CCNA quiz 2: IP addressing and subnetting

A /26 leaves 6 host bits: 2^6 = 64 addresses, minus the network and broadcast addresses = 62 usable hosts.

/27 means 27 bits on: 24 bits (255.255.255) plus 3 bits in the last octet (128+64+32 = 224).

The block size for /27 is 32 (256 − 224). Multiples of 32: 0, 32, 64, 96. 77 falls in the block starting at 64.

A /25 splits the last octet into 0–127 and 128–255. 130 is in the upper half, so the broadcast is 10.1.1.255.

The private ranges are 10.0.0.0/8, 172.16.0.0/12 (172.16–172.31) and 192.168.0.0/16. 172.20.x.x is inside the 172.16.0.0/12 block.

A /26 gives 62 usable hosts, enough for 50. A /27 gives only 30. A /25 works but wastes more addresses.

A wildcard mask is 255 minus each mask octet: 255 − 240 = 15, so 0.0.0.15.

A /31 has just two addresses, both usable on a point-to-point link. /30 (two usable hosts) is the older common choice.

IPv6 addresses are 128 bits, written as eight groups of four hexadecimal digits. IPv4 addresses are 32 bits.

FE80::/10 is link-local (used on one link only). 2000::/3 is global unicast, FC00::/7 is unique local and FF00::/8 is multicast.

A /28 leaves 4 host bits: 2^4 = 16 addresses, minus the network and broadcast addresses = 14 usable.

/21 = 8 + 8 + 5 bits. The third octet has 5 ones: 128+64+32+16+8 = 248, so 255.255.248.0.

/26 blocks are 64 addresses: .64 to .127. Of the options, only .100 falls in 172.16.5.64/26.

The network address is .64, so the first usable host is .65. The block runs to .95 (broadcast).

The /12 private block covers 172.16.0.0 to 172.31.255.255 (RFC 1918).

Drop leading zeros in each group and replace one run of all-zero groups with ::. The :: may appear only once.

127.0.0.0/8 is reserved for loopback. 127.0.0.1 always refers to the local host itself.

Borrowing 2 bits (from /24 to /26) gives 2^2 = 4 subnets of 64 addresses each.

PAT tracks each inside connection by translating its source port, so many hosts can share one public address.

Global unicast addresses, routable on the internet, come from 2000::/3. Link-local is FE80::/10, unique local FC00::/7 and multicast FF00::/8.