Side-by-Side DNS Comparison Without Live Queries
When troubleshooting DNS changes, relying on live network queries can introduce variables like local caching, network latency, and regional routing differences. The DNS Propagation Checker provides a static, side-by-side comparison of DNS answers that you have already retrieved from different resolvers. By pasting these records directly into the tool, you can analyze differences in record types, Time To Live (TTL) values, and record data without sending new DNS queries over the network.
This tool is designed for site maintainers, developers, and anyone who has obtained text answers from two or three DNS resolvers and needs to verify consistency. Because the tool does not query live DNS servers, it operates entirely on the data you provide.
Input Formats and Validation Rules
To perform a comparison, you must input DNS records for at least two resolvers. The tool accepts two primary record formats, which are parsed line by line:
- Standard dig answer lines: These follow the standard output format of the
digcommand-line utility, structured asname TTL IN type value(for example,example.com. 300 IN A 192.0.2.1). - Compact lines: A simplified format structured as
type TTL value(for example,A 300 192.0.2.1).
During processing, any comments and dig section headings included in your pasted text are ignored. However, the input must conform to these structures and size limits to prevent processing errors:
- Character Limit: Each resolver answer must be under 100,000 characters. If an input exceeds this, the tool displays the error:
Resolver ‹n› answer is unusually large. Keep it under 100,000 characters. - Format Validation: If a line does not match either supported format, the tool displays:
Resolver ‹n›, line ‹line› is not a supported DNS record. Use name TTL IN type value, or type TTL value. - Minimum Inputs: If you click "Compare answers" without pasting any data, the tool returns:
Paste at least two resolver answers. If you populate only one resolver panel and attempt to run the comparison, the interface displays:Paste an answer into at least two resolver panels.
Clicking "Clear" resets the tool, clearing all resolver answers, resetting the results display, and returning the input focus to the first answer field.
Interpreting Comparison Results
Once you provide at least two valid resolver answers and run the comparison, the tool generates a "Side-by-side comparison" table. The output categorizes the relationship between the records using specific status labels:
| Status Label | Meaning |
|---|---|
| Exact match | The record type, TTL, and value are completely identical across all compared resolvers. |
| TTL differs | The record type and value match exactly, but the TTL values vary between the resolvers. |
| Values differ | The record type is identical, but the returned values (such as IP addresses or mail server targets) are different. |
| No record | A specific record type that exists in one or more resolver answers is completely missing from another resolver's answer. |
At the bottom of the comparison, a summary line reads: Compared ‹types› record types across ‹resolvers› resolver samples.
Understanding TTL Variations and Cache Ages
When comparing DNS records, seeing different TTL values for the same record is a common occurrence. A status of "TTL differs" does not necessarily mean your DNS configuration is incorrect or that the zone files are out of sync.
Recursive DNS resolvers query authoritative nameservers and cache the results for the duration specified by the record's TTL. As time passes, the resolver counts down this TTL value until it reaches zero, at which point it discards the cached record and fetches a fresh copy from the authoritative source. If you query two different resolvers at different times, or if they cached the record at different times, their remaining TTLs will differ. Therefore, matching values with different TTLs usually indicate different cache ages rather than different zone data.
Limitations of Local DNS Comparisons
While comparing resolver outputs side-by-side is highly effective for identifying discrepancies between specific datasets, it is important to understand the boundaries of this analysis:
- No Live Queries: The tool does not contact external DNS servers or authoritative nameservers. It compares only the samples you manually paste into the interface.
- No Proof of Global Propagation: A matching result across your samples does not prove worldwide DNS propagation. Other public, ISP, corporate, or local device caches may still hold older records.
- No Authoritative Validation: The tool cannot verify if the records are authoritatively correct or predict exactly what record a specific end-user will receive.
Local Browser Processing and Privacy
Your data privacy is maintained during the comparison process. All parsing, validation, and comparison of your pasted DNS answers happen directly in your browser. No data is uploaded to or saved by BroBroGo.
Frequently Asked Questions
Which DNS result formats can I paste?
Paste standard dig answer lines such as “example.com. 300 IN A 192.0.2.1” or compact lines such as “A 300 192.0.2.1”. Comments and dig section headings are ignored.
Does a different TTL mean the DNS value is wrong?
Not necessarily. Recursive resolvers count down cached TTLs and may apply their own cache limits. Matching values with different TTLs usually show different cache ages, not different zone data.
Does a match here prove DNS has propagated everywhere?
No. The comparison covers only the answers you paste. Other public, ISP, company and device caches may return different data, and this page does not contact authoritative nameservers.