Note: This section is only applicable for 10/100/1000 Mbps (1000BASE-T) NICs, and not 1000BASE-X NICs.
Table 1—Autonegotiation Valid Configuration Table
|
Configuration NIC (Speed/Duplex) |
Configuration Switch (Speed/Duplex) |
Resulting NIC Speed/Duplex |
Resulting Catalyst Speed/Duplex |
Comments |
|---|---|---|---|---|
|
AUTO |
AUTO |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
Assuming maximum capability of Catalyst switch, and NIC is 1000 Mbps, full-duplex. |
|
1000 Mbps, Full-duplex |
AUTO |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
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. |
|
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
Correct Manual Configuration |
|
100 Mbps, Full-duplex |
1000 Mbps, Full-duplex |
No Link |
No Link |
Neither side establishes link, due to speed mismatch |
|
100 Mbps, Full-duplex |
AUTO |
100 Mbps, Full-duplex |
100 Mbps, Half-duplex |
Duplex Mismatch 1 |
|
AUTO |
100 Mbps, Full-duplex |
100 Mbps, Half-duplex |
100 Mbps, Full-duplex |
Duplex Mismatch 1 |
|
100 Mbps, Full-duplex |
100 Mbps, Full-duplex |
100 Mbps, Full-duplex |
100 Mbps, Full-duplex |
Correct Manual Configuration2 |
|
100 Mbps, Half-duplex |
AUTO |
100 Mbps, Half-duplex |
100 Mbps, Half-duplex |
Link is established, but switch does not see any autonegotiation information from NIC and defaults to half-duplex when operating at 10/100 Mbps. |
|
10 Mbps, Half-duplex |
AUTO |
10 Mbps, Half-duplex |
10 Mbps, Half-duplex |
Link is established, but switch does not see Fast Link Pulse (FLP) and defaults to 10 Mbps half-duplex. |
|
10 Mbps, Half-duplex |
100 Mbps, Half-duplex |
No Link |
No Link |
Neither side establishes link, due to speed mismatch. |
|
AUTO |
100 Mbps, Half-duplex |
100 Mbps, Half-duplex |
100 Mbps, Half-duplex |
Link is established, but NIC does not see any autonegotiation information and defaults to 100 Mbps, half-duplex. |
|
AUTO |
10 Mbps, Half-duplex |
10 Mbps, Half-duplex |
10 Mbps, Half-duplex |
Link is established, but NIC does not see FLP and defaults to 10 Mbps, half-duplex. |
1 A duplex mismatch may result in performance issues, intermittent connectivity, and loss of communication. When troubleshooting NIC issues, verify that the NIC and switch are using a valid configuration.
2 Some third-party NIC cards may fall back to half-duplex operation mode, even though both the switchport and NIC configuration have been manually configured for 100 Mbps, full-duplex. This behavior is due to the fact that NIC autonegotiation link detection is still operating when the NIC has been manually configured. This causes duplex inconsistency between the switchport and the NIC. Symptoms include poor port performance and frame check sequence (FCS) errors that increment
on the switchport. To tro
ubleshoot this issue, try manually configuring the switchport to 100 Mbps, half-duplex. If this action resolves the connectivity problems,爕ou may be running into this NIC issue. Try updating to the latest drivers for your NIC, or contact your NIC card vendor for additional support.
As indicated in the Autonegotiation Valid Configuration Table above, manually setting the speed and duplex for full-duplex on one link partner results in a duplex mismatch. This is the result of disabling autonegotiation on one link partner while the other link partner defaults to a half-duplex configuration. A duplex mismatch results in slow performance, intermittent connectivity, data link errors, and other issues. If the intent is not to use autonegotiation, both link partners must be manually configured for speed and duplex for full-duplex settings.
Recommended Port Configuration (Autonegotiation or Manual Configuration)
There are many opinions on the subject of autonegotiation. Previously, many engineers advised customers not to use autonegotiation with any switch-connected device. However, improvements in the interoperation of autonegotiation and the maturity of the technology has recently changed the view of using autonegotiation. In addition, performance issues due to duplex mismatches, caused by the manual setting of speed and duplex on only one link partner, have become more common. Because of these recent issues, the use of autonegotiation is regarded as a valid practice.
EtherChannel and Trunking Between Catalyst Switches and NICs
EtherChannel can be configured dynamically using Port Aggregation Protocol (PAgP), and trunking can also be configured dynamically using Dynamic Trunking Protocol (DTP). Both PAgP and DTP are Cisco proprietary protocols and supported only on Catalyst switches. If you want to configure EtherChannel or trunking between Catalyst switches and NICs, it is recommended that you configure these features statically, as other vendor NICs may not support PAgP and DTP. On Catalyst switches, configure the EtherChannel mode to on and trunking mode to nonegotiate, which disables the PAgP and DTP protocols. If you configure the switch port with auto or desirable mode, you may not be able to form the EtherChannel or trunk with NICs.
更多交换机与NIC之间的排错 http://www.cisco.com/warp/public/473/46.html
Why Is It That the Speed and Duplex Cannot Be Hardcoded on Only One Link Partner?
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