Hello Asoltanian,
1)There is an Interesting point in it, Can we use LACP interface as Port-Mirror destination?
Although I haven't tested this scenario (and may be completely wrong here), I suspect you should be able to use ae interface (configured with or without LACP) as the port-mirroring destination.
2) When Juniper says Port-Mirror is supported on one particular MPC, what does this mean? Does it mean Port-Mirror destination or Source?
It would've been easier to tell if you'd provided the link you referred to. In context of port-mirroring feature, probably it means support on FPC where port-mirroring action actually takes place. Depending on your scenario and configuration, it may happen on ingress or egress FPC which forward the original packet that will be mirrored.
3) Is term "FPC" equal to "MPC" in this feature?
Speaking about MX, yes. In the past both DPCs and MPCs were used in MX (and some customers still use DPCs), but nowadays only MPCs are supported and you can use terms FPC and MPC interchangeably.
Best regards,
Sergii
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