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Network Working Group                                        K. MurakamiRequest for Comments: 2176                                   M. MaruyamaCategory: Informational                                 NTT Laboratories                                                               June 1997IPv4 over MAPOS Version 1Status of this Memo   This memo provides information for the Internet community.  This memo   does not specify an Internet standard of any kind.  Distribution of   this memo is unlimited.Authors' 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.Murakami & Maruyama          Informational                      [Page 1]

RFC 2176                         MAPOS                         June 19972. 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 0x0021 (hexadecimal) as   defined by the "MAPOS Version 1 Assigned Numbers" [4].  The   information field contains the IP datagram.   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          Informational                      [Page 2]

RFC 2176                         MAPOS                         June 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     assigned by IANA [6].     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.Murakami & Maruyama          Informational                      [Page 3]

RFC 2176                         MAPOS                         June 1997     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.     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 [7].  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    :       IP address of the node     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     assigned by IANA [6].     Operation Code (16 bits)     The operation code is 23 for MAPOS-UNARP in Decimal as assigned by     IANA [6].Murakami & Maruyama          Informational                      [Page 4]

RFC 2176                         MAPOS                         June 1997   The node MUST send three UNARP packets at 30 seconds intervals.  The   receiving node of the packet MUST clear the ARP cache entry   associated with the Sender Protocol (IP) Address, if and only if the   corresponding Hardware (HDLC) Address is not equal to that contained   in the UNARP packet.  That is, if both the Sender Hardware (HDLC)   Address and the Sender Protocol(IP) Address match those of the cached   entry, the entry is left unchanged.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 [8].  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.   Furthermore, when the link is lost on an interface, all ARP cache   entries associated with the interface MUST be removed immediately.   Causes for link loss includes conditions such as loss of carrier and   out-of-synchronization.3.5 IP Broadcast and multicast   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 [9].  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.Murakami & Maruyama          Informational                      [Page 5]

RFC 2176                         MAPOS                         June 1997References   [1]   Murakami, K. and M. Maruyama, "MAPOS - Multiple Access Protocol         over SONET/SDH, Version 1,"RFC-2171, June 1997.   [2]   Simpson, W., editor, "PPP in HDLC-like Framing,"RFC-1662,         July 1994.   [3]   Postel, J., "Internet Protocol (IP),"RFC-791, September 1981.   [4]   Maruyama, M. and K. Murakami, "MAPOS Version 1 Assigned         Numbers,"RFC-2172, June 1997.   [5]   Mogul, J. and S. Deering, "Path MTU Discovery,"RFC-1191,         Nov. 1990.   [6]   IANA, "IANA-Assignments",http://www.iana.org/iana/assignments.html   [7]   Malkin, G., "ARP Extension - UNARP,"RFC-1868, November 1995.   [8]   Braden, R., "Requirements for Internet Hosts - Communication         Layers,"RFC-1122, October 1989.   [9]   Deering, S., "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     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.netMurakami & Maruyama          Informational                      [Page 6]