original.md

Original Socket Coding Back

• write a new higher-level transport protocol based on IP protocol

1. Create original socket

method

int socket(int family, int type, int protocol)

parameters

• family: AF_INET
• type: SOCK_RAW
• protocol:
  • IPPROTO_ICMP: ICMP數據包
  • IPPROTO_IGMP: IGMP數據包
  • IPPROTO_IP: IP數據包

return value

• >=0: success
• -1: failure

2. Set IP options

• set whether automatically fill the IP header

int on = 1;
setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL, &on, sizeof(on));

• on=0: 由協議自動填充
• on=1: 用戶程序填充

3. Bind

• if IP_HDRINCL has been set, bind() takes no effect, and you must fill each IP datagram by yourself
• local bind: bind()
• opposite bind: connect()

4. Send or Receive

send

• if you has not called connect() to bind, you must use sento() or sendmsg() to send data
• if you has called, then write() or send() is allowed to use

receive

• data from UDP and TCP won't be sent to original socket
• receive data from ICMP
  • echo response
  • timestamp response
  • mask response
  • ...
• receive data from other types of protocols
• receive data which cannot be recognized by the Kernel