Though our discussion has been aimed mainly at future improvements required to raise the Internet MTU, there are several existing standards that support MTUs larger than 1,500 bytes, and can each be used for your private network.
The following list includes most of these technologies, along with references to their specifications :

• FDDI IP MTU of 4352 bytes (per RFC1390)/4470 bytes (in practice).
  FDDI lost its market share to Fast Ethernet. This battle was not a won on a technical merit - FDDI being resilient and supporting higher throughput through large MTU. FDDI upgrades and maintenance are more difficult and more expensive than Fast Ethernet's.
• Standard POS links (RFC2615) with 16 bit CRCs typically have maximum receive unit (MRU) values of 4470; with CRC-32, 9180 octets.
• ATM (Cisco default of 4470, 9180 per RFC2225)
• Fibre Channel (RFC2625): 65,280, etc.
• Token Ring supports 4k frames at 4 Mbps operation (RFC1042), and 18k frames at 16 and 100 Mbps operation (IBM).
  Token ring's market share has always been lagging behind Ethernet's, although it was well known that Token Ring performed better at higher netwok load conditions. Ethernet's momentum has driven equipment prices down. It is unlikely that High Speed Token Ring, Fast Ethernet's counter part, or the upcoming Gigabit Token Ring will gain market share. Large MTU capability was not enough to provide the competitive edge for Token Ring.
• HIPPI (High Performance Parallel Interface - RFC1374): With regard to IP over HIPPI, the maximum frame length will be exactly 64Kbytes, which allows for an IP payload of 65280 bytes.