When troubleshooting DNS resolution issues, dig +trace is often considered the gold standard for identifying authoritative answers. This command initiates a simulated recursive query starting from the root servers, working its way down the DNS hierarchy. Here's what happens under the hood:

$ dig +trace example.com

; <<>> DiG 9.16.1 <<>> +trace example.com
;; global options: +cmd
.                       518400  IN      NS      a.root-servers.net.
.                       518400  IN      NS      b.root-servers.net.
;; Received 525 bytes from 192.168.1.1#53(192.168.1.1) in 4 ms

While many assume +trace completely bypasses local resolvers after root server contact, the reality is more nuanced. The command does use your configured resolver for:

• Initial root server list resolution
• Potential fallback lookups when intermediate NS records lack glue
• Final authoritative query validation

To test resolver involvement, you can combine +trace with packet capture:

$ sudo tcpdump -i eth0 -nn port 53 & dig +trace example.com > /dev/null

This reveals whether queries are being sent to your local resolver versus directly to authoritative nameservers.

Several scenarios can affect +trace accuracy:

# When glue records are missing:
$ dig +trace +additional broken.example.com

# When TTLs are mismatched:
$ dig +trace +ttl example.com

# With DNSSEC validation:
$ dig +trace +dnssec secured-domain.org

For complete independence from local resolvers:

# Direct root server queries
$ dig @a.root-servers.net example.com NS
$ dig @g.gtld-servers.net example.com

Some organizations maintain their own root hints file to avoid any resolver dependency:

$ dig +trace +root=/etc/bind/root.hints example.com

1. Always combine +trace with +additional to view glue records
2. Compare results across multiple root servers
3. Use packet capture when troubleshooting critical issues
4. Consider maintaining local root hints for sensitive environments

When troubleshooting DNS issues, many engineers rely on dig +trace as their go-to tool for authoritative answers. The command's operation appears straightforward:

dig example.com +trace +additional
; <<>> DiG 9.16.1 <<>> example.com +trace +additional
;; global options: +cmd
.                       518400  IN      NS      a.root-servers.net.
.                       518400  IN      NS      b.root-servers.net.
;; Received 525 bytes from 8.8.8.8#53(8.8.8.8) in 12 ms

Contrary to popular belief, dig +trace doesn't operate in complete isolation:

1. Initial root server list comes from local configuration (/etc/bind/named.root or similar)
2. For each nameserver encountered beyond roots, dig performs A/AAAA lookups
3. These lookups typically use your configured resolver unless explicitly overridden

You can demonstrate this behavior with packet captures:

tcpdump -n -i any port 53 & 
dig +trace example.com

The output will show queries to your local resolver for intermediate NS records.

For truly authoritative traces without local resolver interference:

# Using known root server IPs directly
dig @198.41.0.4 example.com +trace +norecurse

# With DNSSEC validation
delv example.com +trace

Where dig +trace might lead you astray:

• Combine with +norecurse to prevent fallback to resolver
• Use +bufsize=4096 to handle large responses
• Verify against multiple root servers (a-m.root-servers.net)
• Cross-check with drill or kdig alternative tools