Jumbogram

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In packet-switching computer networks, a jumbogram is a packet that is larger than the usual size limit for a given technology. The term jumbogram is a portmanteau of jumbo and datagram.

[edit] Ethernet jumbograms

Standard Ethernet limits frames to a maximum size of 1518 octets. This limit consists of a 1500 octet payload and an 18 octet Ethernet header. This limitation was reasonable for standard 10 Mbit/s Ethernet and 100 Mbit/s Fast Ethernet. At faster data rates, however, such as Gigabit Ethernet (1 Gbit/s), per-frame overhead becomes noticeable.

Ethernet jumbograms, or more accurately Jumbo Frames, are Ethernet frames that are larger than the normal maximum of 1500 octets. Most Gigabit Ethernet hardware is able to send and receive frames as large as 8192 or 9000 octets.

Use of non-standard frame sizes can cause hard-to-debug interoperability problems, for example when network switches silently discard large frames. This is why the IEEE does not standardise any form of jumbogram for Ethernet networks.

[edit] IPv6 jumbograms

The packet size field of IPv4 and IPv6 has a size of 16 bits; hence, IP packets are limited to a maximum size of 64 KiB (= 2¹⁶ B). An optional feature of IPv6, the jumbo payload option, allows the exchange of packets larger than this size between cooperating hosts.

Since both TCP and UDP include fields limited to 16 bits (length, urgent data pointer), support for IPv6 jumbograms requires slight tweaks to the transport layer. Both the jumbo payload options and the transport-layer tweaks are described in RFC 2675.