Section 7: IP Address Classes

Class D IP addresses range from [...] to [...]

224.0.0.0, 239.255.255.255

The default subnet mask of Class B addresses is [...].

/16

The default subnet mask of Class C addresses is [...].

/24

The network [...] in the Class A space is reserved for loopback address used for testing the local computer.

127.0.0.0 /8

These addresses are valid to be assigned to hosts but they are not routable on the public internet.

(RFC 1918) Private Addresses

This address class is assigned to networks with a very large number of hosts

Class A

This address class is reserved for IP multicast addresses. 

Class D

This address class is ‘experimental and reserved for future use’.

Class E

What is the default subnet mask of Class A addresses?

/8

What is the Class A private IP address range?

10.0.0.0 to 10.255.255.255

What is the Class B private IP address range?

172.16.0.0 to 172.31.255.255

What is the Class C private IP address range?

192.168.0.0 to 192.168.255.255

What is the fundamental trade-off in deciding where the network/host boundary line falls in a subnet mask

A smaller network portion (larger host portion, e.g., /8) yields fewer networks but many hosts per network; a larger network portion (smaller host portion, e.g., /24) yields many networks but fewer hosts per network.

Does the loopback test work only with 127.0.0.1, or with any address in that range?

Any address in the 127.0.0.0/8 range works for loopback testing, not just 127.0.0.1.

What is the long-term solution to IPv4 address exhaustion, and how does its address size compare to IPv4?

IPv6 — a 128-bit address space, compared to IPv4's 32-bit address space.

What is the more commonly deployed workaround for IPv4 address exhaustion in enterprise networks today?

Private IP addresses combined with NAT (Network Address Translation).

Do Class D and Class E addresses have a default subnet mask?

No — neither has a default subnet mask, since they aren't allocated to hosts the way A/B/C are.

What is the special use of the address 255.255.255.255 in the Class E range?

It's the broadcast address for "this network" — a broadcast to whatever local network the source is on.

Do routers forward multicast traffic beyond the local subnet?

Yes, if configured to support it — unlike broadcast traffic, routers will forward multicast to interested receivers on other subnets.

Do routers forward broadcast traffic beyond the local subnet?

No — broadcast traffic does not get forwarded by routers by default and stays within its own local subnet.

On a local subnet, does multicast traffic reach every host, or only interested hosts?

Only interested hosts (those that have requested/subscribed to the multicast stream) — unlike broadcast, which reaches every host on the subnet regardless of interest.