How to Install and Use tcproute for Reliable Path Discovery

How to Install and Use tcproute for Reliable Path Discoverytcproute is a traceroute-like utility that sends TCP SYN packets (rather than UDP or ICMP) to probe each hop along a network path. Because many modern networks and firewalls prioritize or allow TCP traffic (often on common ports like 80 or 443), tcproute can reveal paths that traditional traceroute tools miss. This article explains what tcproute does, how it differs from other traceroute tools, how to install it on major platforms, practical usage examples, interpretation of results, advanced options and troubleshooting, and security/ethical considerations.

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What tcproute Does and Why It’s Useful

tcproute discovers the path packets take to reach a target host by sending TCP SYN packets with incrementally increasing TTL (Time To Live) values. Each intermediate router that decrements the TTL to zero replies with an ICMP Time Exceeded message, allowing tcproute to identify the hop. When the packet reaches the destination (or a firewall that accepts the TCP probe), you receive a TCP response (SYN/ACK or RST), indicating path completion.

Why use tcproute?

• Works through firewalls that block ICMP/UDP probes: Many network devices drop traditional traceroute probes, while allowing TCP traffic to specific ports.
• Mimics real application traffic: Probing TCP ports used by real services (HTTP/HTTPS) gives a realistic view of the path that application traffic takes.
• Useful for troubleshooting connection problems: If traceroute shows incomplete paths but tcproute succeeds, the issue may be specific to ICMP/UDP handling.

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Differences: tcproute vs traceroute vs tcptraceroute

• traceroute (classic) usually uses UDP or ICMP Echo with increasing TTL.
• tcptraceroute (a separate tool) and tcproute both use TCP probes; naming varies by distribution. Functionally, tcproute focuses on TCP SYN probes.
• Some systems include a tcptraceroute implementation with different options; check your package names.

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Installing tcproute

Note: Different operating systems and distributions might package tcproute under different names (tcproute, tcptraceroute, or tcp-traceroute). If the specific package isn’t available, consider building from source or using tcptraceroute.

Debian/Ubuntu

1. Update package lists:

   
   sudo apt update 

2. Install tcptraceroute (often available as tcptraceroute):

   
   sudo apt install tcptraceroute 

   If a package named tcproute is unavailable, this provides similar functionality.

Fedora/CentOS/RHEL

On Fedora:

sudo dnf install tcptraceroute 

On CentOS/RHEL, enable EPEL and then:

sudo yum install epel-release sudo yum install tcptraceroute 

macOS

• Using Homebrew:

  
  brew install tcptraceroute 

  If tcproute is not in Homebrew, you can build tcptraceroute from source.

Building from source

1. Install build dependencies (example for Debian/Ubuntu):

   
   sudo apt install build-essential libpcap-dev 

2. Download source (example):

   
   wget https://example.org/tcproute-X.Y.tar.gz tar xzf tcproute-X.Y.tar.gz cd tcproute-X.Y ./configure make sudo make install 

   (Replace URL and version with the actual source location. Many modern systems already include tcptraceroute packages.)

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Basic Usage

Run tcproute with root privileges (required to send raw packets) or with capabilities set (Linux: CAP_NET_RAW). Basic syntax:

sudo tcptraceroute target [port] 

Examples:

• Probe tcp port 80 on example.com:

  
  sudo tcptraceroute example.com 80 

• Probe port 443 (HTTPS):

  
  sudo tcptraceroute 93.184.216.34 443 

Interpreting output:

• Each line corresponds to a hop showing the router IP (and optionally hostname) and the round-trip time(s).
• Final hop may show a TCP response like “S 93.184.216.34:443 (syn-ack)” indicating the destination replied.

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Common Options and Examples

Options vary by implementation. Typical flags include:

• -n : Do not resolve hostnames (faster, shows numeric IPs).
• -p : Specify destination port.
• -m : Set maximum TTL (max hops).
• -q : Number of probes per hop.
• -w : Timeout per probe.

Examples:

• Numeric only, max 30 hops, 3 probes per hop, port 443:

  
  sudo tcptraceroute -n -m 30 -q 3 example.com 443 

• Short timeout 1 second:

  
  sudo tcptraceroute -w 1 example.com 80 

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Interpreting Results — Practical Notes

• If intermediate hops show asterisks (*) or “no reply”, that hop is not returning ICMP Time Exceeded messages. Downstream hops may still respond.
• If tcproute completes where traceroute failed, the path is reachable for TCP on the probed port but ICMP/UDP may be filtered.
• If tcproute stops at a firewall that blocks TCP probes, you may see consistent non-responses starting at the firewall’s IP.
• Varying RTTs between hops are normal; high latency at a single hop isn’t always the bottleneck because routers may de-prioritize ICMP responses.

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Advanced Techniques

• Probe different ports: Use ports 80, 443, 22, or other service ports to see which path the actual service traffic takes.
• Combine with packet captures: Run tcpdump/wireshark to capture the probes and replies for deeper analysis.
• Use asymmetric path detection: Compare tcproute results from both endpoints (if you have access) to detect asymmetric routing.
• Automate and log results: Script periodic tcproute checks to detect routing changes over time.

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Troubleshooting

• Permission errors: Run as root or give binary CAP_NET_RAW:

  
  sudo setcap cap_net_raw+ep $(which tcptraceroute) 

• Package not found: Try tcptraceroute package or build from source.
• Incomplete output: Increase timeout, or try different destination ports.
• Name resolution slow: Use -n to skip DNS lookups.

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Security and Ethical Considerations

• Probing remote hosts can trigger IDS/IPS alerts. Use tcproute only on networks/hosts you own or have permission to test.
• Excessive automated probing can cause performance issues; rate-limit probes.
• Respect terms of service and legal restrictions in your jurisdiction.

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Example Workflow

1. Check basic TCP reachability:

   
   sudo tcptraceroute example.com 443 

2. If blocked, try other common ports:

   
   sudo tcptraceroute example.com 80 sudo tcptraceroute example.com 22 

3. Capture packets while probing:

   
   sudo tcpdump -i any host example.com and tcp and port 443 -w capture.pcap 

4. Compare with ICMP traceroute:

   
   traceroute -n example.com 

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Conclusion

tcproute is a practical tool for discovering network paths using TCP SYN probes, often succeeding where traditional traceroute tools fail due to ICMP/UDP filtering. Use it with appropriate privileges, probe sensible ports, and combine results with packet captures and other diagnostics for the most reliable path discovery.