README

Tiny ICMP Ping (C, Linux/WSL)

• TLDR:

A minimal ping-like tool that crafts ICMP Echo requests and receives Echo replies.
It supports RAW and ICMP DGRAM sockets, hex dumps, simple RTT stats, and WSL-friendly options.

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feat: implement tiny ICMP ping tool with RAW/DGRAM support, RTT stats, and WSL fixes

• Add ICMP Echo builder + checksum
• Support RAW socket send/recv (parse IP header)
• Support ICMP DGRAM recv with TTL via recvmsg(IP_RECVTTL)
• Implement CLI flags (-c, -i, -W, -t, -s, -v, -A, -M)
• Add auto-fallback from DGRAM to RAW on EPERM/EACCES
• Hex dump for first packet, RTT stats summary
• WSL-specific adjustments: -A to ignore id, ping_group_range note

This MR adds a minimal ICMP ping utility in C with support for RAW and ICMP DGRAM sockets.
Includes checksum, RTT stats, hex dump, CLI args, auto-fallback, and WSL notes.
Verified against 1.1.1.1, 8.8.8.8, and localhost on WSL2 with tcpdump confirmation.

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Files

ping_like_c/
├── ping.c // main program (ICMP echo build/send/recv, CLI)
├── ping.h // small header with types and helpers
└── Makefile // build rules (links with -lm)

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Build

make

or explicitly:

cc -O2 -Wall -Wextra -std=c2x -D_POSIX_C_SOURCE=200809L -c ping.c
cc -O2 -Wall -Wextra -std=c2x -D_POSIX_C_SOURCE=200809L -o ping ping.o -lm

We link with -lm because RTT stats use sqrt().

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Usage

./ping [-c count] [-i ms] [-W ms] [-t ttl] [-A] [-v] [-M auto|raw|dgram] [-s size] host

  -c N      number of packets (default 4)  
  -i MS     interval between sends in ms (default 1000)  
  -W MS     per-packet timeout in ms (default 5000)  
  -t N      set IP TTL/hop limit  
  -A        loose match: ignore ICMP identifier (id)  
  -v        verbose: log ICMP seen (replies/errors)  
  -M MODE   socket mode:  
              auto  → try dgram, if denied fall back to raw (default)  
              raw   → raw socket (IP header included in recv path)  
              dgram → datagram ICMP (no IP header in payload)  
  -s SIZE   payload size in bytes (default 56; fills 'A'..'Z' pattern)  

Examples

Plain ping with hex dump, raw fallback if needed

./ping 1.1.1.1

10 packets, 500 ms interval, 7 s timeout

./ping -c 10 -i 500 -W 7000 8.8.8.8

Verbose + DGRAM (works great on WSL after enabling permission)

./ping -M dgram -v -c 3 cloudflare.com

If you see replies but “timeout” lines, add -A (ignore id rewrite)

./ping -M dgram -A -v -c 3 8.8.8.8

What’s implemented

• ICMP Echo builder with 16-bit 1’s complement checksum.
• RAW socket send/recv path (parses IP header + ICMP).
• ICMP DGRAM socket recv path (no IP header), with TTL via recvmsg + IP_RECVTTL.
• Auto-fallback: -M auto (default) tries DGRAM, on EPERM/EACCES it falls back to RAW and prints a short note.
• Options: -c, -i, -W, -t, -s, -v, -A, -M.
• Debug: one-time hex dump of the first packet.
• Stats: min/avg/max/mdev RTT summary.

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WSL notes

WSL2 + Hyper-V NAT can behave differently for ICMP:

• With RAW sockets, some targets (e.g., 1.1.1.1) work; others (e.g., 8.8.8.8) may show no replies arriving.
• ICMP DGRAM is often more reliable on WSL, but the kernel can rewrite the ICMP identifier (id).
  Our tool offers -A to ignore id and match on sequence (this made 8.8.8.8 and localhost work for you).
• To allow ICMP DGRAM for unprivileged users, enable:
  sudo sysctl -w net.ipv4.ping_group_range="0 2147483647"

  persist:

  echo 'net.ipv4.ping_group_range=0 2147483647' | sudo tee -a /etc/sysctl.conf sudo sysctl -p
• Alternative: grant the binary capability so you don’t need sudo:
  sudo setcap cap_net_raw+ep ./ping

Troubleshooting flow

1. If RAW mode times out for a host but system ping works, try:
   ./ping -M dgram -A -v -c 3 <host>
2. If you get “Permission denied” in DGRAM:
   • enable ping_group_range (above), or
   • run sudo setcap cap_net_raw+ep ./ping, or run as root.
3. Use tcpdump to confirm whether replies reach the WSL interface:
   sudo tcpdump -ni any icmp and host 8.8.8.8

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Known quirks so far

• Loopback (127.0.0.1):
  On some WSL/kernel combos, RAW shows only your own Echo Requests (type 8).
  DGRAM receives real Echo Replies, but id may be kernel-managed. Use -A.
• TTL in DGRAM:
  We fetch TTL via IP_RECVTTL; if unsupported, TTL prints as -1.

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Security / permissions

• RAW and DGRAM ICMP can require special privileges.
  We support three ways to run:
  • sudo ./ping ...
  • sudo setcap cap_net_raw+ep ./ping → then run as normal user
  • widen ping_group_range for DGRAM sockets

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Development trail

• Fixed htons/ntohs warnings by including proper headers.
• Implemented checksum + ICMP Echo header builder.
• Added hex dump, then RTT measurement & summary stats (sqrt() ⇒ -lm).
• Added CLI flags -c, -i, -W, -t, -s, -v, -A.
• Built recv path that checks type=0, id, seq (and -A to relax id).
• Implemented DGRAM mode with TTL via recvmsg(IP_RECVTTL).
• Added auto-fallback from DGRAM to RAW on EPERM/EACCES.
• Verified on WSL:
  • RAW works for 1.1.1.1;
  • DGRAM works for 127.0.0.1 and 8.8.8.8 with -A;
  • tcpdump used to validate traffic.

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Example sessions

$ ./ping -M dgram -A -v -c 3 127.0.0.1
... [dbg dgm] ... ttl=64
64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.20 ms
...

$ ./ping -M dgram -A -v -c 3 8.8.8.8
... [dbg dgm] ... ttl=118
64 bytes from 8.8.8.8: icmp_seq=1 ttl=118 time=25.48 ms
...

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