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diff --git a/doc/rfc/rfc895.txt b/doc/rfc/rfc895.txt new file mode 100644 index 0000000..2a82319 --- /dev/null +++ b/doc/rfc/rfc895.txt @@ -0,0 +1,171 @@ + + +Network Working Group Jon Postel +Request for Comments: 895 ISI + April 1984 + + A Standard for the Transmission of IP Datagrams + over Experimental Ethernet Networks + + +Status of this Memo + + This RFC specifies a standard method of encapsulating Internet + Protocol (IP) [1] datagrams on an Experimental Ethernet [2]. This + RFC specifies a standard protocol for the ARPA Internet community. + +Introduction + + This memo applies to the Experimental Ethernet (3-megabit/second, + 8-bit addresses). The procedure for transmission of IP datagrams on + the Ethernet (10-megabit/second, 48-bit addresses) is described in + [3]. + +Frame Format + + IP datagrams are transmitted in standard Experimental Ethernet + frames. The type field of the Ethernet frame must contain the value + 513 (1001 octal). The data field contains the IP header followed + immediately by the IP data. + + If necessary, the data field should be padded to meet the + Experimental Ethernet minimum frame size. This padding is not part + of the IP packet and is not included in the total length field of the + IP header. + + The maximum length of an IP datagram sent over an Experimental + Ethernet is 1536 octets. Implementations are encouraged to support + full-length packets. Gateway implementations MUST be prepared to + accept full-length packets and fragment them if necessary. If a + system cannot receive full-length packets, it should take steps to + discourage others from sending them, such as using the TCP Maximum + Segment Size option [4]. + + Note: Datagrams on the Ethernet may be longer than the general + Internet default maximum packet size of 576 octets. Hosts connected + to an Ethernet should keep this in mind when sending datagrams to + hosts not on the same Ethernet. It may be appropriate to send + smaller datagrams to avoid unnecessary fragmentation at intermediate + gateways. Please see [4] for further information on this point. + + + + + + +Postel [Page 1] + + + +RFC 895 April 1984 + + +Address Mappings + + The mapping between 32-bit Internet addresses to 8-bit Experimental + Ethernet addresses can be done several ways. + + The easiest thing to do is to use the last eight bits of host number + part of the Internet address as the host's address on the + Experimental Ethernet. This is the recommended approach. + + Broadcast Address + + The broadcast Internet address (the address on that network with a + host part of all binary ones) should be mapped to the broadcast + Experimental Ethernet address (address zero). + +Trailer Formats + + Some versions of Unix 4.2bsd use a different encapsulation method in + order to get better network performance with the VAX virtual memory + architecture. Consenting systems on the same Ethernet may use this + format between themselves. + + No host is required to implement it, and no datagrams in this format + should be sent to any host unless the sender has positive knowledge + that the recipient will be able to interpret them. Details of the + trailer encapsulation may be found in [6]. + + (Note: At the present time Unix 4.2bsd will either always use + trailers or never use them (per interface), depending on a boot-time + option. This is expected to be changed in the future. Unix 4.2bsd + also uses a non-standard Internet broadcast address with a host part + of all zeroes, this will also be changed in the future.) + +Byte Order + + As described in Appendix B of the Internet Protocol + specification [1], the IP datagram is transmitted over the Ethernet + as a series of 8-bit bytes. + + + + + + + + + + + + +Postel [Page 2] + + + +RFC 895 April 1984 + + +References + + [1] Postel, J., "Internet Protocol", RFC-791, USC/Information + Sciences Institute, September 1981. + + [2] Metcalfe, R. and D. Boggs, "Ethernet: Distributed Packet + Switching for Local Computer Networks", Communications of the ACM, + V.19, N.7, pp 395-402, July 1976. + + [3] Hornig, C., "A Standard for the Transmission of IP Datagrams + over Ethernet Networks", RFC-894, Symbolics Cambridge Research + Center, April 1984. + + [4] Postel, J., "The TCP Maximum Segment Size Option and Related + Topics", RFC-879, USC/Information Sciences Institute, November 1983. + + [5] Plummer, D., "An Ethernet Address Resolution Protocol", RFC-826, + Symbolics Cambridge Research Center, November 1982. + + [6] Leffler, S., and M. Karels, "Trailer Encapsulations", RFC-893, + University of California at Berkeley, April 1984. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Postel [Page 3] + |