ERPM Behavior on a typical Dell Networking OSThe Dell Networking OS is designed to support only the Encapsulation of the data received / transmitted at the specified sourceport (Port A). An ERPM destination session / decapsulation of the ERPM packets at the destination Switch are not supported.Figure 108. ERPM BehaviorAs seen in the above figure, the packets received/transmitted on Port A will be encapsulated with an IP/GRE header plus a new L2header and sent to the destination ip address (Port D’s ip address) on the sniffer. The Header that gets attached to the packet is 38bytes long.If the sniffer does not support IP interface, a destination switch will be needed to receive the encapsulated ERPM packet and locallymirror the whole packet to the Sniffer or a Linux Server.Decapsulation of ERPM packets at the Destination IP/ Analyzer• In order to achieve the decapsulation of the original payload from the ERPM header. The below two methods are suggested :a. Using Network Analyzer– Install any well-known Network Packet Analyzer tool which is open source and free to download.– Start capture of ERPM packets on the Sniffer and save it to the trace file (for example : erpmwithheader.pcap).– The Header that gets attached to the packet is 38 bytes long. In case of a packet with L3 VLAN, it would be 42 byteslong. The original payload /original mirrored data starts from the 39th byte in a given ERPM packet. The first 38/42bytes of the header 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 chopthe ERPM header part and save it to a new trace file. This new file (i.e. the original mirrored packet) can be convertedback into stream and fed to any egress interface.Port Monitoring 657
