Autonegotiation FaEth work ?

Unanswered Question
Jun 29th, 2007

SW PC

Auto Auto------->?

100/Full Auto---------->100/half

Auto 100/Full----->100/half

100/Full 100/Full---->BEST

Can any tell what does auto/auto on both sides negotiate to...?

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
mohammedmahmoud Fri, 06/29/2007 - 04:07

Hi,

When auto-negotiation is configured the speed is negotiated to the highest speed using the Fast Link Pulses (FLP), and the duplex is also negotiated (full duplex if both supports full duplex, other wise half duplex), however, if auto-negotiation is disabled on either end of the cable, the switch detects the speed anyway based on the incoming electrical signal, but the devices without a configured/negotiated duplex setting must assume a default. Cisco switches use a default duplex setting of half duplex (HDX) (for 10-Mbps and 100-Mbps interfaces) or full duplex (FDX) (for 1000-Mbps interfaces), which can introduced duplex mismatch, example if one side is auto and the other is full, the auto side will assume half duplex, which introduces duplex mismatch.

Accordingly as a best practice, either to make both sides Auto (highest matching speed on both sides, and full duplex if both supports full duplex, other wise half duplex), or configure both sides explicitly to avoid any Duplex mismatch problems.

HTH,

Mohammed Mahmoud.

guruprasadr Fri, 06/29/2007 - 04:26

HI, [PLS Rate if HELPS]

1. NIC = AUTO [ 1000 Mbps, Full-duplex ]

Switch = AUTO [ 1000 Mbps, Full-duplex ]

Comments:Assuming maximum capability of Catalyst switch, and NIC is 1000 Mbps, full-duplex.

2. NIC = 1000 Mbps, Full-duplex [ 1000 Mbps, Full-duplex ]

Switch = Auto [ 1000 Mbps, Full-duplex ]

Comments:Link is established, but the switch does not see any autonegotiation information from NIC. Since Catalyst switches support only full-duplex operation with 1000 Mbps, they default to full-duplex, and this happens only when operating at 1000 Mbps.

3. NIC = 100 / 1000 Mbps, Full-duplex

Switch = 100 / 1000 Mbps, Full-duplex

Correct Manual Configuration

4. NIC = 100 Mbps, Full-duplex [No Link]

Switch = 1000 Mbps, Full-duplex [No Link]

Comment:Neither side establishes link, due to speed mismatch

5.NIC = 100 Mbps, Full-duplex [100 Mbps, Full-duplex]

Switch = Auto [100 Mbps, Full-duplex]

Comments:Duplex Mismatch 1 & Viceversa

6. NIC = 100 Mbps, Half-duplex [100 Mbps, Half-duplex ]

Switch = Auto [100 Mbps, Half-duplex ]

Comments:Link is established, but switch does not see any autonegotiation information from NIC and defaults to half-duplex when operating at 10/100 Mbps

7. NIC = 10 Mbps, Half-duplex [10Mbps, Half-duplex ]

Switch = Auto [10Mbps, Half-duplex ]

Comments:Link is established, but switch does not see Fast Link Pulse (FLP) and defaults to 10 Mbps half-duplex.

8. NIC = 10 Mbps, Half-duplex[ No Link ]

Switch = 100 Mbps, Half-duplex [No Link]

Comments:Neither side establishes link, due to speed mismatch.

9. NIC = AUTO [100 Mbps, Half-duplex ]

Switch = 100 Mbps, Half-duplex [100 Mbps, Half-duplex ]

Comments:Link is established, but NIC does not see any autonegotiation information and defaults to 100 Mbps, half-duplex.

10.NIC = Auto [10 Mbps, Half-duplex ]

Switch = 10 Mbps, Half-duplex [10 Mbps, Half-duplex ]

Comments:Link is established, but NIC does not see FLP and defaults to 10 Mbps, half-duplex.

NOTE:NIC= [....] = Resulting NIC Speed/duplex

Switch = [....] = Resulting Switch Speed/Duplex

I hope my reply has all possible combinations for Speed / Duplex Settings with Resulting Outputs. Hope this Helps you.

PLS RATE / VOTE if HELPS

Best Regards,

Guru Prasad R

Actions

This Discussion