# Jumbogram

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{{Short description|Large packets in IPv6}}
{{primary sources|date=May 2015}}
{{Use American English|date = March 2019}}

In [packet-switched](/source/packet_switched) computer networks, a '''jumbogram''' ([portmanteau](/source/portmanteau) of ''jumbo'' and ''[datagram](/source/datagram)'') is an [internet-layer](/source/internet-layer) packet exceeding the standard [maximum transmission unit](/source/maximum_transmission_unit) (MTU) of the underlying network technology. In contrast, large packets for ''[link-layer](/source/link-layer)'' technologies are referred to as [jumbo frame](/source/jumbo_frame)s.

The Total Length field of [IPv4](/source/IPv4) and the Payload Length field of [IPv6](/source/IPv6) each have a size of 16 bits, thus allowing data of up to {{gaps|65|535|[octet](/source/octet_(computing))s}}. This theoretical limit for the [Internet Protocol](/source/Internet_Protocol) (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](/source/IPv6_packet) carrying a [payload](/source/payload_(computing)) larger than {{gaps|65|535|octets}}.<ref name=rfc2675>{{cite IETF |author1=Borman, D. |author2-link=Steve Deering |author2=Deering, S. |author3=Hinden, R. |date=August 1999 |title=IPv6 Jumbograms |publisher=[IETF](/source/Internet_Engineering_Task_Force) |RFC=2675}}</ref>

==IPv6 jumbograms==
An optional feature of IPv6, the [''jumbo payload'' option](/source/IPv6_packet), allows the exchange of packets with payloads of up to one byte less than 4 [GiB](/source/GiB) (2<sup>32</sup> − 1 = 4,294,967,295 bytes), by making use of a 32-bit length field. Historically, [transport layer](/source/transport_layer) protocols, such as the [Transmission Control Protocol](/source/Transmission_Control_Protocol) (TCP) and the [User Datagram Protocol](/source/User_Datagram_Protocol) (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.<ref name=rfc2675 />  Since after a number of years IPv6 jumbograms have not been widely deployed, some have proposed their removal from the standards.<ref>{{Cite ietf |last1=Jones |first1=T. |last2=Fairhurst |first2=G. |date=2019-05-08 |title=Change Status of RFC 2675 to Historic |draft=draft-jones-6man-historic-rfc2675-00.html |access-date=2021-02-16 |language=en |publisher=Work in progress (an expired draft)}}</ref>

==See also==
*[Maximum Segment Size](/source/Maximum_Segment_Size) (MSS)

==References==
{{Reflist}}

Category:Packets (information technology)
Category:IPv6

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Adapted from the Wikipedia article [Jumbogram](https://en.wikipedia.org/wiki/Jumbogram) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Jumbogram?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.