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In one reported run, a single prompt produced annotated captions for all 33 frames of a DNS capture: an annotated PDF, an interactive viewer with packet field trees, and Markdown captions. The author, Sandeep Ahluwalia, reports that the run took about six minutes and 14 VisualEther tool calls, and that each caption was checked against packet fields. The captions are still an AI draft. The capture itself is worth reading closely, because it shows a resolver retrying root queries over TCP after truncated replies.
What the one-prompt run produced
The setup was a folder containing Chris Greer’s dns_full_recursion.pcapng and the prompt annotate dns_full_recursion.pcapng. According to the author’s account of that run, the work went roughly like this:
- Tool path: Claude Code worked through VisualEther’s MCP server.
- Templates: The run generated DNS templates, including one for truncated replies, before captioning.
- Reading order: The flow was read as a whole before any caption was written.
- Outputs: An annotated PDF, an interactive viewer with packet field trees, and Markdown captions.
- Scale: About six minutes and 14 VisualEther tool calls, with matches validated for all 33 frames.
These figures describe one reported run. They are not a benchmark, and they do not show how the same prompt would perform on other captures.
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How the captions were checked
The author ties specific statements to specific packet fields. The table lists the checks described in the article.
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| Check | Frames | What was verified |
|---|---|---|
| EDNS UDP buffer of 512 bytes and DO=1 | 2, 3, 21, 24 | Matched against packet fields |
| Truncation flag (TC) set | 4, 5 | Matched against packet fields |
| UDP length versus DNS message size | Draft caption | Error caught: the draft gave 392 bytes; the DNS message was 384 bytes |
The corrected error is a useful model for DNS captions. The 392 figure is the UDP length field, which counts the 8-byte UDP header along with the DNS message. The DNS message itself is 384 bytes. A caption that mixes these two layers states something true about the wrong part of the packet.
The author’s own caveat is direct: “The captions are an AI draft. Each claim was checked against the packets, but the result still deserves an expert read before anyone publishes it.” Treat the output the same way: useful for navigating a trace, but not a substitute for a reviewer who knows DNS.
What the capture shows
The capture was taken at the resolver. The client sees one request and one answer, while the other 31 frames take place behind the resolver as it works through the lookup for the A record of b2b.infoblox.com. The EventHelix walkthrough of the same trace identifies the servers the resolver contacts as G-root (the root), g.gtld-servers.net (a .com server), and ns5.infoblox.com (the authoritative server for infoblox.com). The final address returned was 8.39.143.138.
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Client to resolver
The client’s query advertises a 1,232-byte UDP buffer and does not set the DNSSEC OK (DO) bit. Its RD bit is set to 1, which asks the resolver to perform recursion on the client’s behalf. The client does not see the upstream work, which is why a resolver-side capture is the more informative vantage point for this lookup.
Resolver’s upstream queries
The resolver’s upstream queries are different. They advertise a 512-byte EDNS UDP size and set DO=1, and they use RD=0 because the resolver is walking the delegation chain itself rather than asking another resolver to do it. The 512-byte limit applies to these upstream queries in this trace. It is not a property of the client’s query.
Truncation and the TCP retry
The root’s two initial replies carry TC=1, meaning they were truncated. A server sets TC when its full answer will not fit in the UDP size the requester advertised, and it expects a retry over TCP. The resolver repeats those queries over TCP, and the full answers arrive at 1,109 and 1,179 bytes. In this capture, the 512-byte advertisement and DO=1 coincide with the truncated root replies and the TCP retries.
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Referrals and glue
Each upstream server answers with a referral rather than a final answer. The root refers the resolver to the .com servers. The .com server refers it to the infoblox.com nameserver, and glue records supply that nameserver’s address, so the resolver can query it directly without a separate lookup. The authoritative server’s reply carries AA=1, which marks it as the zone’s own answer.
The answer returned to the client
Once the resolver has the authoritative answer, it returns the address to the client. The client’s response has AD clear (AD=0), which matters for the DNSSEC question covered below.
Timing in this capture
| Measurement | Value | Scope |
|---|---|---|
| Client query-to-answer duration | 159 ms | This capture only (recorded November 2025) |
| Root TCP retry phase | About 56 ms | This capture only (recorded November 2025) |
| Time for the other phases | Not stated | The EventHelix walkthrough gives no per-hop breakdown |
The retry phase accounts for roughly a third of this lookup’s total time. That proportion comes from one trace. It is not a typical figure for DNS lookups, and it does not show that DNSSEC routinely causes TCP fallback.
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What the trace does not prove
DNSSEC data is visible in the upstream responses: the signatures are present and the DO bit was requested. However, the capture contains no DNSKEY queries, and the client’s response has AD clear. The trace therefore shows DNSSEC-related data being requested and returned. It does not establish that the resolver validated the chain of trust for this answer, and the article should not be read as saying that validation succeeded.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Reading the same capture yourself
To find the events described above in a capture, start with two Wireshark display filters:
The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →dns.flags.truncated == 1shows truncated replies, such as the root’s initial TC=1 responses.tcp.port == 53shows DNS carried over TCP, which covers the retries.
Comparing the UDP query and the TCP retry for the same name shows the difference in advertised buffer sizes and in the answer lengths.
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Capture formats: PCAPNG versus C-DNS
IETF RFC 8618, published in September 2019, describes Compacted-DNS (C-DNS) as a format intended to make collections of DNS messages more efficient to store and transmit. It notes that PCAP and PCAPNG files often include data beyond what DNS traffic analysis requires, and it treats privacy-related filtering as a consideration for capture formats.
The same RFC says conversion back to PCAP can be lossy. Some optional fields may not be recorded, and original IP fragmentation and TCP stream structure may not be recoverable. A C-DNS file is therefore a DNS-message collection, not a full packet capture. If you need transport-level detail such as the TCP exchange in this trace, keep the original PCAPNG.
VisualEther editions for this kind of analysis
VisualEther is EventHelix’s downloadable command-line software for Windows, macOS, and Linux. Its protocol templates include DNS. The vendor’s product page describes three editions and a 45-day trial. Because EventHelix also publishes the walkthrough discussed above, the two are related; Chris Greer has not reviewed or endorsed that walkthrough.
| Edition | Price | Suited to | Stated capabilities | Capture size or page limits |
|---|---|---|---|---|
| Community | Free | Small captures | PDF sequence diagrams | Not stated |
| Professional | Not stated on the product page used here | Individual developers | AI analysis and browser-based triage | Not stated |
| Server | Not stated on the product page used here | Teams running unattended regression analysis | Unattended regression analysis | Not stated |
When comparing editions, the relevant axes are budget, capture size, whether you need AI and triage features, the number of users, and whether you need server or CI use. The trial terms come from the vendor page as it stood when this article was written. Check the official EventHelix site for current terms before you buy or rely on them.
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