[c-nsp] 3508 / GBIC ZX / Minimum IOS

[Daniel Suchy]

On 01/09/2007 08:48 AM, Gert Doering wrote:
> You might need to play with port negotiation - I've never understood what
> autonegotiation is *good* for on GigE fiber ports ("single possible speed,
> always full duplex") but if one side is set to negotiate, and the other
> side to *not* do it, you won't get a link.  BTDT.

Autonegotiation is useful for fault detection.
With negotiation disabled port becomes on device up always when signal 
is detected on laser receive port, and this can be cause of 
unidirectional links - dangerous in case of fiber cuts, for example.
With negotiation enabled is tested bidirectional communication between 
devices _before_ link comes up and also link comes on both sides down 
promptly after disconnection of any (tx,rx) fibre.

Generally isn't good idea disable autonegotiation when both devices can 
run with autonegotiation enabled, this can end in unnecessarily problems 
(for example if you're forming more interfaces in etherchannel and lose 
signal only on one of many fibers).

Dan