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This chapter describes how to configure Ethernet and Fast Ethernet switching on the Catalyst 5000, 4000, 2948G, and 2926G 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, and 2926G series switches:
The Catalyst 5000, 4000, 2948G, and 2926G 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, and 2926G 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, and 2926G 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.
Certain Fast Ethernet ports can transmit flow-control frames (pause frames) and can respond to pause frames received from neighboring devices. When a pause frame is received on a port, it is processed internally; pause frames are not switched through the system. Fast Ethernet ports that support flow control include:
If the receive buffer for a switch port becomes full, the switch transmits a pause packet on that port that tells neighboring devices to delay sending more packets for a specified period of time. Similarly, the switch can respond to pause frames received from a neighboring device by inhibiting the transmission of packets from a port for a period of time.
Use the set port flow control command to configure flow control on Fast Ethernet ports. Table 4-1 describes the flow-control behavior of a Fast Ethernet port depending on the set port flowcontrol command keywords used to configure the port.
| Keywords | Port Behavior |
|---|---|
receive on | The port uses flow control dictated by the neighbor port. |
receive desired | The port uses flow control if the neighbor port uses it, and does not use flow control if the neighbor port does not use it. |
receive off | The port does not use flow control, regardless of whether flow control is requested by the neighbor port. |
send on | The port sends flow-control frames to the neighbor port. |
send desired | The port sends flow-control frames to the neighbor port if the neighbor port asks to use flow control. |
send off | The port does not send flow-control frames to the neighbor port. |
Certain 10/100-Mbps and 100-Mbps Fast Ethernet ports support link negotiation. Link negotiation is used to exchange flow-control parameters, remote fault information, and duplex information. With Gigabit Ethernet ports, you configure link negotiation using the set port negotiation command. Gigabit Ethernet port negotiation is enabled by default.
 | Caution Unlike Fast Ethernet autonegotiation, Fast Ethernet link negotiation does not involve negotiating port speed. You cannot disable link negotiation on Fast Ethernet ports using the set port speed command. |
The ports on both ends of a Fast Ethernet link must have the same link negotiation setting. The link will not come up if the ports at each end of the link are set inconsistently (link negotiation enabled on one port and disabled on the other). Table 4-2 shows the four possible link negotiation configurations for a Fast Ethernet link and the resulting link status for each configuration.
| Link Negotiation State | Link Status | ||
| Near End1 | Far End2 | Near End | Far End |
Off | Off | Up | Up |
On | On | Up | Up |
Off | On | Up | Down |
On | Off | Down | Up |
| 1Near End refers to the local Fast Ethernet module port. 2Far End refers to the remote port at the other end of the Fast Ethernet link. |
Table 4-3 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 |
|
Flow control (on supported modules only) | Flow control set to off for receive (Rx) and on for transmit (Tx) |
Link negotiation (on supported modules only) | Enabled |
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, and 2926G 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)
To configure flow control on a Fast Ethernet port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Set the flow-control parameters on a Fast Ethernet port. | set port flowcontrol {receive | send} mod_num/port_num {off | on | desired} |
Step 2 Verify the flow-control configuration. | show port flowcontrol |
This example shows how to turn transmit and receive flow control on and how to verify the flow-control configuration:
Console> (enable) set port flowcontrol 4/1 send on
Port 4/1 flow control send administration status set to on
(port will send flowcontrol to far end)
Console> (enable) set port flowcontrol 4/1 receive on
Port 4/1 flow control receive administration status set to on
(port will require far end to send flowcontrol)
Console> (enable) show port flowcontrol 4/1
Port Send FlowControl Receive FlowControl RxPause TxPause Unsupported
admin oper admin oper opcodes
----- -------- -------- -------- -------- ------- ------- -----------
4/1 on on on on 0 0 0
Console> (enable)
To enable link negotiation on a Fast Ethernet port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Enable Fast Ethernet link negotiation. | set port negotiation mod_num/port_num enable |
Step 2 Verify the link negotiation configuration. | show port negotiation [mod_num/port_num] |
This example shows how to enable port negotiation and verify the configuration:
Console> (enable) set port negotiation 2/1 enable Port 2/1 negotiation enabled Console> (enable) show port negotiation 2/1 Port Link Negotiation ----- ---------------- 2/1 enabled Console> (enable)
To disable link negotiation on a Fast Ethernet port, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Disable Fast Ethernet link negotiation. | set port negotiation mod_num/port_num disable |
Step 2 Verify the link negotiation configuration. | show port negotiation [mod_num/port_num] |
This example shows how to disable port negotiation and verify the configuration:
Console> (enable) set port negotiation 2/1 disable Port 2/1 negotiation disabled Console> (enable) show port negotiation 2/1 Port Link Negotiation ----- ---------------- 2/1 disabled 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: Mon Jul 19 12:39:28 PDT 1999
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