Understanding How Port Negotiation Works - Cisco WS-C2948G-GE-TX Configuration Manual

Chapter 5 Configuring Gigabit Ethernet Switching
Table 5-2
Configuration
receive off
receive
desired

Understanding How Port Negotiation Works

Caution Unlike autonegotiation with 10/100 Fast Ethernet, Gigabit Ethernet port negotiation does not involve
negotiating port speed. You cannot disable port negotiation on Gigabit Ethernet ports using the set port
speed command.
Note Port negotiation is not supported on 1000BASE-T Gigabit Ethernet ports.
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.
Note On 1000BASE-T Gigabit Ethernet ports, you cannot configure speed or duplex mode. With this release,
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.
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
78-15908-01
Send and Receive Keyword Configurations (continued)
Description
Prevents a local port from processing pause frames. Enter receive off when a remote
port is set to send off or send desired.
Indicates preference to process pause frames, but autonegotiates flow control. You
can enter receive desired when a remote port is set to send on, send off, or send
desired.
Table 5-3 shows the four possible port negotiation configurations for a Gigabit
Gigabit Ethernet Port Negotiation Configuration and Possible Link States
1 2
Far End
Off
On
On
Off
Understanding How Gigabit Ethernet Works
Link Status
Near End Far End
Up Up
Up Up
Up Down
Down Up
5-3