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Network Fundamentals II

Network Fundamentals II. Dr. Tim Lin ECE Department Cal Poly Pomona. Add Corporate Logo Here. 1/3/2020. >. EXIT. Agenda. What is Computer Network ISO / OSI model Internet Organizations IP Addresses v4 Classful Classless V6 IP Protocol Header ICMP Protocol ARP Protocol.

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Network Fundamentals II

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  1. Network Fundamentals II Dr. Tim Lin ECE Department Cal Poly Pomona Add CorporateLogoHere 1/3/2020 > EXIT

  2. Agenda What is Computer Network ISO / OSI model Internet Organizations IP Addresses v4 Classful Classless V6 IP Protocol Header ICMP Protocol ARP Protocol • UDP Protocol • TCP Protocol • Header • Flow Control • Error Control • Congestion Control • FTP Protocol • HTTP Protocol • SMTP Protocol • Network Commands • Technology (LAN)

  3. IP Protocol The transmission mechanism at the network layer Unreliable connectionless datagram protocol 1/3/2020 < > OSI EXIT

  4. Figure 7.1Position of IP in TCP/IP protocol suite

  5. Figure 7.2IP datagram

  6. Tools to Analyze IP Packet Wireshark http://www.wireshark.org Download From Dr. Rich’s CS499 site Ethereal http://www.ethereal.com

  7. Run Wireshark

  8. Check Frame 253 an ICMP frame (which is an IP frame)

  9. Analyze Frame 253

  10. First 12 bytes: Ethernet dest and rc physical addresses

  11. Analyze 74 bytes of IP data 0000 00 06 25 8f ac 55 00 0f 1f 4f 21 7a 08 00 45 00 ..%..U.. .O!z..E. 0010 00 3c b5 f2 00 00 80 01 ca f6 c0 a8 01 6e 62 89 .<...... .....nb. 0020 95 38 08 00 30 5c 02 00 1b 00 61 62 63 64 65 66 .8..0\.. ..abcdef 0030 67 68 69 6a 6b 6c 6d 6e 6f 70 71 72 73 74 75 76 ghijklmn opqrstuv 0040 77 61 62 63 64 65 66 67 68 69 wabcdefg hi IP Version 4 Header length = 5 * 4 = 20 Total length = 0x3c = 60 decimal. Frame = 14 ethernet + 60 IP Protocol = 1 meaning ICMP from chart 6

  12. Figure 8.25Example of checksum calculation in hexadecimal

  13. Figure 9.1Position of ICMP in the network layer

  14. Figure 9.2ICMP encapsulation

  15. Figure 9.3General format of ICMP messages

  16. Analyze 74 bytes of ICMP data 0000 00 06 25 8f ac 55 00 0f 1f 4f 21 7a 08 00 45 00 ..%..U.. .O!z..E. 0010 00 3c b5 f2 00 00 80 01 ca f6 c0 a8 01 6e 62 89 .<...... .....nb. 0020 95 38 08 00 30 5c 02 00 1b 0061 62 63 64 65 66 .8..0\.. ..abcdef 0030 67 68 69 6a 6b 6c 6d 6e 6f 70 71 72 73 74 75 76 ghijklmn opqrstuv 0040 77 61 62 63 64 65 66 67 68 69 wabcdefg hi Ethernet type 0800 IP Version 4 Underlined data: ICMP data section ICMP Type = 8 or echo request, agreeing with chart 9 Header length = 5 * 4 = 20 Total length = 0x3c = 60 decimal. Frame = 14 ethernet + 60 IP Protocol = 1 meaning ICMP from chart 6

  17. C code of ping (ICMP) // // Ping.h // #pragma pack(1) #define ICMP_ECHOREPLY 0 #define ICMP_ECHOREQ 8 // IP Header -- RFC 791 typedef struct tagIPHDR { u_char VIHL; // Version and IHL u_char TOS; // Type Of Service short TotLen; // Total Length short ID; // Identification short FlagOff; // Flags and Fragment Offset u_char TTL; // Time To Live u_char Protocol; // Protocol u_short Checksum; // Checksum struct in_addr iaSrc; // Internet Address - Source struct in_addr iaDst; // Internet Address - Destination }IPHDR, *PIPHDR; Check IP Header (chart 5)

  18. Ping.h // ICMP Header - RFC 792 typedef struct tagICMPHDR { u_char Type; // Type u_char Code; // Code u_short Checksum; // Checksum u_short ID; // Identification u_short Seq; // Sequence char Data; // Data }ICMPHDR, *PICMPHDR; #define REQ_DATASIZE 32 // Echo Request Data size // ICMP Echo Request typedef struct tagECHOREQUEST { ICMPHDR icmpHdr; DWORD dwTime; char cData[REQ_DATASIZE]; }ECHOREQUEST, *PECHOREQUEST; // ICMP Echo Reply typedef struct tagECHOREPLY { IPHDR ipHdr; ECHOREQUEST echoRequest; char cFiller[256]; }ECHOREPLY, *PECHOREPLY; #pragma pack()

  19. Ping.c (prelude) // // PING.C -- Ping program using ICMP and RAW Sockets // #include <stdio.h> #include <stdlib.h> #include <winsock.h> #include "ping.h" // Internal Functions void Ping(LPCSTR pstrHost); void ReportError(LPCSTR pstrFrom); int WaitForEchoReply(SOCKET s); u_short in_cksum(u_short *addr, int len); // ICMP Echo Request/Reply functions int SendEchoRequest(SOCKET, LPSOCKADDR_IN); DWORD RecvEchoReply(SOCKET, LPSOCKADDR_IN, u_char *);

  20. Ping.c main function // main() void main(int argc, char **argv) { WSADATA wsaData; WORD wVersionRequested = MAKEWORD(1,1); int nRet; // Check arguments if (argc != 2) { fprintf(stderr,"\nUsage: ping hostname\n"); return; } // Init WinSock nRet = WSAStartup(wVersionRequested, &wsaData); if (nRet) { fprintf(stderr,"\nError initializing WinSock\n"); return; } // Check version if (wsaData.wVersion != wVersionRequested) { fprintf(stderr,"\nWinSock version not supported\n"); return; } // Go do the ping Ping(argv[1]); // Free WinSock WSACleanup(); }

  21. Ping function first part void Ping(LPCSTR pstrHost) { SOCKET rawSocket; LPHOSTENT lpHost; struct sockaddr_in saDest; struct sockaddr_in saSrc; DWORD dwTimeSent; DWORD dwElapsed; u_char cTTL; int nLoop; int nRet; // Create a Raw socket rawSocket = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP); if (rawSocket == SOCKET_ERROR) { ReportError("socket()"); return; } // Lookup host lpHost = gethostbyname(pstrHost); if (lpHost == NULL) { fprintf(stderr,"\nHost not found: %s\n", pstrHost); return; } // Setup destination socket address saDest.sin_addr.s_addr = *((u_long FAR *) (lpHost->h_addr)); saDest.sin_family = AF_INET; saDest.sin_port = 0; // Tell the user what we're doing printf("\nPinging %s [%s] with %d bytes of data:\n", pstrHost, inet_ntoa(saDest.sin_addr), REQ_DATASIZE);

  22. Ping function part II // Ping multiple times for (nLoop = 0; nLoop < 4; nLoop++) { // Send ICMP echo request SendEchoRequest(rawSocket, &saDest); // Use select() to wait for data to be received nRet = WaitForEchoReply(rawSocket); if (nRet == SOCKET_ERROR) { ReportError("select()"); break; } if (!nRet) { printf("\nTimeOut"); break; } // Receive reply dwTimeSent = RecvEchoReply(rawSocket, &saSrc, &cTTL); // Calculate elapsed time dwElapsed = GetTickCount() - dwTimeSent; printf("\nReply from: %s: bytes=%d time=%ldms TTL=%d", inet_ntoa(saSrc.sin_addr), REQ_DATASIZE, dwElapsed, cTTL); } printf("\n"); nRet = closesocket(rawSocket); if (nRet == SOCKET_ERROR) ReportError("closesocket()"); }

  23. Send Echo Request // SendEchoRequest() // Fill in echo request header // and send to destination int SendEchoRequest(SOCKET s,LPSOCKADDR_IN lpstToAddr) { static ECHOREQUEST echoReq; static nId = 1; static nSeq = 1; int nRet; // Fill in echo request echoReq.icmpHdr.Type = ICMP_ECHOREQ; echoReq.icmpHdr.Code = 0; echoReq.icmpHdr.Checksum = 0; echoReq.icmpHdr.ID = nId++; echoReq.icmpHdr.Seq = nSeq++; // Fill in some data to send for (nRet = 0; nRet < REQ_DATASIZE; nRet++) echoReq.cData[nRet] = ' '+nRet; // Save tick count when sent echoReq.dwTime = GetTickCount(); // Put data in packet and compute checksum echoReq.icmpHdr.Checksum = in_cksum((u_short *)&echoReq, sizeof(ECHOREQUEST)); // Send the echo request nRet = sendto(s, /* socket */ (LPSTR)&echoReq, /* buffer */ sizeof(ECHOREQUEST), 0, /* flags */ (LPSOCKADDR)lpstToAddr, /* destination */ sizeof(SOCKADDR_IN)); /* address length */ if (nRet == SOCKET_ERROR) ReportError("sendto()"); return (nRet); }

  24. Receive Echo Reply // Receive incoming data // and parse out fields DWORD RecvEchoReply(SOCKET s, LPSOCKADDR_IN lpsaFrom, u_char *pTTL) { ECHOREPLY echoReply; int nRet; int nAddrLen = sizeof(struct sockaddr_in); // Receive the echo reply nRet = recvfrom(s, // socket (LPSTR)&echoReply, // buffer sizeof(ECHOREPLY), // size of buffer 0, // flags (LPSOCKADDR)lpsaFrom, // From address &nAddrLen); // pointer to address len // Check return value if (nRet == SOCKET_ERROR) ReportError("recvfrom()"); // return time sent and IP TTL *pTTL = echoReply.ipHdr.TTL; return(echoReply.echoRequest.dwTime); }

  25. Ping.c: Report Error // What happened? void ReportError(LPCSTR pWhere) { fprintf(stderr,"\n%s error: %d\n", WSAGetLastError()); } // WaitForEchoReply() // Use select() to determine when // data is waiting to be read int WaitForEchoReply(SOCKET s) { struct timeval Timeout; fd_set readfds; readfds.fd_count = 1; readfds.fd_array[0] = s; Timeout.tv_sec = 5; Timeout.tv_usec = 0; return(select(1, &readfds, NULL, NULL, &Timeout)); }

  26. Ping.c Checksum // // Mike Muuss' in_cksum() function // and his comments from the original // ping program // // * Author - // * Mike Muuss // * U. S. Army Ballistic Research Laboratory // * December, 1983 /* * I N _ C K S U M * * Checksum routine for Internet Protocol family headers (C Version) * */ u_short in_cksum(u_short *addr, int len) { register int nleft = len; register u_short *w = addr; register u_short answer; register int sum = 0; /* * Our algorithm is simple, using a 32 bit accumulator (sum), * we add sequential 16 bit words to it, and at the end, fold * back all the carry bits from the top 16 bits into the lower * 16 bits. */ while( nleft > 1 ) { sum += *w++; nleft -= 2; } /* mop up an odd byte, if necessary */ if( nleft == 1 ) { u_short u = 0; *(u_char *)(&u) = *(u_char *)w ; sum += u; } /* * add back carry outs from top 16 bits to low 16 bits */ sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */ sum += (sum >> 16); /* add carry */ answer = ~sum; /* truncate to 16 bits */ return (answer); }

  27. Figure 8.1Position of ARP in TCP/IP protocol suite

  28. Figure 8.2ARP operation

  29. Figure 8.3ARP packet

  30. Figure 8.5Four cases using ARP

  31. Figure 8.6Example 8.1 Note Ethernet Type bytes are 0806 for ARP, different from IP packet of 0800

  32. ARP Reply Frame Did you see 0806 in ethernet type?

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