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Additional packet appear at observe-port because specific realization of mirror feature at S93

Publication Date:  2012-07-27 Views:  26 Downloads:  0
Issue Description
Customer use topo PointA - S93_A ---- MPLS link ------S93_B -----PointB.
PontA and PointB bind using VPLS service, so packet from A to B have MPLS header at MPLS link.
Customer send PADI packets from pointA to pointB. At S93_A and S93_B configured mirror feature and at neigbor interface trying capture packets. Packet capture show unexpected result:
Case 1
Capture packet at S93_A, mirror OUT direction of MPLS link.
Capture display packet without MPLS header

Case 2
Capture packet at S93_B, mirror BOTH direction of MPLS link.
Capture display packet with MPLS header and additional packet without MPLS header

Case 3
Capture packet at S93_B, mirror IN direction of MPLS link.
Capture display packet only with MPLS header, as expected

Alarm Information
None
Handling Process
None
Root Cause
S93 mirroring realization have following shortcoming:
mirroring at OUT direction of packets happens before packet encapsulate to MPLS frame, so that's why Case 1 and Case 2 display unexpected packets.
Suggestions
If we are need get capture result for MPLS packets, we are need capture them only at INBOUND direction at S93, If configure also OUT direction we will not get correct packets at observe interface.
That shortoming didn't influence to traffic forwarding so it is safe for services.

END