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Jumbo frames have payloads greater than 1500 bytes. In computer networking, jumbo frames are Ethernet frames with more than 1500 bytes of payload, the limit set by the IEEE 802.3 standard. [1] The payload limit for jumbo frames is variable: while 9000 bytes is the most commonly used limit, smaller and larger limits exist.
In Ethernet-based routers, MTU normally refers to the IP MTU. If jumbo frames are allowed in a network, the IP MTU should also be adjusted upwards to take advantage of this. Since the IP packet is carried by an Ethernet frame, the Ethernet frame has to be larger than the IP packet.
In packet-switched computer networks, a jumbogram (portmanteau of jumbo and datagram) is an internet-layer packet exceeding the standard maximum transmission unit (MTU) of the underlying network technology. In contrast, large packets for link-layer technologies are referred to as jumbo frames.
The receiver of the packet echoes the congestion indication to the sender, which reduces its transmission rate as if it detected a dropped packet. Rather than responding properly or ignoring the bits, some outdated or faulty network equipment has historically dropped or mangled packets that have ECN bits set.
The window scale value can be set from 0 (no shift) to 14 for each direction independently. Both sides must send the option in their SYN segments to enable window scaling in either direction. Some routers and packet firewalls rewrite the window scaling factor during a transmission.
Then, similar to IPv4, any device along the path whose MTU is smaller than the packet will drop the packet and send back an ICMPv6 Packet Too Big (Type 2) message containing its MTU, allowing the source host to reduce its path MTU appropriately. The process is repeated until the MTU is small enough to traverse the entire path without fragmentation.
ICMPv6 provides a minimal level of message integrity verification by the inclusion of a 16-bit checksum in its header. The checksum is calculated starting with a pseudo-header of IPv6 header fields according to the IPv6 standard, [6] which consists of the source and destination addresses, the packet length and the next header field, the latter of which is set to the value 58.
Jumbo frames and jumbograms are not to be confused with packet MTU, which is a physical-layer limitation (1518 bytes for ethernet). Large MTUs are defined per-vendor, and to use them violates 802.3, so it is very proprietary in implementation (though coincidentally usually compatible).