lumenthi / ping

GNU ping implementation

GNU Linux ping implementation

Send ICMP ECHO_REQUEST to network hosts

Description

General

• Ping works by sending a ICMP echo request packet to a target host and waiting for the ICMP echo reply
• The Internet Control Message Protocol (ICMP) is a network layer protocol used by network devices to diagnose network communication issues

Properties

• Internet Control Message Protocol (ICMP) is a stand-alone protocol
• ICMP is not associated with any transport layer protocol, such as Transmission Control Protocol (TCP) or User Datagram Protocol (UDP).
• It is a connectionless protocol, meaning a device does not need to open a connection with the target device before sending a message.
• ICMP packets are described within this structure

struct s_packet
{
  struct icmphdr hdr {
      u_int8_t type;            /* Message type (echo, echo reply, etc...) */
      u_int8_t code;            /* Error codes (Host unreachable, TTL exceeded...) */
      u_int16_t checksum;       /* 16-bit one's complement of the one's complement sum of the ICMP message */
      u_int16_t echo.id;        /* PID of the program */
      u_int16_t echo.sequence;  /* Sequence number, is incremented by 1 for each packet */
      u_int32_t gateway;        /* Used for ICMP redirect type */
      [...]                     /* Unused */
  }
  char *msg;
}

Transport

• ICMP packets are encapsulated in IP packets, it relies on IP to transmit its messages.
• Internet Protocol (IP) is a protocol for connectionless services.

Implementation

Socket

• A user protocol may receive ICMP packets for all local sockets by opening a raw socket with the protocol IPPROTO_ICMP

socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)

Resolve

• Convert domain names, hostnames, and IP addresses to structured binary formats for the operating system's networking API

getaddrinfo(host, NULL, &hints, &res)

• Convert IPv4 and IPv6 addresses from binary to text form

inet_ntop(AF_INET, &((const struct sockaddr_in *)ret->ai_addr)->sin_addr, g_data.ipv4, sizeof(g_data.ipv4))

IP options

• Since ICMP packets are encapsulated in IP packets, we use IPROTO_IP in the socket option, by doing this the kernel will manage the IP header by himself.
• TTL option

setsockopt(g_data.sockfd, IPPROTO_IP, IP_TTL, &g_data.ttl, sizeof(g_data.ttl))

• Timeout option

setsockopt(g_data.sockfd, SOL_SOCKET, SO_RCVTIMEO, (const char*)&timeout, sizeof(timeout))

Send and receive loop

• Wait time is handled with SIG_ALRM, a signal is raised every X sec. (subject's constraint)

signal(SIGALRM, alarmhandler);

• Format packet

ft_memset(&packet, 0, sizeof(packet));
packet.hdr.type = ICMP_ECHO;
packet.hdr.un.echo.id = getpid();
packet.hdr.un.echo.sequence = g_data.seq++;
packet.hdr.checksum = checksum(&packet, sizeof(packet));

• Send packet

sendto(g_data.sockfd, &packet, sizeof(packet), 0, g_data.host_addr, sizeof(*(g_data.host_addr))

• Wait for reply

recvmsg(g_data.sockfd, &msg, 0)

• Check validity of the packet

if (ret.hdr.type == ICMP_ECHOREPLY)

• Print the packet

print_packet(ret, g_data.seq, start_time);

End of the loop (CTRL-C pressed or -c option specified)

• Print summary

print_end();

• Free host infos

freeaddrinfo(g_data.host_info);

Options

Implemented options:

-c <count>      stop after <count> replies.
-f              flood ping.
-h              print help and exit.
-i <interval>   seconds between sending each packet.
-q              quiet output.
-t <ttl>        set time to live.
-v              verbose output.
RTT             round trip time, min, max, average.

Make

Given Makefile contains all standard rules

• all
• clean
• fclean
• re

Example output

$ make
 ~ | Compiled libft
 ~ | Compiled ft_ping
$ sudo ./ft_ping localhost     
PING localhost (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.013 ms
64 bytes from localhost (127.0.0.1): icmp_seq=2 ttl=64 time=0.034 ms
64 bytes from localhost (127.0.0.1): icmp_seq=3 ttl=64 time=0.021 ms
64 bytes from localhost (127.0.0.1): icmp_seq=4 ttl=64 time=0.021 ms
64 bytes from localhost (127.0.0.1): icmp_seq=5 ttl=64 time=0.021 ms
^C
--- localhost ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4411ms
rtt min/avg/max = 0.013/0.022/0.034 ms