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Understanding How Gigabit Ethernet Works
Oversubscribed Gigabit Ethernet Overview
The Catalyst 4000 family Gigabit Ethernet modules provide a network-backbone connection for multiple
servers or high-end workstations. The following modules are supported:
•
•
On all modules, each uplink module port has 1-Gbps dedicated bandwidth. These ports typically connect
to the network backbone.
Table 5-4
Table 5-4
Module
WS-X4412-2GB-T
WS-X4418-GB
On all modules, the oversubscribed ports are segmented into groups of four ports each. Each group of
four ports shares 1 Gbps of bandwidth. The average bandwidth that clients and servers need to connect
to ports in the same group should not exceed 1 Gbps.
Table 5-5
Table 5-5
1
Table 5-6
Table 5-6
Uplink Ports
1
The oversubscribed Gigabit Ethernet ports are designed for end-station connections. We do not
recommend connecting these ports to switches or routers.
Each group of four oversubscribed ports has a buffer for incoming frames to allow connected devices to
transmit traffic simultaneously. Because the inbound buffer is small, the default (and recommended)
flow-control configuration for the oversubscribed ports is receive desired and transmit on.
You can bundle multiple oversubscribed ports into a Gigabit EtherChannel link to connect to
channel-capable servers. Bundling multiple oversubscribed ports in the same port group increases the
total available bandwidth and provides redundancy with quick failover for links to servers and hosts that
support the Port Aggregation Protocol (PAgP).
Software Configuration Guide—Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4
5-4
WS-X4412-2GB-T
This 1000BASE-T 14-port module provides 2 dedicated uplink module ports (GBIC) and
12 oversubscribed ports (possible blocking).
WS-X4418-GB
This 1000BASE-X 18-port module provides 2 dedicated uplink module ports (GBIC) and
16 oversubscribed ports (possible blocking).
lists the uplink module port IDs for each module.
Uplink Port Module IDs for Gigabit Ethernet Modules
shows how the oversubscribed ports are grouped for module WS-4412-2GB-TX.
Oversubscribed Port Groupings for Module WS-4412-2GB-TX
2
3
4
5
6
shows how the oversubscribed ports are grouped for module WS-4418-2GB.
Oversubscribed Port Groupings for Module WS-4418-2GB
2
Port ID
13 14
1 2
7
8
9
10
11
3
5
7
9
4 6
8 10
Chapter 5
Configuring Gigabit Ethernet Switching
Uplink Ports
12
13
14
11
13
15
17
12 14
16 18
78-12647-02
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Troubleshooting
