From all my observations, if both ends are 100Base-LX (or BX or T) and are set to auto-negotiate then they will negotiate to full-duplex. If one end is manually configured for full duplex and the other end is configured as auto then that end _may_ end up as half-duplex.
This is particularly true when connecting a 1G port to a port configured as 100M full-duplex port. If the 1G is configured for auto-speed then it _will_ negotiate to 100M half-duplex resulting in traffic impact. HTH, Nitin ________________________________________ From: NANOG <nanog-bounces@nanog.org> on behalf of Jason Lixfeld <jason+nanog@lixfeld.ca> Sent: Monday, February 29, 2016 11:07 AM To: NANOG Subject: Duplex negotiation over 100Base fibre Hello, My understanding is that for 1G and 10G optical networks, there is no concept of half-duplex mode, but I’m unclear about half duplex in the 100M optical world. Specifically, if I connect two 100Base-LX (or BX) transceivers together, is there a requirement for the controller(s on either side) to select between full or half duplex, either by static configuration, or auto-negotiation? Thanks!