Source Port; Destination Port - Cisco Catalyst 2950 Software Manual

Understanding SPAN
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Source Port

A source port (also called a monitored port) is a switched port that you monitor for network traffic
analysis. In a single SPAN session, you can monitor source port traffic such as received (Rx), transmitted
(Tx), or bidirectional (both). The switch supports any number of source ports (up to the maximum
number of available ports on the switch).
A source port has these characteristics:
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You can configure a trunk port as a source port. All VLANs active on the trunk are monitored on a trunk
source port.

Destination Port

A SPAN session must have a destination port (also called a monitoring port) that receives a copy of
traffic from the source port.
The destination port has these characteristics:
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Catalyst 2950 Desktop Switch Software Configuration Guide
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Some features that can cause a packet to be dropped during transmit processing might also affect the
duplicated copy for SPAN. These features include IP standard and extended output ACLs on
multicast packets and egress QoS policing. In the case of output ACLs, if the SPAN source drops
the packet, the SPAN destination would also drop the packet. If the source port is oversubscribed,
the destination ports will have different dropping behavior.
Both—In a SPAN session, a series or range of ports can be monitored for both received and sent
packets.
It can be any port type (for example, EtherChannel, Fast Ethernet, Gigabit Ethernet, and so forth).
It cannot be a destination port.
Each source port can be configured with a direction (ingress, egress, or both) to monitor. For
EtherChannel sources, the monitored direction would apply to all the physical ports in the group.
Source ports can be in the same or different VLANs.
It must reside on the same switch as the source port.
It can be any Ethernet physical port.
It cannot be a source port.
It cannot be an EtherChannel port.
When it is active, incoming traffic is disabled; it does not forward any traffic except that required
for the SPAN session.
It does not participate in spanning tree while the SPAN session is active.
When it is an active destination port, it does not participate in any of the Layer 2 protocols (STP,
VTP, CDP, DTP, PagP).
No address learning occurs on the destination port.
Chapter 10 Configuring the Switch Ports
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