Understanding How Port Negotiation Works; Understanding How Oversubscribed Gigabit Ethernet Works - Cisco WS-C2950SX-48-SI Configuration Manual

Chapter 5 Configuring Gigabit Ethernet Switching

Understanding How Port Negotiation Works

Unlike autonegotiation with 10/100 Fast Ethernet, Gigabit Ethernet port negotiation does not involve
Caution
negotiating port speed. You cannot disable port negotiation on Gigabit Ethernet ports using the set port
speed command.
Port negotiation is not supported on 1000BASE-T Gigabit Ethernet ports.
Note
With Gigabit Ethernet ports, port negotiation is used to exchange flow-control parameters, remote fault
information, and duplex information (even though Cisco Gigabit Ethernet ports only support full-duplex
mode). With Gigabit Ethernet ports, you configure port negotiation using the set port negotiation
command. Gigabit Ethernet port negotiation is enabled by default.
The ports on both ends of a Gigabit Ethernet link must have the same setting. The link will not come up
if the ports at each end of the link are set inconsistently (port negotiation enabled on one port and
disabled on the other).
Ethernet link and the resulting link status for each configuration.
Table 5-3
Port Negotiation State
Near End
Off
On
Off
On
1. Near End refers to the local Gigabit EtherChannel module port.
2. Far End refers to the remote port at the other end of the Gigabit link.
On 1000BASE-T Gigabit Ethernet ports, you cannot configure speed or duplex mode. With this release,
Note
1000BASE-T ports operate only in the default configuration where the speed is 1000 and duplex mode
is full. You cannot disable autonegotiation at this time. On a 1000BASE-T port, you can configure flow
control and enable or disable a port. To determine which features a 1000BASE-T Gigabit Ethernet port
supports, enter the show port capabilities command.

Understanding How Oversubscribed Gigabit Ethernet Works

The Catalyst 4500 series Gigabit Ethernet modules provide a network-backbone connection for multiple
servers or high-end workstations. The following modules are supported:
•
78-15486-01
Table 5-3
Gigabit Ethernet Port Negotiation Configuration and Possible Link States
1
Far End
Off
On
On
Off
WS-X4412-2GB-T
This 1000BASE-T 14-port module provides 2 dedicated uplink module ports (GBIC) and
12 oversubscribed ports (possible blocking).
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
shows the four possible port negotiation configurations for a Gigabit
Link Status
2
Near End
Up
Up
Up
Down
Understanding How Gigabit Ethernet Works
Far End
Up
Up
Down
Up
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Release 8.1
5-3