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Performance issues occur due to SPAN or RSPAN configuration in a Catalyst 6500 running CatOS system software



When the total amount of traffic aggregated from the source ports exceeds the physical limitations of the destination port, it results in some dropped packets on the destination port. This does not cause any switch performance degregation or disruption or traffic flow on the source ports. The only affected port is the destination port, and it drops packets on a First In-First Out (FIFO) basis once the egress buffer limit is exceeded.

Whenever you create SPAN sessions with many ports for sources, there is a performance impact as now the switch carries twice as much traffic.  Each linecard replicates the traffic at ingress, whenever you SPAN a port all ingress traffic is doubled when it hits the fabric.  If you capture traffic from a lot of busy ports on a linecard, it can fill up the fabric connection, for example, the 6548 linecards which has 8 gigabit fabric connection.

Refer to the Performance Impact of SPAN on the Different Catalyst Platforms section of Catalyst Switched Port Analyzer (SPAN) Configuration Example for more information.

Refer to these sections of Configuring SPAN and RSPAN for more information on Switched Port Analyzer (SPAN) or Remote SPAN (RSPAN) limitations: