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CS4231 Local Area Networks HW2 – PC-Based Bridge

CS4231 Local Area Networks HW2 – PC-Based Bridge. Overview. LAN 1. LAN 2. Summary. 目的 連接 LAN1 與 LAN2 Frame forwarding Frame filtering Hint Data link layer socket programming Library: libpcap libnet. Bridge. Layer 2 network device Connect 2 LAN. Network API - libpcap.

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CS4231 Local Area Networks HW2 – PC-Based Bridge

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  1. CS4231Local Area NetworksHW2 – PC-Based Bridge

  2. Overview LAN 1 LAN 2

  3. Summary • 目的 • 連接LAN1與LAN2 • Frameforwarding • Framefiltering • Hint • Data link layer socket programming • Library: • libpcap • libnet

  4. Bridge • Layer 2 network device • Connect 2 LAN

  5. Network API - libpcap • libpcap (Packet CAPture) provides a portable framework for low-level network monitoring. • Applications include network statistics collection, security monitoring, network debugging, etc. • libpcap is the library we are going to use to grab packets right as they come off of the network card • Tutorial • http://yuba.stanford.edu/~casado/pcap/section1.html

  6. Libpcap - Functions • pcap_t * pcap_open_live(char *device, int snaplen, int promisc, int to_ms, char *ebuf) • int pcap_dispatch(pcap_t *p, int cnt, pcap_handler callback, u_char *user)

  7. libpcap -Open up NIC for PCAP dev = pcap_lookupdev(errbuf); // 亦可寫成 dev = “eth0” If(dev == NULL) { fprintf(stderr,“%s\n”,errbuf); return -1; } descr = pcap_open_live(dev, BUFSIZ, promisc, pcap_time_out, errbuf); If(descr == NULL) { printf(“pcap_open_live(): %s\n”,errbuf); return -1; }

  8. libpcap - Capture a Packet int ret; ret = pcap_dispatch( pt_a, 0, dev_a_handle, NULL); if ( ret == -1 ) { pcap_perror( pt_a, "pcap_dispatch err:"); } void dev_a_handle( u_char *devId, const struct pcap_pkthdr *hdr, const u_char *packet )

  9. Network API - libnet • Designed by Mike Schiffman, libnet is a portable, open source, C-language library for creating and injecting network packets. • libnet supports packet creation at all network levels with the TCP/IP network model.

  10. libnet - Functions • libnet_t *libnet_init(int injection_type, char *device, char *err_buf); • int libnet_write_link(struct libnet_link_int *l,const u_char *device, u_char *packet,int packet_size);

  11. libnet - Initialization net_b = libnet_init( LIBNET_LINK, "eth0", errbuf ); if( net_a == NULL ) { fprintf(stderr, "libnet_init fail:%s ", errbuf ); return; }

  12. libnet - Send a Packet c = libnet_write_link( net_b, (u_char*)packet, hdr->caplen );

  13. pthread • int pthread_create(pthread_t * thread, const pthread_attr_t * attr, void * (*start_routine)(void *), void *arg); • thread - returns the thread id. (unsigned long int defined in bits/pthreadtypes.h) • attr - Set to NULL if default thread attributes are used. • void * (*start_routine) - pointer to the function to be threaded. Function has a single argument: pointer to void. • *arg - pointer to argument of function. To pass multiple arguments, send a pointer to a structure.

  14. pthread • int pthread_join(pthread_t * thread, void **value_ptr); • The pthread_join() function suspends execution of the calling thread until the target thread terminates

  15. libpcap, libnet Installation • Clean & update the package list • sudo apt-get clean • sudo apt-get update • flex, bison • sudo apt-get flex • sudo apt-get bison • libpcap • sudo apt-get install libpcap0.8-dev • libnet • sudo apt-get install libnet1-dev • Remember to Install these two library first

  16. Programming Environment • You have to write your program on Linux platform. • You can install VMware to run Linux on it.

  17. Environment Construction • 一台有兩張網卡的電腦 (PC_E) • 其他電腦用連接至 PC_E • PC_E 需安裝 Linux作業系統以及 • libpcap, libnet • 亦可在 Windows 下使用 VMware 安裝 Linux 代替PC_E • 仍須兩張網路卡 • 使 Virtual Machine 的兩張虛擬網路卡分別橋接至兩張實體網路卡

  18. Edit VM Setting

  19. Add a Host Virtual Adapters

  20. Add a Ethernet Card 建立兩個 subnet

  21. Add a Ethernet Card

  22. Add a Ethernet Card

  23. Add a Ethernet Card 兩張網卡分別對應到eth0, eth1

  24. Bridge Guest NIC to Host NIC 兩張網卡分別bridged 到 VMnet2, VMnet3

  25. Requirements • 秀出 bridge 的 filtering database • (工作站位址, 隸屬埠, 登錄時間) • 同一個 LAN 互傳(該兩台電腦都已經被 bridge 學習了)時，另一 LAN 不應該收到封包 • 兩邊的 LAN 可以互通

  26. Debugging

  27. Grading • Correctness (60%) • Report (30%) • How to run your program. • What you’ve learned? • What are you suffer from this HW? • Any feedback? • Coding Style (10%)

  28. Hand in your program • Deadline: 自行練習

  29. Appendix • libpcap / libnet • http://web.zyline.com.cn/prolist.asp?id=4916 • http://dev.csdn.net/article/21/21009.shtm • pthread • http://www.yolinux.com/TUTORIALS/LinuxTutorialPosixThreads.html

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