Network Implementation

Transcription

1 CS 256/456: Operating Systems Network Implementation John Criswell! University of Rochester 1

2 Networking Overview 2

3 Networking Layers Application Layer Format of Application Data Transport Layer Which application? Network Layer Which machine on the Internet? Link Layer Which machine on the local network? 3

4 Networking Layers Application Layer HTTP Transport Layer TCP Network Layer IPv4 Link Layer Ethernet 4

5 Packets Data divided into packets to send across network Data LOLCats! 5

6 Packets Data divided into packets to send across network HTTP Header Data Response-header: LOLCats! 5

7 Packets Data divided into packets to send across network TCP Header Port 23 HTTP Header Data Response-header: LOLCats! 5

8 Packets Data divided into packets to send across network IP Header TCP Header HTTP Header Data Port 23 Response-header: LOLCats! 5

9 Packets Data divided into packets to send across network Ethernet Header IP Header TCP Header HTTP Header Data MAC 00:23:56:00:10: Port 23 Response-header: LOLCats! 5

10 Types of Network Protocols Connection or No connections! Connections: Indicate one time who you are talking to! No connections: Each message specifies recipient! Message boundaries vs. Streams! Reliable vs. Unreliable! Reliable: Will retransmit lost data transparently! Unreliable: Sent data can be lost 6

11 Two APIs to Rule Them All 7

12 System V STREAMS Used in most commercial Unix variants (e.g., Solaris)! More or less discontinued! Implementation has same principles of sockets 8

13 Berkeley Sockets The standard interface for network applications! Linux, FreeBSD, Mac OS X, AIX! Emulated in Solaris and other System V Unices 9

14 Berkeley Sockets Implementation 10

15 Socket: A Pipe for the Network Local! End The Network Remote! End Full-duplex: data moves each direction! Created by socket() system call! Kernel performs all protocol processing 11

16 Socket Socket is a file descriptor! Can (usually) be used like a file Process File Descriptor Table fd fd fd fd file entry file entry file socket 12

17 Down (and Up) the Rabbit Hole Send Queue mbuf Socket Receive Queue mbuf Socket Layer TCP Layer IP Layer Ethernet Layer 13

18 The name of the game is to avoid copying data 14

19 The Almighty Message Buffer (mbuf) Represents a network packet! Mbuf Header! Pointer to start of data! Length of data! Mbuf Mbuf Header Packet Header Pointer to next mbuf in chain! Pointer to next mbuf in queue Data! (100 bytes) 15

20 The Almighty Message Buffer (mbuf) Represents a network packet! Packet Header Struct! Not IP Header! Only marks start of chain! Data (payload) area Mbuf Mbuf Header Packet Header Data! (100 bytes) 16

21 mbuf Chains mbufs can be chained together; chain represents one network packet! First mbuf has packet header: marks beginning of chain Mbuf Header Packet Header Mbuf Header Mbuf Header Data! (100 bytes) Data! (108 bytes) Data! (108 bytes) 17

22 Cluster mbuf (mbuf on Steroids) Field in header points to externally allocated buffer! Allows for mbuf with large data Mbuf Header Packet Header Unused Data! (2048 bytes)! (Not to Scale) 18

23 If you can chain mbufs, of what benefit is a cluster mbuf? 19

24 The Benefits of Clusters mbuf clusters can hold large amount of contiguous data! More efficient for large packets! More efficient for copying data between user and kernel space! Clusters can be shared between mbufs Mbuf Packet Unused Data! (2048 bytes) Mbuf Packet Unused 20

25 Down (and Up) the Rabbit Hole Send Queue mbuf Socket Receive Queue mbuf Socket Layer TCP Layer IP Layer Ethernet Layer 21

26 Sending Data Put data into mbuf! Mbuf Each layer prepends headers! Only adjusts data in mbuf header! Mbuf Header Packet Header Data Area 22

27 Sending Data Put data into mbuf! Mbuf Each layer prepends headers! Only adjusts data in mbuf header! Mbuf Header Packet Header Data Area Data 22

28 Sending Data Put data into mbuf! Mbuf Each layer prepends headers! Only adjusts data in mbuf header! Mbuf Header Packet Header Data Area TCP Header Data 22

29 Sending Data Put data into mbuf! Mbuf Each layer prepends headers! Only adjusts data in mbuf header! Mbuf Header Packet Header IP Data Header Area TCP Header Data 22

30 Receiving Data Remove headers from mbuf! Mbuf Only adjusts data in mbuf header! Mbuf Header Packet Header IP Data Header Area TCP Header Data 23

31 Receiving Data Remove headers from mbuf! Mbuf Only adjusts data in mbuf header! Mbuf Header Packet Header Data Area TCP Header Data 23

32 Receiving Data Remove headers from mbuf! Mbuf Only adjusts data in mbuf header! Mbuf Header Packet Header Data Area Data 23

33 Berkeley Socket API 24

34 Creating Sockets int socket (int domain, int type, int protocol); Socket is a file descriptor! Created by socket system call! Full-duplex! Domain determines protocol family (e.g, IP, AppleTalk)! Type indicates whether messages have boundaries! Protocol specifies a specific protocol within the family (TCP, UDP, ICMP, IGMP) 25

35 Setting the Endpoints Bind! (local) The (Social?) Network Connect! (remote) bind(): Sets the address of the socket s local side! connect(): Sets the address of the socket s remote side! For TCP, sends 3-way handshake 26

36 Establishing Connections Needed for connection-oriented protocols (e.g., TCP)! connect(): Starts client 3-way handshake! accept(): Accepts new connection for server! Returns new socket for that specific client! Must be done for sending/receiving data 27

37 accept() in Pictures??? Listening Socket Server 28

38 accept() in Pictures??? Listening Socket Server A Client Socket 28

39 Berkeley Sockets: I/O Sockets are file descriptors! Can use read() and write()! Can use other system calls like dup(), close()! Can use sendto() and recvfrom()! Specify to where data should go! Determine from whence data comes! Specify special options (non-blocking, out of band) 29

40 Typical TCP Client and Server Client! fd = socket ( )! connect (fd, );! Server! fd = socket ( );! bind (fd, );! fd2 = accept (fd, ); 30

41 Server Architecture 31

42 Types of Servers telnetd! sshd! ftpd! httpd! dhcpd! imapd! bootpd! popd! time! sendmail (SMTP)! echo! nfsd! daytime! bind (DNS)! quotd! ircd! chargen! ldapd! 32

43 Fork on Accept Single process waits for a connection via accept()! Create new process (thread) when a connection arrives Socket 33

44 Fork on Accept Single process waits for a connection via accept()! Create new process (thread) when a connection arrives Socket Socket 33

45 What happens if these servers are all separate programs? 34

46 Internet Super Server (inetd) Use single process to wait for connections! Hands socket off as stdin/stdout of programs! Some requests handled by inetd directly Socket Socket Socket inetd Socket 35

47 Internet Super Server (inetd) Use single process to wait for connections! Hands socket off as stdin/stdout of programs! Some requests handled by inetd directly Socket Socket Socket Socket inetd Socket telnetd 35

48 Internet Super Server (inetd) Use single process to wait for connections! Hands socket off as stdin/stdout of programs! Some requests handled by inetd directly Socket Socket Socket Socket inetd Socket Socket telnetd ftpd 35

49 What happens if you get a lot of connections (e.g., Google, the CSC 256/456 web site)? 36

50 Pre-forked/Pre-threaded Create multiple processes! All processes wait on a single socket Socket 37

51 What is the disadvantage of pre-forked/pre-threaded servers? 38

52 Security Pre-forked servers reuse processes! Stale data! Memory leaks! Processes often replaced after awhile 39

53 Network Summary Networks are like onions (and ogres!): they have layers!! Kernel must add/remove headers! Each layer solves a different problem! Network data structures designed to minimize copies! mbuf designed specifically to achieve this! Servers designed for performance and security 40