In
packet-switched computer networks, a jumbogram (
portmanteau
A portmanteau word, or portmanteau (, ) is a blend of words[jumbo
Jumbo (about December 25, 1860 – September 15, 1885), also known as Jumbo the Elephant and Jumbo the Circus Elephant, was a 19th-century male African bush elephant born in Sudan. Jumbo was exported to Jardin des Plantes, a zoo in Paris, and t ...](_blank)
'' and ''
datagram
A datagram is a basic transfer unit associated with a packet-switched network. Datagrams are typically structured in header and payload sections. Datagrams provide a connectionless communication service across a packet-switched network. The del ...
'') is an
internet-layer packet exceeding the standard
maximum transmission unit
In computer networking, the maximum transmission unit (MTU) is the size of the largest protocol data unit (PDU) that can be communicated in a single network layer transaction. The MTU relates to, but is not identical to the maximum frame size tha ...
(MTU) of the underlying network technology. In contrast, large packets for ''
link-layer'' technologies are referred to as
jumbo frames.
The Total Length field of
IPv4 and the Payload Length field of
IPv6
Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv ...
each have a size of 16 bits, thus allowing data of up to . This theoretical limit for the
Internet Protocol
The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet.
...
(IP) MTU, however, is reached only on networks that have a suitable link layer infrastructure. While IPv4 has no facilities to exceed its theoretical IP MTU limit, the designers of IPv6 have provided a protocol extension to permit packets of larger size. Thus, in the context of IPv6, a jumbogram is understood as an
IPv6 packet carrying a
payload larger than .
IPv6 jumbograms
An optional feature of IPv6, the
''jumbo payload'' option, allows the exchange of packets with payloads of up to one byte less than 4
GiB
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
(2
32 − 1 = 4,294,967,295 bytes), by making use of a 32-bit length field. Historically,
transport layer
In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-end ...
protocols, such as the
Transmission Control Protocol
The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is common ...
(TCP) and the
User Datagram Protocol
In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network ...
(UDP), include data size parameters limited to only 16 bits (length, urgent data pointer). The support for IPv6 jumbograms required a redesign in all Transport Layer protocols. The ''jumbo payload'' option and the transport-layer modifications are described in RFC 2675.
Since after a number of years IPv6 jumbograms have not been widely deployed, some have proposed their removal from the standards.
See also
*
Maximum Segment Size (MSS)
References
{{Reflist
Packets (information technology)
IPv6