source router Destination IP packet IP packet fragments Reassembly Required Fragments Created.

Protocol Levels

TCP Header Data

DataEthernet Header

IP Header Data

HTTP: Packet

TCP/IP Protocols

MAC Layer (Ethernet)

TCP UDP ICMP

IP ARP

SMTP Telnet

FTP HTTP

DHCPDNS

PINGSNMPPOP

source

router

router

Destination

IP packet

IP packet fragments

Reassembly Required

Fragments Created

TCP

• Connection Oriented– state

• Stream Oriented– Sequence number

• Full Duplex

• Reliable– acknowledgment

TCP Commands

• Syn – synchronize sequence numbers

• Ack – acknowledgement

• Fin – close connection

• Push – send data immediately

• Urgent – look at data out of sequence

• Reset – reject connection

TCP Connection

• Passive Open– Server opens known port and waits for client to

connect (no traffic on network)

• Active open– Client opens any available port and connects to

server on known port (starts three way handshake)

TCP Connection States

LISTEN Server waiting

SYN-SENT Waiting for ack

SYN-RCVD Syn received

ESTABLISHED Connection established

FIN-WAIT-1 Closing requested

FIN-WAIT-2 Closing accepted

CLOSE-WAIT Server waiting for client to close

LAST-ACK Server waiting for last ack

CLOSED

LISTEN

ESTABLISHED

SYN-SENT

CLOSE-WAIT

SYN-RCVD

FIN-WAIT-1

LAST-ACK

FIN-WAIT-2

TIME-WAIT

Passive openActive open/syn

Syn/ syn+ack

Syn+ack/ack

Close/fin

Ack/

timeout

Fin/ack

ack

ack

Close/fin

Fin/ack

TCP Sliding Window

• Sequence No. - number of first byte in the segment

• Acknowledgement – number of next byte expected

• Sliding Window – number of bytes that can be transmitted without an acknowledgement

K S U G O L D E N F L A S H E S

Sliding Window

Sliding Window

Sender

Receiver

K S U G O L D E N F L A S H E S

K S U

Sliding Window Ready to send

Sent, not yet acked

K S U G O L D E N F L A S H E S

K S U D E N F L A

Sent and

ACKed

Sliding Window Ready to send

Sent, not yet acked

K S U G O L D E N F L A S H E S

K S U G O L D E N F L A

Sent and

ACKed

Sliding Window

Syn

ClientServer

Seq 7280

Client sends syn to open connection

Syn

ClientServer

Syn, Ack

Server sends Ack and Syn

Seq 5965 Ack 7281

Syn

ClientServer

Syn, Ack

Ack Cient sends Ack, connection is established

Seq 7281 Ack 5966

Syn

ClientServer

Syn, Ack

AckAck, Push Client requests Web Page

Seq 7281 Ack 5966

Syn

ClientServer

Syn, Ack

AckAck

AckServer sends first part of Web

Page

Seq 5966 ack 7532

Syn

ClientServer

Syn, Ack

AckAck

Ack

Ack

Ack

Server sends remainder of page

Seq 5966 ack 7531

Seq 7426 ack 7531

Syn

ClientServer

Syn, Ack

AckAck

Ack

Ack

Ack

Ack Client sends ack

Seq 7531 ack 8886

Syn

ClientServer

Syn, Ack

AckAck

Ack

Ack

Ack

Ack

Ack, Fin, Push

Server starts closing of connection

Seq 8886 ack 7531

Syn

ClientServer

Syn, Ack

AckAck

Ack

Ack

Ack

Ack

Ack, Fin, Push

Ack Client acks closing of server’s side of connection

Seq 7531 ack 9203

Syn

ClientServer

Syn, Ack

AckAck

Ack

Ack

Ack

Ack

Ack, Fin, Push

Ack

Ack, Fin Client requests closing of its side of connection

Seq 7531 ack 9203

Syn

ClientServer

Syn, Ack

AckAck

Ack

Ack

Ack

Ack

Ack, Fin, Push

Ack

Ack, Fin

Ack

Server sends Ack, connection closed

Seq 9203 ack 7532

ARP

ARP Request(broadcast)

Who is 131.123.8.8 ?

ARP

ARP Response(unicast)

I am 131.123.8.8, HA= 00-C0-4F-AB-DA-0C

http://www.rhyshaden.com/arp.htm

DHCP

DHCP Request(broadcast)

DHCP Server

DHCP Client

DHCP

DHCP Response(Unicast)

DHCP Server

DHCP Client

IP 131.123.8.173Mask: 255.255.255.0Router: 131.123.8.10DNS: 131.123.1.1 131.123.4.23

TYPE

IDENTIFIER

OPTIONAL DATA

SEQUENCE NUMBER

CODE CHECKSUM

0 8 16 31

ICMP Echo message

ftp client ftp server

Proto Local Address Foreign Address TCP 131.123.8.111:2349 131.123.250.211:21

TCP 131.123.8.111:2353 131.123.250.211:20

2349 212353 20

TCP Segments

131.123.8.111

131.123.250.211