A very long time ago (mid-November 98), when I got my F720 filer
with Gigabit ether, I tried to connect it to an Extreme Summit48,
had trouble, contacted NetApp, despite excellent suggestions still
had trouble and appealed to this list.  Got a few "let us know what
happens", but unfortunately no real leads.
The story has a happy ending, and here's what did happen.
First off: Gigabit on F720 to Summit48 works great.  That's settled.
Also, with the help I got from NetApp (Mark Smith, Tim McCarthy,
David Zwick, Devi Nagaraj, possibly others!), if I had been actually
able to concentrate on the problem for more than 30 minutes at a
time (and more than 60 minutes per week :-), I might have noticed
what was going on earlier.
What the problem turned out to be is: on both of the Summit48's I
had available to me to test the Gig ether link, the port I was
using, always port 50, was missing from any VLAN list.  What *that*
means is that although the port appeared alive, no packets were
ever delivered to that port from any other and it quietly acted as
a packet sync for anything received from the filer.
Now how did port 50 end up off of all VLANs, on both switches?
Simple!
Right after I first received my brand new switches, I had trunked
the two fiber links on the two Summit48's together, just to see if
it would work.  I ran fiber from port 49 on one to port 49 on the
other and 50 to 50.  When the F720 arrived, I moved one fiber link
(port 50) from the second Summit48 over to the 720 and unconfigured
the trunking.
But what happens when you unconfigure a trunked port on a Summit,
apparently, is that the port ends up not being on *any* VLAN.  The
port is "alive" but nothing is routed to or from it.
So, I reconfigured the affected ports (put all ports back on the
Default VLAN) and the G/B link to the 720 now works just fine.
There's still one small "cosmetic" glitch.  When the filer comes
up, it always reports that the G/B link is up, then right away that
it's down.  The last console message is always "e8: link down".
But it is up (or I couldn't type this mail), so I'm not overly
concerned.
Do I really need Gigabit ether to an F720?  Possibly not.  I've
only managed to drive the link to 1.5 times the speed of a 100Mbit
link so far.  But with the prices of Summit48's back when I bought
them, I figure the Gig interfaces came for free.  Plus, this way I
don't have to trunk 100Mbit ether ports and waste good sockets on the
switch.
And anyway, I'm always adding more clients to load down the filer.
That reminds me: has the Progress db been certified yet?
-- 
-bmw   | Double helix in the sky tonight
       | Throw out the hardware
       | Let's do it right   -- Steely Dan; Aja