Cisco WS-C2980G-A Software Guide - Page 67

Understanding How Port Negotiation Works, Understanding How Oversubscribed Gigabit Ethernet Works

Page 67 highlights

Chapter 5 Configuring Gigabit Ethernet Switching Understanding How Gigabit Ethernet Works 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). Table 5-3 shows the four possible port negotiation configurations for a Gigabit Ethernet link and the resulting link status for each configuration. Table 5-3 Gigabit Ethernet Port Negotiation Configuration and Possible Link States Port Negotiation State Near End1 Far End2 Link Status Near End Off Off Up On On Up Off On Up On Off Down 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. Far End Up Up Down Up 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. 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: • WS-X4412-2GB-T This 1000BASE-T 14-port module provides 2 dedicated uplink module ports (GBIC) and 12 oversubscribed ports (possible blocking). 78-15486-01 Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide-Release 8.1 5-3

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5-3
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2980G Switches Software Configuration Guide
Release 8.1
78-15486-01
Chapter 5
Configuring Gigabit Ethernet Switching
Understanding How Gigabit Ethernet Works
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).
Table 5-3
shows the four possible port negotiation configurations for a Gigabit
Ethernet link and the resulting link status for each configuration.
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.
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:
WS-X4412-2GB-T
This 1000BASE-T 14-port module provides 2 dedicated uplink module ports (GBIC) and
12 oversubscribed ports (possible blocking).
Table 5-3
Gigabit Ethernet Port Negotiation Configuration and Possible Link States
Port Negotiation State
Link Status
Near End
1
1.
Near End refers to the local Gigabit EtherChannel module port.
Far End
2
2.
Far End refers to the remote port at the other end of the Gigabit link.
Near End
Far End
Off
Off
Up
Up
On
On
Up
Up
Off
On
Up
Down
On
Off
Down
Up