Mirroring can be implemented on SAPs or ingress network interfaces. The Flexible Fast Path processing complexes preserve the original packet throughout the forwarding and mirroring process, making any necessary packet changes, such as adding encapsulation, on a separate copy.
Mirroring supports multiple types of destinations including local SAPs, remote tunnels, and FTP servers in PCAP format.
Nokia’s implementation of packet mirroring is based on the following assumptions:
Ingress and egress packets are mirrored as they appear on the wire. This is important for troubleshooting encapsulation and protocol issues.
When mirroring at ingress, the Flexible Fast Path network processor array (NPA) sends an exact copy of the original ingress packet to the mirror destination while normal forwarding proceeds on the original packet.
When mirroring is at egress, the system performs normal packet handling on the egress packet, encapsulating it for the destination interface. A copy of the forwarded packet is forwarded to the mirror destination. Because the mirror copy of the packet is created before egress queuing, the mirrored packet stream may include copies of packets that are discarded in egress queues, such as during congestion or rate limiting.
Remote destinations are reached by encapsulating the ingress or egress packet within an SDP, like the traffic for distributed VPN connectivity services. At the remote destination, the tunnel encapsulation is removed and the packet is forwarded out a local SAP.