Q$1.$ Ethernet Learning Algorithm

Suppose we have the Ethernet switches S$1$ through S$4$ arranged as below. All forwarding tables are empty; each switch uses the learning algorithm described in Section $2\mathrm{.}4\mathrm{.}1.$

Now suppose the following packet transmissions take place in order:

$-$First A sends to B; $-$Then B sends to A; $-$Then C sends to B; $-$Finally D sends to A$.$

For each switch S$1$ to S$4,$ list what source MAC addresses $($eg A$,$ B$,$ C$,$ D$)$ it has seen $($and thus what nodes it has learned the location of$).$

Repeat question $1)$ with the same network layout, except that instead the following packet transmissions take place in order:

$-$First A sends to D; $-$ Then D sends to A; $-$ Then A sends to B; $-$Finally B sends to D$.$