Linux Networks

1
Linux Networks

• TCP/IP Networking Layers
• BSD Socket Interface
• INET Socket Layer
• Create
• Bind
• Listen
• Accept
• Connect

2
Network Applications
User
Kernel
BSD Sockets
Socket Interface
INET Sockets
TCP
UDP
Protocol Layers
IP
ARP
Network Devices
PPP
SLIP
Ethernet
Linux Networking Layers
3
files_struct
count close_on_exec open_fs fd0 fd1 fd255
BSD Socket File Operations
file
f_mode f_pos f_flags f_count f_owner f_op f_inode
f_version
lseek read write select ioctl close fasync
inode
socket
SOCK_STREAM
type protocol data
Address Family socket operations
SOCK_STREAM
sock
type protocol socket
Linux BSD Socket Data Structure
4
System Call

• ltnet/socket.cgt
• int sys_socketcall(int call,
  unsigned long args)
• call
• ltlinux/net.hgt
• SYS_SOCKET --gt socket()
• SYS_BIND --gt bind()
• ... ...
• args
• args

5
family

• ltinclude/linux/socket.hgt
• AF_UNIX
• Unix domain sockets
• AF_INET
• Internet IP Protocol
• AF_IPX
• Novell IPX
• AF_APPLETALK
• Appletalk DDP
• AF_X25
• Reserved for X.25 project
• ... ...

6
type

• ltinclude/linux/socket.hgt
• SOCK_STREAM
• stream (connection) socket
• SOCK_DGRAM
• datagram (conn.less) socket
• SOCK_RAW
• raw socket
• SOCK_RDM
• reliably-delivered message
• SOCK_SEQPACKET
• sequential packet socket
• ... ...

7
protocol

• ltinclude/linux/in.hgt
• IPPROTO_IP
• Dummy protocol for TCP
• IPPROTO_ICMP
• Internet Control Message Protocol
• IPPROTO_IGMP
• Internet Group Management Protocol
• IPPROTO_TCP
• Transmission Control Protocol
• IPPROTO_EGP
• Exterior Gateway Protocol
• ... ...

8
socket(family, type, protocol)

• ltnet/socket.cgt
• sys_socket(...)
• get an empty inode for socket structure
• allocate a sock structure
• return the file descriptor of the socket if
  success

9
bind(fd, uaddr, addrlen)

• ltnet/socket.cgt
• sys_bind(...)
• bind a name to a socket
• move the socket address to kernel space
• address port checking

10
listen(fd, backlog)

• ltnet/socket.cgt
• sys_listen(...)
• allow the protocol to do anything necessary
• move a socket into listening state

11
accept(fd, sockaddr, skaddrlen)

• ltnet/socket.cgt
• sys_accept(...)
• attempt to create a new socket
• set up the link with the client
• wake up the client
• return the new fd

12
connect(fd, uaddr, addrlen)

• ltnet/socket.cgt
• sys_connect(...)
• attempt to connect to a socket with the server
  address
• move the address to kernel space