Hello Rong
I assume this is the question about packet flow that you were asking about in this post?
In any case, I assume that the originating host is connected to the switch and is not the switch itself. Also I assume the destination is some host that is on the network that is connected to interface Ge1/1 on R1. Remember, defining the source and destination devices is important to determine packet flow.
- The packet enters a port on SW1 and the destination MAC is read. The destination MAC should be that of R3. The switch does a MAC address table lookup, determines the exit port, and sends it to R3.
- R3 receives it, decapsulates it to Layer 3, reads the destination IP, routes it, and determines that the exit interface should be Ge1/1. It is recapsulated, source and destination MACs are used from R3 and R2, respectively, and it is sent.
- R2 receives it, decapsulates it to Layer 3, reads the destination IP, routes it, and determines that the exit interface should be Ge0/1. It is recapsulated, source and destination MACs are used from R2 and R` respectively, and it is sent.
- R1 receives it, decapsulates it to Layer 3, reads the destination IP, routes it and determines that it is on the subnet connected to the Ge1/1 interface. It recapsulates it with the source MAC of R1 and the destination MAC of the destination host and sent out of Ge1/1.
- The frame is received by the destination host.
I hope this has been helpful!
Laz