Hacker News Reader

Comment by suprjami | Hacker News Reader

"Jumbo frames" aren't any size. There is no standard. The standard is IEEE 802.3 1518 byte frames. Anything larger is a non-standardized agreement between link partners on a broadcast domain.

There are NICs which only support 4K frames. Those are also "jumbo frames".

It's convention to call anything from 1501 to 9216 as "jumbo" and anything up to 64k "superjumbo".

View on HN

> There is no standard.

There are standards, they just aren't relevant. 802.11(n) specifies 7935 bytes (A-MSDU), 802.3(as) specifies "frame envelope" at 2000 bytes. (The latter is to have room for encapsulation headers to be able to deliver 1500 regardless of encap.)

802.11 isn't Ethernet (though does have a larger frame size) and A-MSDU in particular standardizes aggregation of multiple MAC frames not an extension of the MAC frame. However larger frame envelopes are definitely a standardized thing for Ethernet but the IEEE folks will fight to the death it's a separate concept as you say.

Oh, yeah, don't get me started... It is SO damn freaking annoyinggly hard to set up a common packet size for all my devices! Completely ridiculous! For example, I have NAS-to-Switch 10G fiber that supports > 9000, switch-to-clients 10G fiber and 1G copper, and every damn machine has different NIC with not only different frame caps (some 4K, some 8K, some 9K, others unknown), but they represent different numbers!! For example, Intel vs Mellanox accept byte numbers with and without headers (don't remember which is which) - try guessing! That's in Windows, of course. Where vendors design their UIs/configs.

Also, these problems are hard to debug. Oh, and don't ask me what happens if someone crams in a small dumb noname switch in the net...

Huh where can I read more about super jumbo, I could use it.

Start with your NIC driver. Most I've seen don't support frame sizes over 9000ish, which I assume reflects a hardware limitation.

Reply on news.ycombinator.com