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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesIn the run Sandeep Ahluwalia describes, one prompt, annotate dns_full_recursion.pcapng, produced captions for all 33 frames of a resolver-side DNS capture, along with an annotated PDF, an interactive viewer, and Markdown captions. The output is an AI draft. The author checked claims against packet fields, found and fixed at least one error, and still recommends an expert read before publication. The capture itself is more instructive than the tool run: it shows a resolver that hit truncated root replies, retried over TCP, and walked referrals from the root to an authoritative server.
What the one-prompt run did
The setup was a folder containing a capture file named dns_full_recursion.pcapng, which comes from Chris Greer’s material, and a single instruction to Claude Code. According to the author’s account, Claude Code used the VisualEther MCP server to do the following:
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- Generated DNS templates, including one for truncated replies.
- Validated template matches against all 33 frames.
- Read the whole flow before writing any caption.
- Produced three outputs: an annotated PDF, an interactive viewer with packet field trees, and Markdown captions.
The author reports the session took about six minutes and used 14 VisualEther tool calls. These figures describe that one run. They are not a benchmark, and no independent replication is reported.
How the field checks worked
Each caption was tied to fields in the packets. The author reports checks on the 512-byte EDNS UDP buffer and the DO (DNSSEC OK) bit in frames 2, 3, 21, and 24, and on the truncation flag (TC) in frames 4 and 5.
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The validation step also caught a real mistake. A draft caption gave 392 bytes for the message. The correct DNS message length was 384 bytes; 392 is the UDP length, which adds the 8-byte UDP header. The difference looks small, but it is exactly the kind of error that matters when a reader uses captions to reason about the protocol. Keep statements tied to the correct layer: UDP length, UDP payload, and DNS message are three different numbers.
In the author’s words: “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.”
What the capture shows
The capture was recorded at the resolver, so it contains the resolver’s upstream conversation as well as the client’s request and final answer. Per the EventHelix walkthrough of the same trace, the client asks for the A record of b2b.infoblox.com. The resolver then queries three kinds of server in turn:
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| Step | Server (as identified in the walkthrough) | Role in this lookup |
|---|---|---|
| 1 | G-root | Root server; returns a referral toward .com |
| 2 | g.gtld-servers.net |
.com server; returns a referral toward infoblox.com |
| 3 | ns5.infoblox.com |
Authoritative server for infoblox.com; returns the final answer with AA=1 |
The final address returned was 8.39.143.138. The server identities come from the capture and its glue records, as the walkthrough explains them.
The client side versus the resolver side
The client’s query advertises a 1,232-byte UDP buffer and does not set DO. It sets RD=1, asking its resolver to do the recursion on its behalf. The client receives its answer only after the resolver has finished its work. The walkthrough places the remaining traffic, the other 31 frames, on the resolver’s side of the network.
Why the root replies were truncated
The most important event in this trace is the combination of two resolver settings in its upstream queries: a 512-byte EDNS UDP buffer and DO=1. The root’s first two replies came back with TC=1, meaning the answer did not fit in a UDP response at that size. The resolver then repeated those queries over TCP. The walkthrough reports full root answers of 1,109 and 1,179 bytes once they arrived over TCP.
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In this capture, the retry phase accounts for about 56 ms of a 159 ms client query-to-answer lookup. Those numbers describe this one trace. They do not show typical DNS timing, and they do not establish that DNSSEC always causes TCP fallback. Responses of this size can truncate for other reasons, and resolvers differ in the buffer sizes they advertise.
Referrals and glue
Upstream queries in this trace use RD=0, which tells each server not to recurse on the resolver’s behalf. Each parent server returns a referral naming the next zone’s nameservers. Where a nameserver’s name sits inside the zone it serves, the referral also carries glue: the server’s address, so the resolver can reach it without a separate lookup. That is how the resolver moves from the root to .com, then to infoblox.com, and finally receives an authoritative answer with AA=1.
What the DNSSEC signatures do and do not prove
The walkthrough notes that DNSSEC signatures appear in the upstream responses. The trace also has two gaps that matter. It contains no DNSKEY queries, and the client’s response has the AD (Authenticated Data) bit clear.
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So the trace shows DNSSEC-related data being requested and returned. It does not show that the resolver validated the signature chain for this answer. Do not read the presence of RRSIG data as proof of validation. To check validation on your own captures, look for the DNSKEY and DS queries, and for AD=1 in the response to a client that asked for it.
Reading the trace yourself: a short checklist
- Filter by DNS and sort by time to separate the client’s query and reply from resolver-side traffic.
- Check the EDNS OPT record on each upstream query for the advertised UDP size and the DO bit.
- Look for TC=1 replies, then for the same question repeated over TCP.
- Read each referral’s authority and additional sections to find the next zone’s servers and their glue.
- Treat the AD bit and any DNSKEY queries as the evidence for validation, not the presence of signatures alone.
Capture format context
The capture in this article is a PCAPNG file, which keeps transport-level detail: IP headers, TCP streams, and fragmentation. IETF RFC 8618, “Compacted-DNS (C-DNS): A Format for DNS Packet Capture” (September 2019), describes a different goal. C-DNS represents collections of DNS messages more efficiently for storage and transmission, and it can omit data that DNS analysis does not need. The RFC also notes that converting C-DNS 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. Use C-DNS when you want a compact DNS message archive, and PCAP or PCAPNG when you need the full transport picture.
Software options for this kind of annotation
VisualEther is the commercial tool used in the run described above. EventHelix’s product page describes it as downloadable command-line software for Windows, macOS, and Linux, with DNS among its protocol templates. The vendor documents three editions. Check the vendor’s site for current terms before buying.
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| Edition | Intended user | What the vendor page describes |
|---|---|---|
| Community | Individuals working on small captures | Free; generates PDF sequence diagrams |
| Professional | Individual developers | AI analysis and browser-based triage |
| Server | Teams running unattended regression analysis | Server and CI use |
The vendor page also describes a 45-day trial. When comparing editions, weigh budget, capture size and page limits, AI and triage features, number of users, and whether you need server or CI use. The trace in this article is a digital file, so no physical equipment is needed to follow the walkthrough.
The workflow is only as reliable as the review that follows it. Treat generated captions as a first draft, check every field-level claim against the packets, and have someone who knows DNS read the result before it is published.
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