Traffic Mirroring Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Release

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Guidelines for mirroring buffer drop packets

Updated: March 2, 2026

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Overview

This section explains the operational guidelines and constraints for mirroring buffer drop packets, including interface support, session limits, and specific drop reasons. These rules ensure proper configuration of SPAN to file and ERSPAN sessions for traffic monitoring.

These guidelines apply to mirroring buffer drop packets:

  • SPAN to File Buffer drop is a global configuration, not specific to any interface.

  • Mirroring of buffer drop packets is supported only on the ingress interface.

  • Only the packets dropped by the reasons TM_EXACT_METER_DROP and TM_STATISTICAL_METER_DROP are mirrored.

  • Maximum of one drop session with destination as Span to File and one drop session with destination as ERSPAN can be configured globally per router.

  • From Release 24.2.11, one forward-drop session and one TM buffer drop session are supported for file and GRE tunnel interface destinations.

  • For ERSPAN sessions that monitor buffer drop packets, a default value of 0 is used for the encapsulation traffic class, irrespective of the DSCP value assigned for the tunnel.

  • ERSPAN counters are not updated for buffer drop packets.