c-ping

c-ping is a very simple and small ping tool that sends ICMP Echo datagram to a host.

ICMP Echo or Echo reply message

The structure of ICMP Echo or Echo reply message:

  0               1               2               3
  0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 8 9 A B C D E F
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |     Type      |     Code      |          Checksum             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |           Identifier          |        Sequence Number        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  	                    Data(Optional)...                    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

1. Type: 8 for echo message, and 0 for echo reply message
2. Code: for echo or echo reply, it should be 0
3. Checksum: 16 bits, it will be computed by the checksum algorithm
4. Identifier: may be used like a port in TCP or UDP to identify a session
5. Sequence Number: may be incremented on each echo request sent

The destination returns the same Identifier and Sequence Number in the reply.

Checksum algorithm

This algorithm based on RFC1071 is below:

1. Set checksum field of request to 0
2. Add each 16 bits from request to sum
3. Add the remaining byte if it’s odd
4. Add the high 16 bits to the low 16 bits util the high 16 bits are 0
5. The complement of sum is the checksum

To check a checksum, just pass the datagram with the checksum to this method, then check if the result is 0

Example

Ensure that you have installed the go environment first, then just run following commands:

# generate c-ping
go build ping.go

# start to ping
./ping  github.com