOULD provide options to configure the timeout value [7]. One approach is to periodically time-out the cache entries, even if they are in use. This approach involves ARP cache timeouts in the order of a minute or less. 3.5 IP Broadcast and multicast Murakami, Maruyama [Page 4] I/D IPv4 over MAPOS Version 1 April 1997 In broadcast and multicast frames, the most significant bit of the HDLC address must be 1 [1]. In addition, the least significant bit must always be 1 to indicate the end of the field [1]. In the case of IP broadcast, the remaining six bits of the HDLC address must be all 1s. That is, it should be mapped to the HDLC broadcast address 0xFF (hexadecimal). In the case of IP multicast, the remaining six bits of the HDLC address must contain the lowest-order six bits of the IP multicast group address. It resembles IP multicast extension for ethernet described in [8]. Exceptions arise when these six bits are either all zeros or all ones, in which case they should be altered to the bit sequence 111110. 4. Security Considerations Security issues are not discussed in this memo. References [1] K. Murakami and M. Maruyama, "MAPOS - Multiple Access Protocol over SONET/SDH, Version 1," April 1997. [2] W. Simpson, editor, "PPP in HDLC-like Framing," RFC-1662, July 1994. [3] J. Postel, "Internet Protocol (IP)," RFC-791, September 1981. [4] M. Maruyama and K. Murakami, "MAPOS Version 1 Assigned Numbers," April 1997. [5] J. Mogul and S. Deering, "Path MTU Discovery," RFC1191, Nov.1990 [6] G. Malkin, "ARP Extension - UNARP," RFC-1868, November 1995. [7] R. Braden, "Requirements for Internet Hosts - Communication Layers," RFC-1122, October 1989. [8] S. Deering, "Host Extensions for IP Multicasting," RFC-1112, August 1989. Acknowledgements The authors would like to acknowledge the contributions and thoughtful suggestions of John P. Mullaney, Clark Bremer, Masayuki Kobayashi, Paul Francis, Toshiaki Yoshida, and Takahiro Sajima. Author's Address Ken Murakami NTT Software Laboratories 3-9-11, Midori-cho Murakami, Maruyama [Page 5] I/D IPv4 over MAPOS Version 1 April 1997 Musashino-shi Tokyo-180, Japan E-mail: murakami@ntt-20.ecl.net Mitsuru Maruyama NTT Software Laboratories 3-9-11, Midori-cho Musashino-shi Tokyo-180, Japan E-mail: mitsuru@ntt-20.ecl.net Murakami, Maruyama [Page 6] INTERNET-DRAFT EXPIRES OCTOBER 1997 INTERNET-DRAFT