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Network Fundamentals II
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Dr. Tim Lin
ECE Department
Cal Poly Pomona
5/25/2017
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Agenda
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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
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Header
Flow Control
Error Control
Congestion Control
FTP Protocol
HTTP Protocol
SMTP Protocol
Network Commands
Technology (LAN)
IP Protocol
• The transmission mechanism at the
network layer
• Unreliable connectionless datagram
protocol
5/25/2017
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OSI
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Figure 7.1
Position of IP in TCP/IP protocol suite
Figure 7.2
IP datagram
Tools to Analyze IP Packet
• Wireshark
– http://www.wireshark.org
– Download From Dr. Rich’s CS499 site
• Ethereal
– http://www.ethereal.com
Run Wireshark
Check Frame 253 an ICMP frame (which is an IP frame)
Analyze Frame 253
First 12 bytes: Ethernet dest and rc physical addresses
Analyze 74 bytes of IP data
IP Version 4
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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
Header length = 5 * 4 = 20
Total length = 0x3c = 60
decimal. Frame = 14
ethernet + 60 IP
Protocol = 1
meaning ICMP from
chart 6
Figure 8.25
Example of checksum calculation in hexadecimal
Figure 9.1
Position of ICMP in the network layer
Figure 9.2
ICMP encapsulation
Figure 9.3
General format of ICMP messages
Ethernet type 0800
Analyze 74 bytes of ICMP data
IP Version 4
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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
ICMP Type = 8 or echo request,
agreeing with chart 9
Total length = 0x3c = 60
decimal. Frame = 14
ethernet + 60 IP
Underlined data: ICMP data
section
Header length = 5 * 4 = 20
Protocol = 1
meaning ICMP from
chart 6
Check IP Header (chart 5)
C code of ping (ICMP)
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//
// Ping.h
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#pragma pack(1)
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#define ICMP_ECHOREPLY
#define ICMP_ECHOREQ
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// IP Header -- RFC 791
typedef struct tagIPHDR
{
u_char VIHL;
u_char TOS;
short
TotLen;
short
ID;
short
FlagOff;
u_char TTL;
u_char Protocol;
u_short Checksum;
struct
in_addr iaSrc;
struct
in_addr iaDst;
}IPHDR, *PIPHDR;
0
8
// Version and IHL
// Type Of Service
// Total Length
// Identification
// Flags and Fragment Offset
// Time To Live
// Protocol
// Checksum
// Internet Address - Source
// Internet Address - Destination
Ping.h
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// ICMP Header - RFC 792
typedef struct tagICMPHDR
{
u_char
Type;
u_char
Code;
u_short
Checksum;
u_short
ID;
u_short
Seq;
char
Data;
}ICMPHDR, *PICMPHDR;
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#define REQ_DATASIZE 32
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// ICMP Echo Request
typedef struct tagECHOREQUEST
{
ICMPHDR icmpHdr;
DWORD
dwTime;
char
cData[REQ_DATASIZE];
}ECHOREQUEST, *PECHOREQUEST;
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// ICMP Echo Reply
typedef struct tagECHOREPLY
{
IPHDR
ipHdr;
ECHOREQUEST
echoRequest;
char cFiller[256];
}ECHOREPLY, *PECHOREPLY;
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#pragma pack()
// Type
// Code
// Checksum
// Identification
// Sequence
// Data
// Echo Request Data size
Ping.c (prelude)
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//
// PING.C -- Ping program using ICMP and RAW Sockets
//
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#include <stdio.h>
#include <stdlib.h>
#include <winsock.h>
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#include "ping.h"
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// Internal Functions
void Ping(LPCSTR pstrHost);
void ReportError(LPCSTR pstrFrom);
int WaitForEchoReply(SOCKET s);
u_short in_cksum(u_short *addr, int len);
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// ICMP Echo Request/Reply functions
int
SendEchoRequest(SOCKET, LPSOCKADDR_IN);
DWORD
RecvEchoReply(SOCKET, LPSOCKADDR_IN, u_char *);
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Ping.c main function
// main()
void main(int argc, char **argv)
{
WSADATA wsaData;
WORD wVersionRequested = MAKEWORD(1,1);
int nRet;
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// Check arguments
if (argc != 2)
{
fprintf(stderr,"\nUsage: ping hostname\n");
return;
}
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// Init WinSock
nRet = WSAStartup(wVersionRequested, &wsaData);
if (nRet)
{
fprintf(stderr,"\nError initializing WinSock\n");
return;
}
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// Check version
if (wsaData.wVersion != wVersionRequested)
{
fprintf(stderr,"\nWinSock version not supported\n");
return;
}
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// Go do the ping
Ping(argv[1]);
Ping function first part
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void Ping(LPCSTR pstrHost)
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{
SOCKET
rawSocket;
LPHOSTENT lpHost;
struct sockaddr_in saDest;
struct sockaddr_in saSrc;
DWORD
dwTimeSent;
DWORD
dwElapsed;
u_char cTTL;
int
nLoop;
int
nRet;
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// Create a Raw socket
rawSocket = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP);
if (rawSocket == SOCKET_ERROR)
{
ReportError("socket()");
return;
}
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// Tell the user what we're doing
printf("\nPinging %s [%s] with %d bytes of data:\n",
pstrHost,
inet_ntoa(saDest.sin_addr),
// 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;
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Ping function part II
// Ping multiple times
for (nLoop = 0; nLoop < 4; nLoop++)
{
// Send ICMP echo request
SendEchoRequest(rawSocket, &saDest);
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// Use select() to wait for data to be received
nRet = WaitForEchoReply(rawSocket);
if (nRet == SOCKET_ERROR)
{
ReportError("select()");
break;
}
if (!nRet)
{
printf("\nTimeOut");
break;
}
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// Receive reply
dwTimeSent = RecvEchoReply(rawSocket, &saSrc, &cTTL);
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// 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()");
}
Send Echo Request
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// 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;
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// Fill in echo request
echoReq.icmpHdr.Type
echoReq.icmpHdr.Code
echoReq.icmpHdr.Checksum = 0;
echoReq.icmpHdr.ID
echoReq.icmpHdr.Seq
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// Fill in some data to send
for (nRet = 0; nRet < REQ_DATASIZE; nRet++)
echoReq.cData[nRet] = ' '+nRet;
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// Save tick count when sent
echoReq.dwTime
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// Put data in packet and compute checksum
echoReq.icmpHdr.Checksum = in_cksum((u_short *)&echoReq, sizeof(ECHOREQUEST));
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// Send the echo request
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nRet = sendto(s,
= ICMP_ECHOREQ;
= 0;
= nId++;
= nSeq++;
= GetTickCount();
(LPSTR)&echoReq,
sizeof(ECHOREQUEST),
0,
/* flags */
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(LPSOCKADDR)lpstToAddr, /* destination */
sizeof(SOCKADDR_IN)); /* address length */
if (nRet == SOCKET_ERROR)
ReportError("sendto()");
return (nRet);
/* socket */
/* buffer */
Receive Echo Reply
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// 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);
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// Receive the echo reply
nRet = recvfrom(s,
(LPSTR)&echoReply,
sizeof(ECHOREPLY),
0,
// socket
// buffer
// size of buffer
// flags
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(LPSOCKADDR)lpsaFrom,// From address
&nAddrLen);
//
pointer to address len
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// Check return value
if (nRet == SOCKET_ERROR)
ReportError("recvfrom()");
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// return time sent and IP TTL
*pTTL = echoReply.ipHdr.TTL;
return(echoReply.echoRequest.dwTime);
}
Ping.c: Report Error
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// What happened?
void ReportError(LPCSTR pWhere)
{
fprintf(stderr,"\n%s error: %d\n",
WSAGetLastError());
}
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// WaitForEchoReply()
// Use select() to determine when
// data is waiting to be read
int WaitForEchoReply(SOCKET s)
{
struct timeval Timeout;
fd_set readfds;
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readfds.fd_count = 1;
readfds.fd_array[0] = s;
Timeout.tv_sec = 5;
Timeout.tv_usec = 0;
return(select(1, &readfds, NULL, NULL, &Timeout));
}
Ping.c Checksum
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// Mike Muuss' in_cksum() function
// and his comments from the original
// ping program
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// * Author // *
Mike Muuss
// *
U. S. Army Ballistic Research Laboratory
// *
December, 1983
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/*
*
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* Checksum routine for Internet Protocol family headers (C Version)
*
*/
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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;
IN_CKSUM
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/*
* 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;
}
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/* mop up an odd byte, if necessary */
if( nleft == 1 ) {
u_short
u = 0;
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}
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/*
* 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);
answer = ~sum;
return (answer);
*(u_char *)(&u) = *(u_char *)w ;
sum += u;
/* add carry */
/* truncate to 16 bits */
Figure 8.1
Position of ARP in TCP/IP protocol suite
Figure 8.2
ARP operation
Figure 8.3
ARP packet
Figure 8.5
Four cases using ARP
Figure 8.6
Example 8.1
Note Ethernet Type bytes are
0806 for ARP, different from IP
packet of 0800
ARP Reply Frame
Did you see 0806 in ethernet type?