After a warm reboot yesterday, my server de card:

de0 at pci0 dev 11 function 0 at irq 12
de0: 21140A [10-100Mb/s] pass 2.0
de0: address 00:80:48:e9:0a:75

... got stuck with a status of "no carrier".  Its current state is:

de0: flags=8863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST> mtu
1500
        media: 100baseTX <full-duplex> status: active
        inet 10.0.0.2 netmask 0xffffff00 broadcast 10.0.0.255

Now, in this state, the two machines on either side of the link
encountered many many receive errors, mostly CRC, sometimes
alignment.  As I was upgrading the client machine's (X terminal)
kernel to 1.3_ALPHA I immediately blamed that for the newfound errors,
but it appears not to be the case.  The server kernel is 1.2G.  On a
hard reset of the server the interface came right.

I did try downing and upping the interface with no positive effect.

How to repeat, I don't know....  I can't recall having this problem
any other time I have warm booted.  I assume the card got into a state
from which the driver could not completely reset.  It's possible also
that this is fixed in 1.3 already, as the kernel in question is older.

I have no more useful information to provide.  I have a vague hope
that someone with a strong understanding of the driver (Matt?) will
click onto what caused this instantly. :)

Its not causing a real problem given the workaround of hard reseting.
It is possible a warm boot would have been enough, I just happened to
try a hard reset first.

Cheers,

Dave.