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Subnetting, CIDR, and VLSM

11 questions. Nothing is recorded — answers are graded and shown, not stored.

How many addresses can be assigned to interfaces on a /26?
- 64
- 62
- 63
- 60
The two formulas that cover most subnetting arithmetic are 2^n and 2^n minus 2. What decides which one applies?
- Whether the network is classful or classless
- Whether the prefix is longer or shorter than /24
- Whether you are counting hosts or counting networks — hosts count host bits and subtract two, networks count network bits and subtract nothing
- Whether broadcast is in use on the segment
A host with address 10.10.10.10 and mask 255.255.255.0 wants to send to 10.10.20.5. What does it do with the mask, and what does it conclude?
- It ANDs both addresses with the mask, gets 10.10.10.0 and 10.10.20.0, and sends the packet to its default gateway
- It ANDs both addresses with the mask, gets the same result, and delivers directly on the local segment
- It compares the addresses digit by digit, finds the first two octets match, and delivers directly
- It ORs the destination with the mask to produce the broadcast address and sends there
Which of these is not a valid subnet mask?
- 255.255.255.128
- 255.255.240.0
- 255.255.255.192
- 255.255.253.0
What does writing 10.10.10.10/24 give you that writing 10.10.10.10 with mask 255.255.255.0 does not?
- A different network/host boundary, since prefix lengths and masks are not equivalent
- The same information more compactly, and without any reference to an address class
- Automatic route aggregation, which dotted masks cannot express
- A boundary that a router can change dynamically, which a fixed mask cannot
Can 10.1.0.0/16 and 10.2.0.0/16 be advertised as a single aggregate route?
- Yes — they are adjacent, so 10.1.0.0/15 covers both
- Yes — any two /16s inside the same /8 aggregate to a /15
- No — they are adjacent, but a /15 starting at 10.0.0.0 covers 10.0 and 10.1, and no /15 boundary contains 10.1 and 10.2
- No — aggregation only works between blocks with different prefix lengths
You are dividing 10.10.10.0/24 for three segments needing 45, 25, and 10 hosts. Why allocate the largest first?
- Because the largest segment is usually the most important and should get the lowest addresses
- Because smaller subnets cannot be placed after larger ones without renumbering
- Because allocating smallest first leaves the larger blocks without a correctly aligned boundary to start on
- Because routers process routes in descending order of prefix length
A segment needs 45 usable addresses. What is the shortest prefix that is not wasteful — that is, the smallest block that fits?
- /25, giving 126 usable
- /27, giving 30 usable
- /24, giving 254 usable
- /26, giving 62 usable
Beyond conserving addresses, what does dividing a network into subnets buy you?
- A natural boundary at which to enforce policy between systems with no reason to talk, and a bound on broadcast traffic
- Encryption between subnets, since traffic crossing a router is protected in transit
- Automatic failover, because a router will reroute around a failed subnet
- Higher link speed within each subnet, because there is less contention on the wire
You ping your network’s broadcast address and get two replies on a segment you know has a dozen hosts. What should you conclude?
- Ten hosts are down or unplugged
- The broadcast address was calculated incorrectly, since a correct one reaches everything
- Little — many systems ignore broadcast pings, so a quiet result is not proof of an empty network
- The router is filtering broadcast traffic within the segment
Given the reason for learning the arithmetic by hand, what is the argument for using ipcalc in day-to-day work?
- There is none — hand calculation is the professional standard and tools are a crutch
- The manual method exists to make a wrong mask recognisable on sight; once you have that, the tool is faster and does not misread
- The tool handles VLSM, which cannot be worked out by hand
- The tool is required because prefix lengths above /24 have no dotted-mask equivalent