10 — Practice solutions
These are independently written explanations, not an official marking scheme.
10A
Mask 255.255.255.192; network 192.168.12.64; broadcast 192.168.12.127; usable 192.168.12.65–126; 2⁶−2 = 62 usable hosts. Address .130 is in the .128–191 block, so it is not in the same /26 subnet.
Reasoning
/26 leaves6 host bits and fixes two bits of the final octet. Blocks therefore begin at 0,64,128,192. The value 77 lies in 64–127. The value 130 belongs to the next block; sharing the first three octets is insufficient when the prefix is /26.
10B
Packet switching lets other traffic use links when the email sender is idle; a dedicated circuit reserves resources even during those gaps. Shared queues can cause variable delay, loss or out-of-order delivery. For a remote server, the host needs its default gateway’s local MAC address, normally found using ARP; the server remains the IP destination.
Reasoning
Email is intermittent, so a continuously reserved circuit can sit idle between bursts. Packet switching shares that unused capacity. The MAC question concerns the first local hop, not the email service’s port or remote server’s link address.