Redo the famous network utility ping with various flags. Skill : Network and System administration
8 bytes header + 56 bytes payload by default.
He is meant to handle errors of IP protocol. Each relay (routers or stations) manage ICMP header by default.
The header will always have a size of 8 bytes. He is encapsulated inside the IP protocol, which means the ICMP header is positionned right after the IP header.
We use the SOCKET_RAW type and the IPPROTO_ICMP protocol when we create the socket, check the man page for more details.
A Raw socket is required since it's a protocol with no user interface (see the Linux raw man page.)
Schema :
_______________________________________________________________
| _________________________________________ ______ |
|________|____|____|____|____|____|____|____|____|__|____|____|
| ^ ^ ^_____^ ^_____^ ^_____^ ^
| | | | | | | | | |
| | | | | | | | | |
(IP) Type Code Checksum ID Seq Number (Data)
Each column represent an octet : 8 octets
Preceded by IP header.For more informations I recommend the website FrameIP for french readers.
Ping is basically use to validate or invalidate the presence of a host on a network.
ping use the ECHO_REQUEST 8/0 and the ECHO_REPLY 0/0 Type and Code.
- If the host receive the message, he will make an
ECHO_REPLY. - If the host has not be found or is unreachable, the last relay will return a ICMP packet to let us know about it.
To identify a packet, we use :
- The ID is filled with the UID.
- The Sequence Number filled with a number incremented at each ECHO_REQUEST sent.
- The TTL (in the IP datagram) set as max value (255) and decremented at each relay point.
The Packet is timed out and returned by the relay if the TTL reach 0. It can be manually set with the option -t.
Payload's data is composed of a timestamp (a stuct timeval, check here), then filled. The user can give an arbitrary packet size with -s or choose a specific timestamp with -T.
Note that the timestamp is not mandatory, the data can be filled with anything.
Ping gives the sum of a send packet each 1scd by default. If the process is interrupted by a SIGINT signal (Ctrl-C), ping will produce a sum-up of the session.
For the rest like the content of the packets' sum or the session sum-up, it depends on the implementation.
To be consistent here with choose to stick with Debian 11 (Bullseye) output, like this example :
~/ft_ping$ ping google.com
PING GOOGLE.com ([HOST_IP]) 56(84) bytes of data.
64 bytes from wr-in-f102.1e100.net ([HOST-IP]): icmp_seq=1 ttl=128 time=18.2 ms
64 bytes from wr-in-f102.1e100.net ([HOST-IP]): icmp_seq=2 ttl=128 time=18.0 ms
64 bytes from wr-in-f102.1e100.net ([HOST-IP]): icmp_seq=3 ttl=128 time=24.2 ms
64 bytes from wr-in-f102.1e100.net ([HOST-IP]): icmp_seq=4 ttl=128 time=24.4 ms
^C
--- GOOGLE.com ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3006ms
rtt min/avg/max/mdev = 17.982/21.184/24.401/3.116 msWhich can be resumed by :
- Header : PING
<dest>(<host>)<ICMP header bytes>(<IP header bytes>) bytes of data. - Packet sum :
<bytes received>bytes from<sender>(<Host IP address>): icmp_seq=<packet number>ttl=<ttl remaining>time=<time enlapsed> - Statistics : little header, then
<total nb>transmitted,<total received>received,<% of loss>packet loss, time<total time enlapsed>- rtt min/avg/max/mdev =
<round trip time>
-I <interface> : let you define a virtual or a physical address interface instead of the default one. The user can use the IP address or the interface name. Trigger a warning if the loopback address is used since it cannot work.
-S <size> : Set the limit of the socket send buffer in bytes. The minimum value is 2048 bytes and it triggeres errors if this is not correctly set, or if a packet is sent with a size that exceed the limit previously set.
-t <value> : Set the TTL value of the IP header. If the option is not provided the TTL is set to the system default, which can vary depending from one distribution to the other (Ex : between Debian or Manjaro / between Debian and Macos).
-T <timestamp> : This is an interesting one. Since the time enlapsed printed by ping as default is the one between a ECHO_REQUEST and a ECHO_REPLY (RTT), this option will make the IP header timestamp be filled with local time then send the ECHO_REQUEST with it ; and the receiver is asked to do the same in return in his ECHO_REPLY packet.
It means that with this option, the user can calculate the time that enlapsed between a sent ECHO_REQUEST (by local machine) and a received ECHO_REQUEST (by the targeted machine), in other words the time a ECHO_REQUEST makes between two hosts and not only the round trip time.
For a better explanation with a Wireshark example, check this video.
This option is not implemented yet.
-M <hint> : Use the MTU discovery path destined to optimize packet sending by avoiding to send fragmented packets. Another article is usefull to give us an example on how it's implemented beyond this program. This option is not implemented yet.
-n : Forbidden the resolution and the use of the Canon Name (see CNAME record). The only change is to not use the flag AI_CANONNAME in the struct addrinfo passed as hint to getaddrinfo() (check the getaddrinfo man).
-w / -W : set respectively a deadline or/and a timeout in second. For the deadline, a fork is used to send a SIGINT signal when the deadline is reached. A minimum and a maximum is set for both.
For more details on socket options, check here.
I.P. : Internet Protocol.
I.C.M.P. : Internet Message Control Protocol.
UID : User Identifier. Retrieved by the C function getuid().
RTT : Round Trip Time.
TTL : Time To Live.