Connect & Configure Cisco Networking Devices: Part 2

Table of Contents

1. Main Menu
2. Part 2: Basic Switch Operation and Configuration
3. 2.1: LAN Switching
4. LAN Switching Continued
5. 2.2: Basic Configuration Commands
6. 2.2.1: Privilege Exec Mode Commands
7. 2.2.1: Global Configuration Mode Commands
8. 2.2.3: Line Mode Commands
9. 2.3: Displaying the contents of the MAC Address Table
10. 2.4: Switch Interfaces
11. Switch Interface Configuration Continued
12. 2.5: Assigning an IP Address & Default Gateway to a 2950 Switch
13. 2.6: Configuring Port Security
14. Video: Basic Switch and Port Security Configuration
15. 2.7: The Spanning Tree Protocol (STP)
16. 2.7.2: STP Port States
17. 2.7.3: STP Configuration
18. Review Questions for Part 2

LAN Switching Continued

Another way of describing a Switch is that it has "A Bridge per Port".

• LAN switches are essentially fast multi-port bridges:

• Protocol independent with filtering.

• Divide LAN's into smaller independent segments and interconnects those segments at full network speed.

• Low propagation delays

• LAN Switches use existing installed cabling and NIC cards

• Flexible mix of speeds

• Supports low latency applications such as video

• Provide dedicated bandwidth to each port

• LAN Switching multiplies the effective bandwidth of the network

2.1.1: Switch Frame Forwarding

There are three main types of frame forwarding with Cisco Switches:

• Cut Through - The destination MAC address is checked as soon as the frame header arrives and the frame begins to be forwarded immediately.

• Store and Forward - The complete frame is received before forwarding occurs. The Source and destination MAC address is read, and the CRC is checked. If there are no errors, the frame is forwarded otherwise it is discarded.

• Fragment Free - The first 64 bytes are read, before forwarding the frame, based on the fact that collisions happen within the first 64 bytes.

2.1.2: Full and Half Duplex

With Switches, the ports can be configured for Half Duplex or Full Duplex transmission.

Half duplex permits traffic in one direction at a time, whereas full duplex allows traffic in both directions simultaneously. Full Duplex, effectively doubles the bandwidth and prevents collisions on a port.

Full duplex can only be used on Point-to-Point connections between directly connected Switches. It is not available on ports connected to hubs.

When set for auto negotiation, a port senses the speed and duplex settings of the attached device and advertises its own capabilities. If the attached device supports auto negotiation, the port negotiates the best connection (this is the fastest line speed that both devices support and full-duplex transmission, if the attached device supports it) and configures itself accordingly

The ability to auto negotiate duplex mode depends on the device attached to a port. If one device is configured to use half duplex, problems will occur with collisions at the Full Duplex Port, resulting in the port being blocked.