== Jumbo frames on gigabit Ethernet on Solaris 10 x86

We've recently been looking into using jumbo frames on gigabit Ethernet
on Solaris 10U4 x86 (aka Solaris 10 8/07); it turns out that this
is more work than you might expect, and information on it is somewhat
scattered.

First, as of S10U4 only a few gigabit network drivers are documented as
supporting jumbo frames:

|_. driver	| maximum MTU	|	chipset
| _bge_		| 9000	| 	Broadcom, *but only on some chipsets*;
			the manual says BCM5700, 5701,
			5702, 5703C, 5703S, 5704C, 5704S, 5714C, 5714S,
			5715C and 5715S.
| _e1000g_	| 16218	|	Intel PRO/1000
| _rge_		| ~~7000~~	|	Realtek (RTL8169S/8110S)
| _sk98sol_	| 9000	|	SysKonnect SK-98xx

(The _xge_ 10 gigabyte Ethernet driver also supports them with a
9600 byte MTU, but 10G Ethernet is far too rich for our blood right
now.  The _nxge_ driver for various Sun cards [[apparently supports
jumbo frames
http://napobo3.blogspot.com/2007/09/enabling-jumbo-frames-for-sun-x8-quad.html]],
but this is not documented in its manpage.)

Unlike what you might expect, the drivers do not automatically allow
jumbo frames. Instead you have to specifically enable them before you
can raise the MTU with _ifconfig_, and for more fun each driver does
this differently and hides their configuration files in different
places. For the ones I have personal experience with:

* _bge_ is configured in _/platform/i86pc/kernel/drv/bge.conf_
* _e100g_ is configured in _/kernel/drv/e100g.conf_

(The necessary configuration parameter is documented in each driver's
manpage.)

I don't know about jumbo frame support on S10U3, because I [[no longer
have CorruptingMetadb]] a S10U3 system handy to check its manpages.

The quite nice SunFire X2100 M2 theoretically has two jumbo-capable
_bge_ interfaces (along with two not-jumbo-capable _nge_ ones), but
one of them is the ELOM interface and you probably want that to be
on a special management network, so effectively you only get one
jumbo-capable one.