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This chapter describes how to configure Ethernet and Fast Ethernet switching on the Catalyst 5000, 4000, 2948G, 2926G, and 2926 series switches. The configuration tasks in this chapter apply to Ethernet and Fast Ethernet switch ports on switching modules and fixed-configuration switches, as well as to supervisor engine Fast Ethernet uplink ports.
This chapter consists of these sections:
These sections describe how Ethernet switching works on the Catalyst 5000, 4000, 2948G, 2926G, and 2926 series switches:
The Catalyst 5000, 4000, 2948G, 2926G, and 2926 series switches support simultaneous, parallel conversations between Ethernet segments. Switched connections between Ethernet segments last only for the duration of the packet. New connections can be made between different segments for the next packet.
The Catalyst 5000, 4000, 2948G, 2926G, and 2926 series switches solve congestion problems caused by high bandwidth devices and a large number of users by assigning each device (for example, a server) to its own 10-, 100-, or 1000-Mbps segment. Because each Ethernet port on the switch represents a separate Ethernet segment, servers in a properly configured switched environment achieve full access to the bandwidth.
Because the major bottleneck in Ethernet networks is usually due to collisions, an effective solution is full-duplex communication, an option for each port on the switches (Gigabit Ethernet ports only support full duplex). Normally, Ethernet operates in half-duplex mode, which means that stations can either receive or transmit. In full-duplex mode, two stations can transmit and receive at the same time. When packets can flow in both directions simultaneously, effective Ethernet bandwidth for Ethernet ports is 20 Mbps, for Fast Ethernet ports 200 Mbps, and for Gigabit Ethernet ports 2 Gbps.
Each Ethernet port on the switch can connect to a single workstation or server, or to a hub through which workstations or servers connect to the network.
Ports on a typical Ethernet hub all connect to a common backplane within the hub, and the bandwidth of the network is shared by all devices attached to the hub. If two stations establish a session that uses a significant level of bandwidth, the network performance of all other stations attached to the hub is degraded.
To reduce degradation, the Catalyst 5000, 4000, 2948G, 2926G, and 2926 series switches treat each port as an individual segment. When stations on different ports need to communicate, the switch forwards frames from one port to the other at wire speed to ensure that each session receives the full bandwidth available.
To switch frames between ports efficiently, the switch maintains an address table. When a frame enters the switch, it associates the Media Access Control (MAC) address of the sending station with the port on which it was received.
The switch builds the address table by using the source address of the frames received. When the switch receives a frame for a destination address not yet listed in its address table, it floods the frame to all ports of the same virtual LAN (VLAN) except the port that received the frame. When the destination station replies, the switch adds its relevant source address and port ID to the address table. The switch then forwards subsequent frames to a single port without flooding to all ports.
The address table can store at least 16,000 address entries without flooding any entries. The switch uses an aging mechanism, defined by a configurable aging timer, so if an address remains inactive for a specified number of seconds, it is removed from the address table.
Table 4-1 shows the Ethernet and Fast Ethernet default configuration.
| Feature | Default Value |
|---|---|
Port enable state | All ports are enabled |
Port name | None |
Port priority | Normal |
Duplex mode |
|
Spanning-Tree Protocol | Enabled for VLAN 1 |
Native VLAN | VLAN 1 |
Port VLAN cost |
|
Fast EtherChannel | Disabled on all Fast Ethernet ports (auto mode) |
These sections describe how to configure Ethernet and Fast Ethernet switching ports on the Catalyst 5000, 4000, 2948G, 2926G, and 2926 series switches:
You can assign names to the ports on Ethernet and Fast Ethernet modules to facilitate switch administration.
To assign a name to a port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Assign a name to a port. | set port name mod_num/port_num [name_string] |
Step 2 Verify that the port name is configured. | show port [mod_num[/port_num]] |
This example shows how to set the name for ports 1/1 and 1/2 and how to verify that the port names are configured correctly:
Console> (enable) set port name 1/1 Router Connection Port 1/1 name set. Console> (enable) set port name 1/2 Server Link Port 1/2 name set. Console> (enable) show port 1 Port Name Status Vlan Level Duplex Speed Type ----- ------------------ ---------- ---------- ------ ------ ----- ------------ 1/1 Router Connection connected trunk normal half 100 100BaseTX 1/2 Server Link connected trunk normal half 100 100BaseTX <...output truncated...> Last-Time-Cleared -------------------------- Tue Jun 16 1998, 16:25:57 Console> (enable)
You can configure the priority level of each port. When ports request access to the switching bus simultaneously, the switch uses the port priority level to determine the order in which ports are given access.
To set the port priority level, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Configure the priority level for a port. | set port level mod_num/port_num {normal | high} |
Step 2 Verify that the port priority level is configured correctly. | show port [mod_num[/port_num]] |
This example shows how to set the port priority level to high for port 1/1 and verify that the port priority is configured correctly:
Console> (enable) set port level 1/1 high Port 1/1 level set to high. Console> (enable) show port 1 Port Name Status Vlan Level Duplex Speed Type ----- ------------------ ---------- ---------- ------ ------ ----- ------------ 1/1 Router Connection connected trunk high half 100 100BaseTX 1/2 Server Link connected trunk normal half 100 100BaseTX <...output truncated...> Last-Time-Cleared -------------------------- Tue Jun 16 1998, 16:25:57 Console> (enable)
You can configure the port speed on 10/100-Mbps Fast Ethernet modules. Use the auto keyword to have the port autonegotiate speed and duplex mode with the neighboring port.
 | Caution Make sure the device on the other end of the link is also configured for autonegotiation or a port speed or duplex mismatch will result. |
To set the port speed for a 10/100-Mbps port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Set the port speed of a 10/100-Mbps Fast Ethernet port. | set port speed mod num/port num {10 | 100 | auto} |
Step 2 Verify that the speed of the port is configured correctly. | show port [mod_num[/port_num]] |
This example shows how to set the port speed to 100 Mbps on port 2/2:
Console> (enable) set port speed 2/2 100 Port 2/2 speed set to 100 Mbps. Console> (enable)
This example shows how to make port 2/1 autonegotiate speed and duplex with the neighbor port:
Console> (enable) set port speed 2/1 auto Port 2/1 speed set to auto-sensing mode. Console> (enable)
You can set the port duplex mode to full or half duplex for Ethernet and Fast Ethernet ports.
To set the duplex mode of a port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Set the duplex mode of a port. | set port duplex mod num/port num {full | half} |
Step 2 Verify that the duplex mode of the port is configured correctly. | show port [mod_num[/port_num]] |
This example shows how to set the duplex mode to half duplex on port 2/1:
Console> (enable) set port duplex 2/1 half Port 2/1 set to half-duplex. Console> (enable)
Use the ping and traceroute commands to test connectivity out Ethernet or Fast Ethernet ports.
To check connectivity out a port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Ping a remote host that is located out the port you want to test. | ping [-s] host [packet_size] [packet_count] |
Step 2 Trace the hop-by-hop route of packets from the switch to a remote host located out the port you want to test. | traceroute host |
Step 3 If the host is unresponsive, check the IP address and default gateway configured on the switch. | show interface |
This example shows how to ping a remote host and how to trace the hop-by-hop path of packets through the network using traceroute:
Console> (enable) ping somehost somehost is alive Console> (enable) traceroute somehost traceroute to somehost.company.com (10.1.2.3), 30 hops max, 40 byte packets 1 engineering-1.company.com (173.31.192.206) 2 ms 1 ms 1 ms 2 engineering-2.company.com (173.31.196.204) 2 ms 3 ms 2 ms 3 gateway_a.company.com (173.16.1.201) 6 ms 3 ms 3 ms 4 somehost.company.com (10.1.2.3) 3 ms * 2 ms Console> (enable)
Posted: Tue Mar 30 15:56:37 PST 1999
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