Autonegotiation – Connecting Disabled FE Port to Enabled 10/100/1G Port

autonegotiationethernetieee-802.3xlayer1

I was just learning about auto-negotiation and got some doubts.

As per the standard 802.3 clause 28, 10BASE-T ports transmits LIT or NLP pulses to make the link UP.

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

Also when 10/100/1G (Auto-neg enabled) port is connected to 10M FD (auto-neg disabled) port, FLP from Auto-neg port and NLP from Auto-neg disable port will be transmitted, result is 10M HD and 10M FD respectively.

  1. What will happen when 10/100/1G (Auto-neg enabled) port is connected to 100M FD (auto-neg disabled) port ?
  2. Does 100M port use the same LIT/NLP ?
  3. What signaling method does 100M port use when 2 FE ports (Autoneg disabled) are connected to each other ?

Thanks in advance for reading

Best Answer

  1. Usually the port comes up - due to lack of autonegotiation, the auto side will choose half duplex, resulting in a duplex mismatch.

  2. Fast Ethernet uses "fast link pulses", an expanded scheme.

  3. Autoneg disabled on both sides leaves only the carrier (pause symbols) to detect the link. FDX/HDX will be as set up, potentially mismatching.

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