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| 9.1 |  | Monitoring Switched Network Performance with SPAN and VSPAN |
| 9.1.1 |  | Monitoring switched network performance with SPAN and VSPAN |

SPAN is a method of monitoring network traffic by copying source port or VLAN specific traffic to a destination port for analysis.

SPAN can be used to monitor all network traffic, including:

- Multicast and bridge protocol data unit (BPDU) frames
- Cisco Discovery Protocol (CDP) frames
- VLAN Trunk Protocol (VTP) frames
- Dynamic Trunking Protocol (DTP) frames
- Spanning-Tree Protocol (STP) frames
- Port Aggregation Protocol (PagP) frames

In some SPAN configurations, multiple copies of the same source packet are sent to the SPAN destination port. For example, a bidirectional SPAN session is configured for sources a1 and a2 to a destination port d1. A bidirectional SPAN session monitors both incoming and outgoing traffic for a port. If a packet enters the switch through a1 and gets switched to a2, both incoming and outgoing packets are sent to destination port d1. In this case, both packets would be the same. However, if the data is re-encapsulated at Layer 3, the frames will be different.