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Information on remote port mirroring on Junos routers doesn’t seem to be very easy to come by for some reason – there is quite a lot of information about doing this on EX switches (a bit like RSPAN in Cisco’s IOS), which wasn’t what I needed. Various other sources of information (such as Cluepon) say this can be done using a GRE tunnel, but that the capturing device needs to be a server that terminates the GRE tunnel – which all seemed a bit complicated.
I needed to remotely mirror a port on an MX to a second MX where a windows-based Wireshark was connected, so getting GRE working to a Windows host sounded like a non starter.
So I had to work it out myself – and hopefully this write-up will prove useful to someone else in the future.
An additional requirement for the customer was that the captured interface should be in a VRF, so the test-bed I set up below has production traffic flowing through a VRF, and the mirrored traffic in a GRE tunnel which is running in the global routing table.
Here’s the write-up I did for the customer: