2.1.g [i] SPAN, RSPAN, ERSPAN
notable rules concerning span:
Traffic monitoring in a SPAN session has these restrictions:
•Sources can be ports or VLANs, but you cannot mix source ports and source VLANs in the same session.
•The switch supports up to two source sessions (local SPAN and RSPAN source sessions). You can run both a local SPAN and an RSPAN source session in the same switch stack. The switch stack supports a total of 66 source and RSPAN destination sessions.
•You can have multiple destination ports in a SPAN session, but no more than 64 destination ports per switch stack.
•You can configure two separate SPAN or RSPAN source sessions with separate or overlapping sets of SPAN source ports and VLANs.
•SPAN sessions do not interfere with the normal operation of the switch. However, an oversubscribed SPAN destination, for example, a 10-Mb/s port monitoring a 100-Mb/s port, can result in dropped or lost packets.
•When RSPAN is enabled, each packet being monitored is transmitted twice, once as normal traffic and once as a monitored packet. Therefore monitoring a large number of ports or VLANs could potentially generate large amounts of network traffic.
•You can configure SPAN sessions on disabled ports; however, a SPAN session does not become active unless you enable the destination port and at least one source port or VLAN for that session.
•The switch does not support a combination of local SPAN and RSPAN in a single session. That is, an RSPAN source session cannot have a local destination port, an RSPAN destination session cannot have a local source port, and an RSPAN destination session and an RSPAN source session that are using the same RSPAN VLAN cannot run on the same switch stack.