Verifying Bingbot with Reverse DNS

Bingbot is impersonated almost as often as Googlebot, and counting spoofed hits corrupts your Bing crawl statistics just as badly. The verification is the same forward-confirmed reverse DNS test, but against Microsoft's crawler domain rather than Google's — with one Bing-specific twist worth knowing. This page is the Bingbot counterpart to verifying Googlebot with reverse DNS, within the identifying search engine bots guide.

Diagnosis: Count the Bingbot Claims

Start by counting how much of your traffic claims to be Bingbot, and from how many distinct IPs:

grep -i 'bingbot' access.log | awk '{print $1}' | sort -u | wc -l
grep -ic 'bingbot' access.log

Expected Output: the count of distinct IPs and total hits claiming Bingbot. A surprising number of unique IPs — especially from consumer networks — is the sign that spoofs are inflating the figure.

Concept: Forward-Confirmed Reverse DNS, Bing Edition

The test resolves the IP to a hostname (reverse DNS), checks the hostname is in Microsoft's official crawler domain, then resolves that hostname back to the original IP (forward confirmation). Verified Bingbot resolves into search.msn.com. The forward-confirm step is what defeats an attacker who controls reverse DNS for their own IP: they cannot make a search.msn.com hostname resolve back to their address. Microsoft also publishes a "Verify Bingbot" tool and a downloadable IP list, giving you a second, authoritative check.

Step-by-Step Fix

Step 1: Reverse-resolve a claimed Bingbot IP.

host 157.55.39.1

Expected Output:

1.39.55.157.in-addr.arpa domain name pointer msnbot-157-55-39-1.search.msn.com.

The pointer must end in search.msn.com. A pointer to any other domain is an immediate fail.

Step 2: Forward-confirm the hostname. Resolve the returned hostname back and confirm it matches the original IP.

host msnbot-157-55-39-1.search.msn.com

Expected Output:

msnbot-157-55-39-1.search.msn.com has address 157.55.39.1

If both halves agree and the domain is search.msn.com, the hit is verified Bingbot.

Step 3: Batch-verify and split the log. Run forward-confirmed reverse DNS across all claimed Bingbot IPs.

awk '/bingbot/ {print $1}' access.log | sort -u | while read ip; do
  ptr=$(host "$ip" | awk '/pointer/ {print $NF}' | sed 's/\.$//')
  if [[ "$ptr" == *search.msn.com ]]; then
    fwd=$(host "$ptr" | awk '/has address/ {print $NF}')
    [[ "$fwd" == "$ip" ]] && echo "$ip VERIFIED" || echo "$ip FAKE"
  else
    echo "$ip FAKE"
  fi
done

Expected Output:

157.55.39.1 VERIFIED
45.132.x.x FAKE

Production Warning: De-duplicate IPs with sort -u before the loop — each unique IP triggers DNS queries, and a busy log can generate thousands, tripping resolver rate limits. Cache results across runs, exactly as the Googlebot verification advises.

Edge-Case Handling

  • Legacy msnbot user-agent. Older Bing crawlers and some services use msnbot rather than bingbot; verified ones still resolve into search.msn.com, so include both tokens in the initial filter.
  • AdIdxBot and BingPreview. Microsoft runs other agents that also resolve into search.msn.com. They are legitimate Microsoft crawlers; treat them by the same domain test, then segment by user-agent if you want Bingbot alone.

Verification

Confirm your split is clean: no verified IP should be outside Microsoft's published ranges, and no fake should resolve into search.msn.com:

grep VERIFIED bing_ip_status.txt | wc -l
grep FAKE bing_ip_status.txt | wc -l

Expected Output: two counts whose sum equals your distinct Bingbot-claiming IPs. Feed only the VERIFIED set into any Bing crawl metric.

Why Bing Verification Matters as Much as Google

It is easy to treat Bing as an afterthought and skip verifying its crawler, but that is a mistake for two reasons. First, Bing powers more search traffic than its market-share headline suggests — it is the engine behind other search products and a meaningful share of enterprise and regional search — so Bingbot's crawl of your site translates into real visibility you do not want to misjudge. Second, and more practically, Bingbot is impersonated just as readily as Googlebot, so any crawl-budget or bot analysis that counts unverified Bingbot traffic is contaminated by the same spoofing problem, and drawing conclusions from that contaminated data leads to wrong decisions about both engines.

The consequence of skipping Bing verification is that your bot analysis is only half-trustworthy. If you verify Googlebot rigorously but count raw Bingbot hits, your total crawler picture mixes verified and unverified data, and any metric that combines them — total crawl rate, share of budget on errors, crawl coverage — inherits the spoofing noise from the Bing side. Applying the same forward-confirmed reverse DNS discipline to Bingbot as to Googlebot is what makes your crawler analysis uniformly trustworthy, so that conclusions drawn from it hold for both engines rather than being clean for one and muddy for the other. Bing verification is not optional polish; it is what completes the verified-crawler dataset that every downstream crawl metric depends on.

Combining the Range List and Reverse DNS

Microsoft, like Google, publishes the IP ranges its crawler uses, which gives you a faster first-pass check to pair with the authoritative reverse-DNS test. The range list lets you classify the bulk of Bingbot-claiming traffic instantly by membership — an IP inside a published Bing range is almost certainly genuine, and one outside every range claiming to be Bingbot is a spoof — reserving the more expensive DNS round-trip for the cases the ranges do not settle. This two-tier approach gives you both the speed of a local lookup and the certainty of forward-confirmed DNS.

# Fast first pass: is the claimed-Bingbot IP in a published Microsoft range?
# (fall back to forward-confirmed reverse DNS for anything the ranges don't settle)
ip=157.55.39.1
grepcidr -f bing_ranges.txt <(echo "$ip") && echo "in published range" \
  || echo "$ip not in Bing ranges — verify by reverse DNS or treat as fake"

Expected Output: an instant classification for IPs the range list covers, and a fallback to reverse DNS only for the ambiguous remainder — the same layered approach that keeps verification fast at scale. The range list and reverse DNS agree on genuine Bingbot, so using the list as the cheap first filter and DNS as the ground-truth confirmation gives you the best of both: minimal DNS traffic on a busy log, and full certainty where it matters. Keep the range list fresh, since Microsoft updates it, and treat a range miss as a prompt to verify rather than an automatic block, because a legitimate crawler IP could appear before the published list catches up.

Building a Verified-Bingbot Dataset for Analysis

Verification is not an end in itself — it exists to produce a clean, verified-Bingbot subset of your logs that every Bing-specific crawl metric can safely use. Once you have run forward-confirmed reverse DNS (or the range check) across the claimed-Bingbot IPs and split verified from fake, persist that verdict so downstream analysis filters to verified traffic without re-verifying. The result is a Bing crawl dataset you can trust: crawl rate, status distribution, section coverage, and budget-waste metrics computed on verified Bingbot alone, uncontaminated by the spoofs that would otherwise inflate every number.

This verified subset is what makes Bing-specific crawl-budget work meaningful. With it, you can compare how Bingbot and Googlebot crawl your site differently — they often prioritize different sections and tolerate different site structures — and tune for each where it matters. Without it, any Bing metric is a blend of real crawler behavior and scraper noise, and the differences you observe might be artifacts of spoofing rather than real engine behavior. Caching the verification verdicts and filtering to the verified set before computing any Bing metric is the same discipline the broader bot-identification work applies to Googlebot, extended to give Bing the same analytical rigor. The payoff is a two-engine crawl analysis where both halves are equally trustworthy, so decisions about site structure, crawl steering, and budget allocation rest on verified data for every crawler that matters.

Applying the Same Rigor to Every Crawler That Matters

The method this page applies to Bingbot generalizes to any crawler whose traffic feeds a decision, and recognizing that generality is what turns a Bing-specific technique into a complete verification practice. Every search and AI crawler that matters to you is impersonated, so every one whose counts inform a decision deserves the same forward-confirmed reverse DNS or published-range verification. The domains differ — Google's crawler resolves into its own domains, Bing's into search.msn.com, and each has its own published ranges — but the method is identical, and applying it uniformly across every crawler is what makes your whole bot dataset trustworthy rather than clean for one crawler and contaminated for the rest.

This uniform rigor matters because analyses often combine crawlers. A total-crawl metric, a comparison of how different engines crawl your site, an assessment of overall bot load — each mixes traffic from multiple crawlers, and the mixture is only trustworthy if every component was verified. Verifying Googlebot carefully while counting raw Bingbot, or verifying both search crawlers while counting raw AI-crawler traffic, leaves the combined numbers contaminated by whichever crawlers you did not verify. Building a verification step for every crawler whose traffic you act on — the same forward-confirmed check against each crawler's own domain and ranges — is what produces a uniformly clean bot dataset, and it is the natural extension of the Bing verification here to the full set of crawlers a mature crawl analysis has to account for.

Verification as the Basis of Trust

The reason Bingbot verification matters comes down to trust: every Bing crawl metric you compute is only as trustworthy as the verification behind the traffic it counts. An unverified Bingbot count is a mix of real crawler activity and scraper noise, and any decision made on that mixed number rests on contaminated data. Verification is what removes the contamination, leaving a clean verified-Bingbot dataset that every metric can safely use. This is why the modest effort of forward-confirmed reverse DNS, cached and reused, is worth building into your Bing analysis — it is the step that converts a suspect number into a trustworthy one, and trustworthy numbers are the only kind worth acting on. Making verification the foundation of your Bing crawl analysis is what lets you treat its conclusions with the same confidence as your Google ones.

Common Mistakes

  • Checking the wrong domain. Bingbot resolves into search.msn.com, not a bing.com or microsoft.com host. Match the correct crawler domain.
  • Skipping forward confirmation. Reverse DNS alone is forgeable by whoever controls the IP's PTR record. The forward-confirm step is what makes it trustworthy.

Frequently Asked Questions

Is Bingbot verification different from Googlebot verification?
The method is identical — forward-confirmed reverse DNS — only the crawler domain differs: search.msn.com for Bing versus googlebot.com/google.com for Google. Microsoft additionally offers a "Verify Bingbot" tool and a published IP list as a second authoritative check, which Google mirrors with its own published ranges.

Why do so many IPs fake Bingbot?
Scrapers impersonate reputable crawlers to evade rate limits and blocks, betting that operators allowlist search bots. Bing is a common disguise for the same reason as Google. Only forward-confirmed reverse DNS — or a match against Microsoft's published IP list — reliably separates the real crawler from the impostors.

Part of the Identifying Search Engine Bots guide.