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, 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 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.