Enterasys Networks ENTERASYS ATX - Manual (Page 68)

ATX Port Mirroring
6-2 The Port Mirroring Window
Oversized packets might be produced when mirrored traffic is sent from an 802.5
interface to an 802.3 interface (i.e., an 802.5 frame, when mirrored to an 802.3
interface, must have its MAC address reversed and a length field must be added;
the translation process may increase the frame size so that it exceeds the size of
the maximum transport unit (MTU) of the diagnostic port). By discarding or
truncating such oversized packets, you can avoid overloading the diagnostic
interface, and further reduce any latency in your mirrored traffic.
The ATX’s mirroring software attempts to replicate mirrored packets as closely as
possible. Certain physical layer information, such as 802.5 Access Control and
Frame Control bytes, is not reproduced since it is not generally of interest when
examining mirrored traffic. MAC layer information, with the possible exception
of any necessary framing translation, is reproduced exactly. Network layer
information is also unmodified. Bridging packets are reproduced in their original
order. Routed packets are mirrored prior to any alteration by the ATX’s routing
software, and may be out of order, as is sometimes the case with normally routed
packets.
The Port Mirroring Window
To invoke the Port Mirroring window:
1. Click on the PPE’s Module Index (Module 1). The Module menu will appear.
2. Drag down Port Mirroring..., and release.
TIP
In order to reproduce mirrored traffic as faithfully as possible (i.e., reduce the number of
dropped or truncated frames), it is recommended that the media type and framing protocol
of your mirrored ports and your diagnostic port be identical. We also recommend that the
speeds of all involved ports be identical, or at least that your diagnostic port operate at a
higher speed than your mirrored port(s).