ftr - Fast TraceRoute

Multi-Mode Probing in ftr v0.2.1

Overview

Starting with v0.2.1, ftr supports multiple probing modes with automatic fallback. This allows the tool to work in various permission environments and network configurations.

Supported Modes

ICMP Modes

  1. Raw ICMP (Highest privilege)
    • Socket: SOCK_RAW with IPPROTO_ICMP
    • Requires: CAP_NET_RAW capability or root (except Windows)
    • Features: Full control over IP and ICMP headers
    • Platform: Linux, macOS, Windows, FreeBSD, OpenBSD
  2. DGRAM ICMP (Medium privilege)
    • Socket: SOCK_DGRAM with IPPROTO_ICMP
    • Requires: Root or configured ping_group_range (Linux), no root needed (macOS)
    • Features: Kernel handles IP layer
    • Platform: Linux, macOS (NOT supported on FreeBSD/OpenBSD)

UDP Mode

  1. UDP (Platform dependent)
    • Socket: SOCK_DGRAM with IPPROTO_UDP
    • Linux: No privileges required (uses IP_RECVERR)
    • Other platforms: Requires root (needs raw ICMP socket)
    • Features: Traditional UDP traceroute (ports 33434+)
    • Platform: All
    • Note: Linux can receive ICMP errors via IP_RECVERR without root

TCP Mode (Future - v0.3.0)

  1. TCP SYN (Planned)
    • Socket: SOCK_RAW or SOCK_STREAM
    • Features: TCP-based traceroute

Automatic Fallback

The socket factory automatically tries modes in order of capability:

ICMP Raw → ICMP DGRAM → UDP

For example:

Command Line Usage

# Default (automatic mode selection)
ftr google.com

# Force UDP mode
ftr -U google.com

# Force ICMP mode (will fail if insufficient permissions)
ftr -I google.com

# TCP mode (not yet implemented)
ftr -T google.com -p 443

Architecture

Socket Abstraction

All probe modes implement the ProbeSocket trait:

pub trait ProbeSocket: Send + Sync {
    fn mode(&self) -> ProbeMode;
    fn set_ttl(&self, ttl: u8) -> Result<()>;
    fn send_probe(&self, target: IpAddr, probe_info: ProbeInfo) -> Result<()>;
    fn recv_response(&self, timeout: Duration) -> Result<Option<ProbeResponse>>;
    fn destination_reached(&self) -> bool;
}

Factory Pattern

The create_probe_socket function handles mode selection:

let socket = create_probe_socket(
    target_ip,
    Some(ProbeProtocol::Udp)  // Preferred protocol
)?;

Implementation Status

Testing

Run the socket test example:

# Test default mode selection
cargo run --example test_socket -- google.com

# Test UDP mode
cargo run --example test_socket -- google.com --udp

Platform Compatibility Matrix

Platform Raw ICMP DGRAM ICMP UDP (send) UDP (recv ICMP) Non-root Option
Linux Root Root/ping_group No root No root (IP_RECVERR) ✓ UDP or DGRAM
macOS Root No root No root Root ✓ DGRAM ICMP
Windows No admin N/A No admin No admin ✓ Raw ICMP
FreeBSD Root N/A No root Root ✗ None
OpenBSD Root N/A No root Root ✗ None

Privilege Requirements Summary

Privilege requirements vary by mode and platform:

Key insights:

Troubleshooting

“Failed to create any probe socket”

This means none of the modes could get the required privileges. Solutions:

  1. Run with sudo (works for all modes): 
    sudo ftr google.com
  2. Configure ping_group_range (Linux only, enables DGRAM ICMP): 
    echo "net.ipv4.ping_group_range = 0 65535" | sudo tee -a /etc/sysctl.conf
sudo sysctl -p

    After this, DGRAM ICMP mode will work without sudo.

“UDP mode requires root privileges”

UDP traceroute sends UDP packets (no privileges needed) but must receive ICMP “Port Unreachable” responses, which requires a raw socket. There’s no way around this requirement.

Platform-Specific Notes