Consider the following arrangement of Ethernet switches (bridges) S1-S7 and hosts A-E. Each switch has a forwarding table of host,interface pairs; each table is initially empty. When a bridge sees a packet, it adds the sending host to the table, with the interface by which the packet arrived, if it was not there already.

S7------E | | A--------S1--------S2--------S3--------C | | | | B--------S4--------S5--------S6--------D

Initially all the tables are empty, and then the following transmissions occur in sequence. After the indicated transmissions below, some (but not necessarily all) of the switches see the packet and thus learn about the senders location and add the sender to their table; these tables affect how subsequent transmissions are handled. You are to indicate, after each transmission, which switches S1S7 saw the packet (and thus learned the location of that sender, if it didn't know already). For example, in the first two rows, no table contains the destination E and so the packets are forwarded to all switches and so all switches are marked YES; a consequence is that all switches now have B and C entered into their tables. It may help to label routers S1-S7 with senders ABCDE they have seen.

transmission	S1 sees	S2 sees	S3 sees	S4 sees	S5 sees	S6 sees	S7 sees
B sends to E	yes	yes	yes	yes	yes	yes	yes
C sends to E	yes	yes	yes	yes	yes	yes	yes
E sends to C
D sends to B
C sends to D
A sends to E
D sends to A