Subnetting Practice: Valid Host for 192.168.4.32/68 (IPv4)
We need to decide which candidate IPs belong to the network defined as 192.168.4.32/68. The core idea is that a CIDR prefix length of /68 means the first 68 bits are the network portion, and the remaining bits are host bits. For IPv4, addresses are 32 bits total, so a prefix length greater than /32 is not valid for IPv4. As a result, no IPv4 host can be validly matched to 192.168.4.32/68 in standard CIDR notation.
In other words, the given expression “192.168.4.32/68” is invalid for IPv4, so there is no correct choice among (i)–(iv) under normal IPv4 subnetting rules.
Mermaid reasoning view:
Key terms
- CIDR
- Prefix length
- Subnet mask
- Network address
- Broadcast address
type="warning" title="Warning: /68 is not a valid IPv4 prefix" content="IPv4 has 32 bits, so CIDR prefix lengths must be in the range to . A prefix like /68 implies more bits than exist in IPv4 addressing."
How to check whether a candidate host is inside a CIDR network
- 1Step 1
Confirm the prefix length is valid for the address family. For IPv4, allowed prefix lengths are 0 through 32.
- 2Step 2
If valid, compute the subnet mask, then derive the network address and broadcast address.
- 3Step 3
If the candidate IP is between the network address and broadcast address (inclusive of network, exclusive of broadcast for usable hosts), it belongs to the subnet.
- 4Step 4
Select the candidate(s) that fall within the computed subnet range.
Applying the process:
- The prefix is /68.
- For IPv4, the address is 32 bits, so /68 cannot be expressed in IPv4 CIDR.
- Therefore, the network 192.168.4.32/68 is not a valid IPv4 subnet, and none of the candidate IPv4 addresses (192.168.4.39, .50, .47, .31) can be determined to be valid hosts for an invalid subnet definition.
Options evaluation (result)
- (i) 192.168.4.39 → cannot be validated as a host because the subnet is invalid
- (ii) 192.168.4.50 → cannot be validated as a host because the subnet is invalid
- (iii) 192.168.4.47 → cannot be validated as a host because the subnet is invalid
- (iv) 192.168.4.31 → cannot be validated as a host because the subnet is invalid
Subnet Validation to Host Selection (IPv4)
Read the CIDR
1) InputTake the form IP/prefix-length (here: 192.168.4.32/68)."
Check prefix length range
2) Validity checkIPv4 prefix must be between 0 and 32."
Compute subnet boundaries
3) Network math (only if valid)Derive network and broadcast, then test candidates."
Pick valid host option(s)
4) AnswerIf CIDR is invalid, no option can be correct under IPv4 CIDR rules."
Candidate Host Membership (Outcome)
Because the CIDR 192.168.4.32/68 is invalid for IPv4, membership is undefined/invalid for all candidates.
Common edge cases & clarifications
Knowledge Check
In IPv4 CIDR notation, which prefix lengths are valid?