An Introduction to Port Mirroring in Broadcom Switches

Port Mirroring:

                Port mirroring is a way to redirect a copy of packets coming to (ingress) or going out (egress) of a port to another port. It will be helpful to analyze the correctness/content of a packet and it can be used as a best debugging method.

Example:

Consider the below scenario.

        In the above topology, two networks are connected via a router. Now, if we want to capture the traffic that flows between these two networks without disturbing the connections, then port mirroring will be helpful. Here we can mirror the traffic of either Port 1 or Port 3 to Port2. So we can analyze the traffic content without disturbing the topology.

Port Mirroring commands in BCM:

                The below commands are used to enable the port mirroring functionality in Broadcom switches.

S.No	Command	Purpose
1	mirror mode=l2 port=x	This command will do mirroring of all traffic from all ports to port "x". The mode can accept the value of l2 or l3.
2	mirror mode=l2 port=x IngressBitMap=y	All the incoming packets to port “y” will be mirrored to port “x”. It is not necessary that both port “x” & “y” to be in the same VLAN.
3	mirror mode=l2 port=x EgressBitMap=y	All packets going out of port “y” will be mirrored to port “x”.
4	mir	It will display the current port mirror settings.
5	help mirror	It will display the help on the port mirroring commands