Autonegotiation & MDIX

100BASE-TX: Autonegotiation is optional, duplex and speed can be forced or auto. Auto MDIX is required when using a strait through cable between two MDI ports or two MDIX ports. With a cross over it is optional

1000BASE-T: Autonegotiation is mandatory required, auto speed and duplex required when using autonegotiation. Autonegotiation is requird for choosing master/slave timings between two connected interfaces. It is also required to connect a GigE port to a 100Base-TX for example, for backward compatability. From the Wikipedia page: "Autonegotiation is a requirement for using 1000BASE-T according to Section 28D.5 Extensions required for Clause40 (1000BASE-T). At least the clock source has to be negotiated, as one endpoint must be master and the other endpoint must be slave."

1000BASE-X: Autonegotiation is optional, duplex can be foreced or auto to match (auto is recommended). Speed maybe auto or fixed but can only bee 1000Mbps.

10GBASE-T: Autonegotiation is optional.

10GBASE-X: Autonegotiation is mandatory disabled. Speed is normally detected by the speed of the PHY (inserting a 10G SFP for example).

100GBASE-LR4: Autonegotiation is not supported.

 

References:

http://www.ieee802.org/3/hssg/public/sep06/law_01_0906.pdf

http://standards.ieee.org/reading/ieee/interp/IEEE802.3af-2003interp-6.pdf

https://www.iol.unh.edu/services/testing/ge/knowledgebase/Clause_37_Auto-Negotiation.pdf

http://en.wikipedia.org/wiki/Autonegotiation

http://en.wikipedia.org/wiki/Medium_Dependent_Interface

https://en.wikipedia.org/wiki/100_gigabit_Ethernet#Coding_schemes

 

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