• The Header that gets attached to the packet is 38 bytes long. In case of a packet with L3 VLAN, it would be 42 bytes long.The original payload /original mirrored data starts from the 39th byte in a given ERPM packet. The first 38/42 bytes of theheader needs to be ignored/ chopped off.• Some tools support options to edit the capture file. We can make use of such features (for example: editcap ) and chop theERPM header part and save it to a new trace file. This new file (i.e. the original mirrored packet) can be converted back intostream and fed to any egress interface.b Using Python script• Either have a Linux server's ethernet port ip as the ERPM destination ip or connect the ingress interface of the server to theERPM MirrorToPort. The analyzer should listen in the forward/egress interface. If there is only one interface, one can choosethe ingress and forward interface to be same and listen in the tx direction of the interface.• Download/ Write a small script (for example: erpm.py) such that it will strip the given ERPM packet starting from the bitwhere GRE header ends. Basically all the bits after 0x88BE need to be removed from the packet and sent out through anotherinterface.• This script erpm.zip is available for download at the following location: http://en.community.dell.com/techcenter/networking/m/force10_networking_scripts/20438882.aspx• Unzip the erpm.zip and copy the erpm.py file to the Linux server.• Run the python script using the following command:python erpm.py -i interface> -o erpm.py : This is the script downloaded from the script store. : Specify the interface id which is connected to the mirroring port or this should be interface whose ip address hasbeen specified as the destination ip address in the ERPM session. : Specify another interface on the Linux server via which the decapsulation packets can Egress. In case there is onlyone interface, the ingress interface itself can be specified as Egress and the analyzer can listen in the tx direction.Port Monitoring on VLTDevices on which VLT is configured are seen as a single device in the network. You can apply port monitoring function on the VLT devicesin the network.Port monitoring enables ingress or egress traffic traversing on a port to be sent to another port so that the traffic can be analyzed. Theport to which traffic is sent for analysis is called the mirroring port. This port is connect to a port analyzer, which performs the trafficanalysis function.Depending up on the location of the port to which the port analyzer is connected, port monitoring is classified into three categories: localPort mirroring, remote port mirroring (RPM), and encapsulated remote port mirroring (ERPM).NOTE: For more information on port monitoring, see Port Monitoring.The port monitoring or mirroring function when applied to VLT devices works as expected except with some restrictions. You can configureRPM or ERPM monitoring between two VLT peers. As VLT devices are seen as a single device in the network, when a fail over occurs, thesource or destination port on one of the VLT peers becomes inactive causing the monitoring session to fail. As a result, Dell Networking OSdoes not allow local Port mirroring based monitoring to be configured between VLT peers. However, you can create local Port mirroringmonitoring sessions separately on individual devices that are a part of the VLT configuration.NOTE: For more information on configuring VLT, see ConfiguringVLT.VLT Non-fail over ScenarioConsider a scenario where port monitoring is configured to mirror traffic on a VLT device's port or LAG to a destination port on some otherdevice (TOR) on the network. When there is no fail over to the VLT peer, the VLTi link (ICL LAG) also receives the mirrored traffic as the708 Port Monitoring
