Auto-Negotiation lets devices share a link, and automatically configures both devices so that they take maximum advantage of their abilities. Auto-Negotiation uses a modified 10BASE-T link integrity test pulse sequence to determine device ability.
Important
Product-specific considerations for Auto-Negotiation include:
If Auto-Negotiation is disabled, the following hardware does not support half-duplex:
8424GT ESM
8424XT ESM
VSP 7254XTQ
Configure Auto-Negotiation as shown in the following table, where A and B are two Ethernet devices.
|
Port on A |
Port on B |
Remarks |
Best practice |
|---|---|---|---|
|
Auto-Negotiation enabled |
Auto-Negotiation enabled |
Ports negotiate on highest supported mode on both sides. |
Use this configuration if both ports support Auto-Negotiation mode. |
|
Full-duplex |
Full-duplex |
Both sides require the same mode. |
Use this configuration if you require full-duplex, but the configuration does not support Auto-Negotiation. |
Auto-Negotiation cannot detect the identities of neighbors and cannot shut down misconnected ports. Upper-layer protocols perform these functions.
Note
10 GigabitEthernet (GbE) fiber-based I/O module ports can operate at either 1 Gigabit per second (Gbps) or 10 Gbps, depending upon the capabilities of the optical transceiver that you install.
This situation presents an ambiguity with respect to the Auto-Negotiation configuration of the port, while 1 GbE ports require Auto-Negotiation; Auto-Negotiation is not defined and is non-existent for 10 GbE ports.
For a 10-GbE fiber-based I/O module, you can swap between 1 GbE and 10 GbE operation by simply swapping transceivers. To help with the swap, you can configure Auto-Negotiation when you install a 10 GbE transceiver, even though Auto-Negotiation is not defined for 10 GbE.
You can do this in anticipation of a port changeover from 10 GbE to 1 GbE. In this manner, you can pre-configure a port in 1 GbE mode while the 10 GbE transceiver is still installed. The port is ready to go upon the changeover to the 1 GbE transceiver.
You can use a saved configuration file with Auto-Negotiation enabled, to boot a system with either 10 GbE or 1 GbE transceivers installed. If you install a 1 GbE transceiver, the system applies Auto-Negotiation. If you install a 10 GbE transceiver, the system does not remove the Auto-Negotiation settings from the configuration, but the system simply ignores the configuration because Auto-Negotiation settings are irrelevant to a 10 GbE transceiver. The system preserves the saved configuration for Auto-Negotiation when re-saved no matter which speed of transceiver you install.