The Problem You're debugging a connectivity issue. ping works fine, but curl times out. The usual approach: Run traceroute with ICMP - looks fine Run traceroute with TCP - dies at hop 6 Manually compare each hop Finally identify the firewall/ACL What if you could see this in one command? Protocol Divergence Localization I added this feature to multiprobe , a Rust network probing library. It runs ICMP, TCP, and UDP traceroutes simultaneously and identifies where protocols start behaving differently. $ sudo multiprobe divergence problematic-host.example.com
Protocol Divergence Analysis: problematic-host.example.com ( 203.0.113.50 ) Protocols: [ "ICMP" , "TCP" , "UDP" ] Hop ICMP TCP UDP Status --- -------------------- -------------------- -------------------- ---------- 1 192.168.1.1 ( 1.23ms ) 192.168.1.1 ( 1.45ms ) 192.168.1.1 ( 1.12ms ) ✓ 2 10.0.0.1 ( 5.67ms ) 10.0.0.1 ( 5.89ms ) 10.0.0.1 ( 5.34ms ) ✓ 3 172.16.0.1 ( 8.90ms ) * ( timeout ) * ( timeout ) ⚠ DIVERGE
Summary: Protocol divergence detected at hop 3. Path score: 0.33 First divergence at hop 3 Reason: ICMP succeeded, TCP/UDP failed Hop 3 is the culprit. That's 172.16.0.1 - probably a firewall blocking TCP/UDP but allowing ICMP. How It Works Parallel Probing : Send ICMP echo, TCP SYN, and UDP packets with increasing TTL values simultaneously Per-Hop Comparison : At each hop, compare which protocols got responses Divergence Detection : Calculate an "agreement score" (1.0 = all agree, 0.0 = complete disagreement) Report : Identify the first hop where protocols start behaving differently Library Usage use multiprobe ::{ analyze_divergence , DivergenceOptions , DivergenceProtocol }; use std :: time :: Duration ; #[tokio::main] async fn main () -> Result < (), multiprobe :: Error > { let options = DivergenceOptions { max_hops : 30 , timeout_per_hop : Duration :: from_secs ( 2 ), protocols : vec! [ DivergenceProtocol :: Icmp , DivergenceProtocol :: Tcp , DivergenceProtocol :: Udp , ], tcp_port : 80 , udp_port : 33434 , }; let result = analyze_divergence ( "example.com" , & options ) .await ? ; if let Some ( hop ) = result .first_divergence_hop { println! ( "Divergence at hop {}" , hop ); } else { println! ( "No divergence - all protocols behave consistently" ); } Ok (()) } Use Cases Firewall Rule Debugging : Find which hop has a blocking ACL Middlebox Detection : Identify protocol-specific traffic shaping ISP Troubleshooting : Pinpoint where the problem is Network Security Audit : Verify filtering rules are applied where expected Installation # CLI tool cargo install multiprobe # Library cargo add multiprobe Requires elevated privileges (raw sockets) on Linux/macOS. Links: crates.io GitHub Documentation