NFE setting manually to 1000baseT and half duplex

Matthew Seaman m.seaman at
Sun Jun 8 10:33:18 UTC 2008

Erik Trulsson wrote:

> (IIRC a switch or NIC that is set to auto-negotiate, but where the
> negotiation fails (possibly because the other end is not set to
> auto-negotiate) will usually revert to 10Mbps/half-duplex, i.e. the
> original, slowest, Ethernet speed.)

100Mb half-duplex is the default setting in this sort of mismatch.  It
will 'sort of' work, but you'll find performance is terrible and there
will be significant amounts of packet loss.

Note too that 1Gb speeds require both sides to be set to autonegotiate
-- it's part of the standard for supporting those speeds, so that in
the event of transmission difficulties the connection can be gracefully
degraded rather than just ceasing to work at all.

There's a lot of received wisdom around that wiring down connection
speeds is a good idea.  That may have been the case 5 or more years ago,
when there were certainly some combinations of NIC / network switch
manufacturer that just wouldn't negotiate correctly, but now that 
1Gb/s capability is pretty much standard such incompatibilities are
rare.  Nowadays, for best results, auto-negotiate.



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP:     Ramsgate
                                                  Kent, CT11 9PW

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