Understand IPv4 Addressing

1. Understand IPv4 Addressing

2. IPv4: originally Classfull Addressing • Special address • Host ID = 0: network address • Network ID = 0, host ID = 0 • i.e 0.0.0.0 means this network • 127.x.y.z : “looped back” • Host ID = all 1s : broadcasting • NAT address • 10/8 • 172.16/12 • 192.168/12 • Broadcast address • 255.255.255.255 • Limited broadcast • router 밖에는 나가지 못함 • 190.50.255.255 • Network-directed broadcast • 그 네트워크까지 가서 네트워크 내에 broadcast • 190.50.1.255/24 • Subnet-directed broadcast • 190.50.1.0/24 subnet 내에 broadcast IPv4 address는 host의 address 가 아니라 interface의 address이다.

3. 223.1.0.0/16 Subnet 223.1.1.0/24 223.1.2.0/24 • Network address IP address && mask • Network ID 223.1.1.1 223.1.2.1 223.1.1.2 223.1.2.9 223.1.1.4 223.1.2.2 223.1.1.3 223.1.3.27 subnet 223.1.3.2 223.1.3.1 223.1.3.0/24 network consisting of 3 subnets • CIDR (Classless Inter-Domain Routing) • Subnetting + suppernetting

4. Tip: Develop and Use Application “Skeletons”

5. Simple TCP Client and Server Server: simples.c Client: simplec.c

6. Making UNIX/Windows Compatible UNIX: bsd/skel.h Windows: win/skel.h wincompat.c: Window에서 socket을생성전에 call해야

7. “mclab.hufs.ac.kr” or “203.254.68.114” or “” -- server “http” or “80” TCP Server Skeleton tcpserver.skel:

8. TCP Server Skeleton - Cont’d Usage: % myserver [local_addr | local_name] {local_port | service} Example: %myserver 15000 %myserver localhost http

9. TCP Client Skeleton tcpclient.skel: Usage: % myclient {peer_addr | peer_name} {peer_port | service} Example: % myclient 203.253.70.5 15000 % myclient www.hufs.ac.kr http

10. UDP Server & Client Skeleton udpserver.skel: udpclient.skel:

11. Build Your Own Library and Use It ! etcp.h

12. TCP Client & Server Starting Functions Host name or IP addr or “” (my addr for server) “http” or “80”

13. UDP Client & Server Starting Functions

14. Remember thatTCP is a Stream Protocol

15. TCP is a Stream Protocol • No message boundary, just a byte stream • TCP application에서 하나의 message를 send()했다고 해서 recevier application에서 그 message를 한 덩어리로 recv()되는 것이 아니다. • Message를 send()했어도 TCP segment에 언제, 어떻게 실릴지 모른다. (buffering 되기 때문) • Recv()하면 몇 byte 읽힐지 모른다. • If you want to read exactly n bytes ?? • If you want to make a record ??? • Use end-of-record mark. e.g) new line • Handle variable records (using fixed header) 메시지를 읽을 user buffer의 크기 즉, 최대로 읽을 수 있는 크기 #include <sys/socket.h> /* UNIX */ #include <winsock2.h> /* Windows */ int recv (SOCKET s, void *buf, size_t bufsize, int flags); int read (SOCKET s, void *buf, size_t bufsize); /* UNIX */ Returns: # of bytes read (>0), 0 if received FIN and no more data, -1 on failure int send (SOCKET s, const void *buf, size_t len, int flags); int write (SOCKET s, const void *buf, size_t len); /* UNIX */ Returns: # of bytes transferred on success, -1 on failure Socket send buffer에 저장할 메시지 길이

16. Use End-of-record mark: read a line lib/readline.c:

17. Read n bytes and Read a variable-length record lib/readvrec: Network byte order lib/readn.c: Header size len cnt bp #include “etcp.h” int readn (SOCKET s, char *buf, size_t len); Returns: # of bytes read, -1 on failure int readvrec (SOCKET s, char *buf, size_t len); Returns: # of bytes read , -1 on failure Record Length Other Header Data Variable Data

18. Example: Client/Server using variable records vrs.c: vrc.c: