TransitPacket

How to Investigate a Suspicious IP Address in Your Client's Logs

A fast, three-tool triage process for freelance IT consultants and small MSPs: what a suspicious IP actually is, how to assess it in minutes, and how to talk to the client about it without overreacting.

A client messages you: "I'm seeing a bunch of failed login attempts from some IP address — should I be worried?" Or their firewall dashboard shows a spike in traffic from a country they don't do business in. This is the fast triage process for exactly that message — three tools, in sequence, each answering one specific question, so you can give the client an actual answer instead of a shrug.

Step 1: IP Lookup — where is this actually coming from?

Start with IP Lookup. Enter the IP and look at:

  • Organization / ISP — a familiar cloud provider name (AWS, DigitalOcean, OVH) versus an unfamiliar or blank organization tells you something different about who's likely behind the connection.
  • Country — is it somewhere the client would plausibly have real traffic from, or somewhere they have zero business relationship with?

On its own, this doesn't prove anything — plenty of legitimate traffic comes from cloud providers and unexpected countries. It's the first data point, not the verdict.

Step 2: ASN Lookup — what kind of network is this, really?

Next, run the same IP through ASN Lookup. This is where the real signal usually is, and it's worth understanding the distinction:

  • Residential ISP ASN (a regional broadband provider, a mobile carrier) — a failed login from here is much more likely to be an actual person, possibly even the client themselves mistyping a password, than an automated attack.
  • Hosting or cloud provider ASN (AWS, DigitalOcean, Hetzner, OVH, and similar) — real people don't typically browse to a login page from a datacenter. Repeated login attempts from a hosting-provider ASN is a meaningfully stronger signal of scripted or automated attack activity than the same pattern from a residential IP, precisely because legitimate human traffic doesn't normally originate there.
  • VPN or proxy-associated ASN — doesn't automatically mean malicious on its own (plenty of real, privacy-conscious users route through VPNs), but combined with repeated failed logins, it raises the signal further rather than lowering it.

Step 3: Reverse DNS — does it match what it claims to be?

Finally, run it through Reverse DNS Lookup. This matters most when the traffic is claiming to be something specific — a log entry with a user-agent saying "Googlebot," for instance. Real Googlebot IPs have PTR records that resolve back to Google's own infrastructure; an IP claiming to be Googlebot with no matching reverse DNS (or one pointing somewhere unrelated) is a real red flag for spoofing.

A missing PTR record on its own isn't suspicious — plenty of legitimate IPs don't have one. But combined with the ASN and claimed-identity context from the steps above, it's one more data point feeding the same picture.

What to actually tell the client

Three free tools and a few minutes of triage is a reasonable first pass, not a forensic investigation — be honest about that scope when you report back:

  • Give a plain-language assessment, not a technical dump. "This looks like automated scanning from a hosting provider, not a real customer — low risk right now, but worth blocking" tells the client something they can act on. A list of ASN numbers and PTR records doesn't.
  • Scale your recommendation to the actual signal. A single failed login from a residential ISP probably just needs a "keep an eye on it." Repeated attempts from a hosting-provider ASN with no matching reverse DNS for its claimed identity is worth actually blocking at the firewall or CDN level.
  • Say clearly when it's beyond a quick check. If there's any sign of an actual successful login rather than just attempts, or if the pattern is genuinely large-scale, say so plainly rather than downplaying it because the client would prefer good news.

Bookmark this page — it's built to be the reference you pull up any time a client hands you a suspicious IP and wants a fast, real answer.

FAQ

Does a hosting-provider IP always mean an attack?

No. Legitimate services — uptime monitors, API integrations, some browser extensions, third-party tools the client actually uses — call from datacenter IPs too. Context matters: what's actually being hit, how often, and whether it matches a recognizable attack pattern (like repeated failed logins) rather than a single benign request.

All three tools point to something suspicious — what now?

That's beyond "note it and move on." Recommend blocking the IP or its range at the firewall or CDN level (Cloudflare, if the client has it in front of their site), and if there's any sign of an actual successful login rather than just failed attempts, treat it as a real incident, not just a finding — these three tools are fast triage, not a substitute for a full incident response process.

How does this fit with the other guides?

The DNS Records and Security Headers checklists are proactive — things you check before there's a problem. This one is reactive — what you reach for when a client already has something specific in front of them (a log entry, a firewall alert) and needs an answer fast. All three are deeper references off the fast 10-Minute Network Health Check you'd run at the start of any engagement.