Need info about JUMBO frame

[Stefan09]

What is actually a JUMBO frame? Does it standardised? How a L2 switch accept JUMBO frame, when an ethernet frame size (maximum) can never exceed 1522 as per IEEE 802.Q ? thanks for your suggestions guys

[Marlon]

Jumbo frames are Ethernet frames with more than 1,500 bytes of payload. Conventionally, jumbo frames can carry up to 9,000 bytes of payload. Why 9000? because ethernet uses a 32 bit CRC that loses its effectiveness above about 12000 bytes. Many Gigabit Ethernet switches and Gigabit Ethernet network interface cards support jumbo frames. You can partition a logical network in which systems can exchange Jumbo Frames and mark them with IEEE 802.1Q virtual LAN tags. The extended frames will be transparent to the rest of the network. Adapters that implement IEEE 802.1Q can support different Ethernet frame sizes for different logical network interfaces. For example, a server could communicate with another server using Jumbo Frames while communicating with clients sitting on another VLAN or IP subnet using standard Ethernet frames - all via the same physical connection.

[DAIJIRO]

Ethernet has used 1500 byte frame sizes since it was created (around 1980). To maintain backward compatibility, 100 Mbps ethernet used the same size, and today "standard" gigabit ethernet is also using 1500 byte frames. This is so a packet to/from any combination of 10/100/1000 Mbps ethernet devices can be handled without any layer two fragmentation or reassembly. "Jumbo frames" extends ethernet to 9000 bytes. Why 9000? First because ethernet uses a 32 bit CRC that loses its effectiveness above about 12000 bytes. And secondly, 9000 was large enough to carry an 8 KB application datagram (e.g. NFS) plus packet header overhead. Is 9000 bytes enough? It's a lot better than 1500, but for pure performance reasons there is little reason to stop there. At 64 KB we reach the limit of an IPv4 datagram, while IPv6 allows for packets up to 4 GB in size. For ethernet however, the 32 bit CRC limit is hard to change, so don't expect to see ethernet frame sizes above 9000 bytes anytime soon.

[Steve123]

What is actually a JUMBO frame? Does it standardised? How a L2 switch accept JUMBO frame, when an ethernet frame size (maximum) can never exceed 1522 as per IEEE 802.Q ? thanks for your suggestions guys

That's because jumbo frames are not standard. However, if you use the "type" format, there's no reason in principle why the frame size can't grow beyond 1522 bytes. Of course, all switches in the path must be aware of the possibility of these jumbo frames.

[Shen]

Jumbo Frame support is designed to the enhance Ethernet networking throughput and significantly reduce the CPU utilization of large file transfers like large multimedia files or large data files by enabling more efficient larger payloads per packet. By sending larger payloads per packet, fewer packets need to be routed, reducing the overhead on the CPU and potentially improving networking throughput.

Jumbo Frame support in Sun's Gigabit Ethernet Network Interface cards allows the sending and receiving of jumbo frame size packets which are up to 6 times the size of standard Ethernet packets. Jumbo Frame delivers up to 9216 byte packets instead of a 1522 byte packet for standard Ethernet, which consists of a 1500 byte payload + 14 bytes for header + VLAN tag 4 bytes + CRC 4 bytes.

Key Features:

• Supports up to 9K bytes MTU (Maximum Transfer Unit)
• VLAN containment (MTU specified in a per VLAN basis in addition to per card basis)
• Jumbo Frame, once set, remains persistent through reboots
• Jumbo Frame can be disabled on the fly without reboot

[Big Fish]

What is actually a JUMBO frame? Does it standardised? How a L2 switch accept JUMBO frame, when an ethernet frame size (maximum) can never exceed 1522 as per IEEE 802.Q ? thanks for your suggestions guys

There is no "de jure" standard for the size of a "jumbo frame" as the IEEE has not seen fit to create one. One can argue though that the "de facto" standard for the jumbo frame is such that it results in an IPv4 MTU of 9000 bytes or more based on that being what Alteon used in their GbE NICs which IIRC were among if not the first to have a "jumbo frame" in the Ethernet space.

[Zachary]

There is no "de jure" standard for the size of a "jumbo frame" as the IEEE has not seen fit to create one. One can argue though that the "de facto" standard for the jumbo frame is such that it results in an IPv4 MTU of 9000 bytes or more based on that being what Alteon used in their GbE NICs which IIRC were among if not the first to have a "jumbo frame" in the Ethernet space.

Agreed, although i have seen "jumbo" on 100 Mbps as well, although cannot remember where, and it has spread to 10G as well.

A Cisco Cat 6500 could even have more than 1 different jumbo limits, just on different blades if you had various vintages of equipment.

and the telecomms suppliers do not agree about 9000 bytes:

• some Marconi SDH kit calls 4000+ bytes "jumbo".
• and DWDM kit often works happily at 64 Kbytes since they dont even
• worry about packet boundaries.

and then there is "baby jumbo" which is more than standard 1514 / 1518, but usually less than 1600 or 2000 bytes.......