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Duplicate packets are seen when VLAN-based SPAN (VSPAN) is configured on Catalyst 6500/6000 in either both, tx or rx direction

Core issue

VLAN-based SPAN (VSPAN) is used for the analysis of network traffic in one or more VLANs. You can configure VSPAN as ingress SPAN, egress SPAN, or both. For VSPAN sessions with both ingress and egress SPAN configured, the system operates as follows based upon the type of supervisor engine you have:

  • WS-X6K-SUP1A-PFC, WS-X6K-SUP1A-MSFC, WS-X6K-SUP1A-MSFC2, WS-X6K-SUP2-PFC2, WS-X6K-SUP2-MSFC2 -- Two packets are forwarded by the SPAN destination port if the packets get switched on the same VLAN.
  • WS-X6K-SUP1-2GE, WS-X6K-SUP1A-2GE -- Only one packet is forwarded by the SPAN destination port.

For VSPAN sessions with both ingress and egress configured, two packets are forwarded from the destination port if the packets get switched on the same VLAN (one as ingress traffic from the ingress port and one as egress traffic from the egress port). For VSPAN sessions with either Tx or Rx configured, the packets are re-transmitted back into the same VLAN by the internal router. In such scenarios, it is possible to see duplicate copies of a packet at the destination port.

This behavior is filed in the following bugs:

Resolution

This is a generic behavior of the SPAN feature and exists in all CatOS platforms. To further resolve this problem, open a service request with Cisco Technical Support.

Version history
Revision #:
1 of 1
Last update:
‎06-22-2009 05:12 PM
Updated by:
 
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