Mirroring can be configured on ingress or egress of certain service entities (For example, SAPs, ports, filter entries) and they are referred to as mirror sources. For more information, see the Mirror source and destinations.
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, an exact copy of the original ingress packet is sent 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 (as seen on the wire) is forwarded to the mirror destination, as follows:
On the 7210 SAS-Mxp, 7210 SAS-Sx/S 1/10GE, 7210 SAS-R6 with IMMV2, 7210 SAS-R12, the mirror copy of the packet is a copy of the forwarded copy.
On the 7210 SAS-T and 7210 SAS-Sx 10/100GE, the mirror copy of the packet is not a exact copy of the forwarded copy in case of port egress mirroring.
On the 7210 SAS, mirroring at egress takes place before the packet is processed by egress QoS. Hence, there exists a possibility that a packet is dropped by egress QoS mechanisms (because of RED mechanisms and so on) and therefore not forwarded, but it is still mirrored.
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.