ASN: A Bash-Powered Network Intelligence Swiss Army Knife for Incident Response

Hook

Most network recon tools make you choose between depth and breadth. ASN gives you both—without sending a single packet to your target.

Context

Network incident response traditionally meant juggling a dozen different tools: whois for IP assignments, Team Cymru for ASN lookups, RIPEstat for BGP data, Shodan for port scans, MaxMind for geolocation, and mtr for traceroutes. Each query required remembering different CLI flags, API formats, or web interfaces. When investigating a potential BGP hijack at 3 AM or triaging suspicious IPs from firewall logs, context-switching between these tools burns precious minutes.

ASN emerged from this operational pain point. Rather than building yet another specialized tool, developer nitefood created a bash orchestration layer that queries multiple authoritative sources—Team Cymru, RIPEstat, PeeringDB, Shodan, and others—and synthesizes their responses into coherent intelligence. The result is a single command that answers ‘What is this IP/ASN/prefix?’ with the depth of a security analyst’s workflow, not just a raw database dump. With 1,850 GitHub stars and packaging in Debian, Arch, and FreeBSD repositories, it’s become a widely-adopted OSINT aggregator for teams who need speed without sacrificing comprehensiveness.

Technical Insight

At its core, ASN is an exercise in bash’s underrated strengths: orchestrating external processes, parsing text streams, and formatting terminal output. The script operates in three distinct modes—interactive CLI, HTTP server, and JSON API—all from the same codebase. This architectural choice means you can prototype queries manually, then automate them via API, then expose them to non-technical users via a web interface, without rewriting logic.

The interactive mode demonstrates the tool’s aggregation approach. When you query an ASN, the script appears to fire requests to multiple endpoints including Team Cymru’s DNS-based ASN service, PeeringDB’s API for IXP presence, and RIPEstat for BGP statistics. The README confirms features like organization name, RIR region, IXP presence, global AS rank, BGP statistics (neighbor counts, originated v4/v6 prefix counts), BGP incident history, peering relationships, and announced prefixes.

The RPKI validation feature showcases how ASN adds security context to raw network data. During an AS path trace (using mtr), each hop’s route origin is validated against ROA (Route Origin Authorization) databases. According to the README, this leverages the RIPEStat RPKI validation API and matches each hop’s ASN/Prefix pair with published RPKI ROAs. If origin AS mismatch or unallowed more-specific prefixes are detected, the tool warns of potential route leaks or BGP hijacks along with the offending AS in the path (requires the -d detailed option).

The server mode transforms ASN into a self-hosted traceroute and lookup service. Running the tool with the -l flag starts an HTTP server on a specified port that accepts requests and returns formatted results. The README documents that lookups and traces can be launched from a local or remote browser via bookmarklet or custom search engine, or from terminal via curl, elinks, or similar tools. This enables one-click recon capabilities for security teams.

Shodan integration elevates ASN from passive lookup tool to active recon framework. With a Shodan API key configured, the tool can query Shodan for data about targets (CIDR blocks, URLs, single IPs, or hostnames) and provide breakdowns of open ports, known vulnerabilities, and known software/hardware running on targets—without sending packets to the target. The README confirms support for JSON output, multiple simultaneous targets, and IP list file inputs for Shodan scanning mode. This queries Shodan’s hosted scan data, enabling attack surface profiling without triggering IDS alerts.

Gotcha

ASN’s dependency chain is a notable consideration. The README confirms the tool requires multiple external dependencies including mtr for traceroutes, along with various other utilities. More critically, runtime depends on external API availability: if services like Team Cymru’s DNS service, RIPEstat, or Shodan’s API experience issues, queries may fail or return incomplete data. The tool includes some retry logic and fallback strategies (the README mentions falling back to RIPE’s whois service), but there’s no offline mode for air-gapped investigations.

Bash’s limitations surface during bulk operations. The README documents bulk geolocation capabilities, but processing large numbers of IPs requires sequential API calls that are constrained by rate limits, which can impact performance. For production integrations where guaranteed uptime matters, the dependency on multiple external APIs introduces potential points of failure. The tool is designed for interactive investigation and incident response rather than high-throughput production monitoring.

Verdict

Use ASN if you’re doing incident response, threat hunting, or network investigations where speed and comprehensive context matter. It’s ideal for security teams who need to quickly answer ‘Who owns this IP? What’s their reputation? What routes does traffic take to reach them?’ without assembling answers from multiple separate tools. The Shodan integration is valuable for reconnaissance—querying existing scan data beats sending probes to targets. The self-hosted server mode enables organizations to give analysts and staff lookup capabilities without relying on public traceroute sites. Skip ASN if you need guaranteed uptime for production monitoring (those API dependencies introduce fragility), or offline functionality for air-gapped environments. For small security teams, individual researchers, and incident responders who need rapid network intelligence aggregation, ASN delivers substantial value as an open-source orchestration layer over authoritative network data sources.