Subnet Boundary Desk
How to check a subnet?s boundary addresses in Subnet Boundary Desk
Enter an IPv4 address and a separate prefix, paste candidate addresses one per line, then choose Analyze. Subnet Boundary Desk includes both the first and last address in its block: the example puts 192.168.10.64 and 192.168.10.127 Inside 192.168.10.64/26. This checks mathematical membership only; it does not establish whether an address is assignable or a device is reachable.
Load four addresses around one block
Choose Use example to fill IPv4 address with 192.168.10.77 and Prefix / with 26. The candidate list contains 192.168.10.63, 192.168.10.64, 192.168.10.127 and 192.168.10.128, in that order. Loading fills the fields and clears any previous result; choose Analyze to calculate.
The canonical block is 192.168.10.64/26. Its first inclusive address is 192.168.10.64, its last is 192.168.10.127, and its total is 64 addresses. The subnet mask is 255.255.255.192 and the wildcard mask is 0.0.0.63. Use these facts to check which block the app actually calculated before reading candidate decisions.
Read Inside separately from address usability
The example produces two Inside and two Outside decisions. The address ending in .63 falls immediately before the block; .128 falls immediately after it. The entries ending in .64 and .127 are Inside and carry First boundary and Last boundary labels respectively. Equality with either edge passes the membership check.
Inside means that the candidate?s numeric address lies between the two inclusive boundaries. The app does not subtract addresses for conventional network or broadcast reservations. It also does not ping, inspect devices or recommend routes. Use the result to answer ?does this address fall in this block?? Keep questions about assignment or connectivity separate.
Distinguish the entered address from the block start
The example?s entered address ends in .77, but its canonical block starts at .64. ?Entered address equals network boundary: No? is therefore expected. It is an equality check against the first address, not a warning that the input is outside its calculated block.
For this /26, six bits remain after the prefix, giving a block size of 64. The calculation groups addresses into blocks of that size and finds the one containing the input. To see the equality label change, replace only the entered address with 192.168.10.64 and analyze again. The canonical block and the four candidate decisions stay the same; the equality becomes Yes.
Replace the example with your own list
Enter the address and prefix in separate fields: use 192.168.10.77 and 26, rather than pasting 192.168.10.77/26 into the address field or typing /26 into Prefix /. Addresses require four decimal octets from 0 to 255. Surrounding whitespace is trimmed, but leading-zero octets such as 010, hostnames and IPv6 are rejected.
Paste one candidate address per line. Blank lines are ignored, but the result retains physical source line numbers and keeps duplicates in their original order. If the same Inside address appears twice, it contributes two to the Inside count. Those totals count entries, not distinct addresses or discovered devices.
One invalid candidate rejects the whole analysis and identifies its source line; the app preserves your inputs for correction. Fix that line and choose Analyze again. The list is limited to 100 nonblank lines and 8192 UTF-8 bytes, including whitespace. Candidates are optional if you only need the block facts.
Save the result before changing or leaving it
After a successful analysis, choose Download .txt to request subnet-boundary-report.txt. The report includes the original inputs, block facts, bits and every candidate decision. Original input strings are JSON-quoted, so escaped line endings in that part of the report preserve the submitted text rather than indicating a candidate error.
Any input edit clears the result and disables download until another successful analysis. Save a useful report before comparing a different prefix. If browser saving is blocked, open Complete selectable report and select its text manually. Reset all or reloading discards the tab?s inputs and results; there is no saved history to restore.
AI-assisted ForgeHub editorial. App capabilities were checked against its implementation; this guide is not an independent review.
Frequently asked questions
Must I enter the first address of the subnet?
No. The app calculates the containing block from any accepted IPv4 address and prefix. In the example, 192.168.10.77 with prefix 26 produces 192.168.10.64/26. The boundary equality label only tells you whether your entered address equals that block?s first address.
Why does a /31 show two addresses and a /32 show one?
The app counts the complete inclusive mathematical block without reservation deductions. A /31 has two addresses. A /32 has one address, and a matching candidate is labelled First and last boundary.
Can I paste candidate addresses with their own prefixes?
No. Each candidate must be a dotted-decimal IPv4 address without a prefix suffix. The separate Prefix / field defines the single block against which every candidate is checked.
Does Inside mean a device is online?
No. Inside is a mathematical membership decision. No device is contacted, and the app performs neither DNS nor ping.