A Standard for the Transmission of IP Datagrams over Ethernet Networks
also
- std-41
Extracted elements (14)
ARP dynamic discovery is strongly recommended over static tables for IP-to-Ethernet address mapping because Internet addresses are assigned arbitrarily on some networks, making static tables difficult to maintain.
Trailer encapsulation (used by Unix 4.2bsd) is a non-standard method intended to improve network performance with the VAX virtual memory architecture, but is explicitly not required and should not be used unless both sender and receiver support it.
Datagrams on Ethernet may be longer than the general Internet default maximum packet size of 576 octets. Hosts on Ethernet should consider sending smaller datagrams to avoid unnecessary fragmentation at intermediate gateways when communicating with hosts on other networks.
Implementations are encouraged to support full-length packets. Systems that cannot receive full-length packets should use mechanisms such as the TCP Maximum Segment Size option to discourage others from sending them.
Some Unix 4.2bsd systems use a trailer encapsulation method for better performance with VAX virtual memory architecture. No host is required to implement it, and datagrams in trailer format must not be sent to a host unless the sender has positive knowledge the recipient can interpret them.
Each host's implementation must know its own Internet address and respond to Ethernet Address Resolution packets appropriately, and should use ARP to translate Internet addresses to Ethernet addresses when needed.
Gateway implementations MUST be prepared to accept full-length packets (up to 1500 octets) and fragment them if necessary.
The broadcast Internet address (host part of all binary ones) should be mapped to the broadcast Ethernet address FF-FF-FF-FF-FF-FF hex.
The type field of the Ethernet frame MUST contain the value hexadecimal 0800 for IP datagrams.
IP-to-Ethernet address mapping may be accomplished via static tables (maintained per-host for all local hosts) or dynamic discovery via ARP. The use of ARP dynamic discovery is strongly recommended.
IP datagrams are transmitted in standard Ethernet frames with the type field set to hexadecimal 0800. The data field contains the IP header followed immediately by the IP data.
The IP datagram is transmitted over Ethernet as a series of 8-bit bytes, as described in Appendix B of RFC-791.
The maximum length of the Ethernet data field is 1500 octets, thus the maximum length of an IP datagram sent over an Ethernet is 1500 octets.
The minimum length of the Ethernet data field is 46 octets; if necessary, the data field should be padded with zero octets to meet the Ethernet minimum frame size. This padding is not part of the IP packet and is not included in the IP header total length field.