Re: What's "maximum packet size"?

[Jacob Nevins <jacobn+secsh%chiark.greenend.org.uk@localhost>]

der Mouse writes:
> There's a "maximum packet size" in CHANNEL_OPEN and
> CHANNEL_OPEN_CONFIRMATION messages. [...]
> Have I misinterpreted 4254?  If so, what *is* that the maximum size of?
> The only other thing that makes any sense to me is that it's the "data"
> field of CHANNEL_DATA packets (see 4254 5.2); is that what it's
> supposed to be?

I believe that this (maximum length of channel data) is the correct
interpretation. (FWIW, it's what both PuTTY and OpenSSH used, last time
I looked.)

This was discussed at least once before, in Oct-Nov 2005 (subject
'Definition of "packet"'), and that seemed to be the consensus. Language
was added to what became section 5.2 of 4254 in an attempt to clarify
this.
However, perhaps unfortunately, it still does not spell out the precise
relationship between the "maximum packet size" and the number of bytes
of channel data; it just says that "The maximum amount of data allowed
is *determined* by the maximum packet size for the channel [...]" (my
emphasis).
The relationship with the transport layer is discussed in the next
paragraphs, but again it's not entirely unambiguous.