Mirroring can be configured for ingress or egress on specific service entities (for example: SAPs, ports, filter entries), which are referred to as mirror sources. A mirror copy of the packet is sent out of the mirror destination, which can be either a local mirror destination or remote mirror destination. For platform-specific support information about mirror sources and mirror destinations, see Mirror sources and destinations.
The Nokia implementation of packet mirroring is based on the following assumptions:
When mirroring at ingress, ingress packets are mirrored as they appear on the wire. A copy of the ingress packet is encapsulated and sent to the mirror destination. Except for adding the required encapsulations, the content of the original packet is unchanged. The system performs normal packet handling and forwards the original packet to its destination. This behavior is important for troubleshooting encapsulation and protocol issues.
There are some exceptions to this behavior; for example, on the 7210 SAS-K 2F6C4T and 7210 SAS-K 3SFP+ 8C all packets received by the ingress processing pipeline are mirrored, whereas packets dropped by the pre-classifier modules are not mirrored. For more information about exceptions, see the 7210 SAS Software Release Notes 22.x.Rx.
When mirroring at egress on the 7210 SAS-K 2F1C2T, 7210 SAS-K 2F6C4T, and 7210 SAS-K 3SFP+ 8C, the mirrored packet is an exact copy of the forwarded packet. A mirror copy of the packet is created after the packet is processed by egress QoS, but before it is sent out to the wire.
When mirroring at egress on the 7210 SAS-D and 7210 SAS-Dxp, the mirror packet is not an exact copy of the forwarded packet. The mirror packet contains an internal VLAN tag and does not contain the SAP tags contained in the forwarded copy of the packet. Because the mirror copy of the packet is created at egress before it is processed by egress QoS, the packet may be dropped by egress QoS mechanisms (such as RED mechanisms and so on) and may not be forwarded. However, the dropped packet is still mirrored.
On the 7210 SAS-K 2F6C4T and 7210 SAS-K 3SFP+ 8C, mirroring supports remote destinations as follows:
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.