1. Internet: network nodes
Host: any computer executing protocol
Hub: repeats signal heard one each port to all ports.
Bridge: understands physical layer addresses, MAC addresses, and learns where
each device is located. It listens to all traffic on LAN. If it finds that packet should
go to another segment it forwards the frame to it. It is store-and-forward device.
Switch: same as bridge however much faster. It redirects a frame only after reading
destination address on a ongoing basis.
Router: Internetwork layer device. It reads entire packet, based on destination
address finds the best route for the packet and sends it.

2. Internet: network of networks
star
star
hub
bridge
hub
token
ring
switch
bridge
bridge
Ethernet
Ethernet
router

3. Internet protocol stack vs. OSI model (Fig. 1.2)
Physical Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Application Layer
Process Layer
, FTP, HTTP
Host-to-host Layer
TCP, UDP
Internet Layer
IP, ARP
MAC* Layer
Ethernet, Token ring (ATM, Frame Relay**)
Physical Layer
Manchester
* Medium Access Control. MAC and Physical layers are called Network Interface Layer.
** not exactly MAC, however, layer above physical

4. Two networks connected with a router (Fig. 1.3)
Ethernet host
Token ring host
FTP
client
FTP protocol
FTP
server
TCP
TCP protocol
TCP
router IP
IP protocol IP
IP protocol IP
Ethernet
driver
Ethernet
protocol
Ethernet
driver
Token ring
driver
Ethernet
protocol
Token ring
driver
Ethernet
Token ring

5. Internet protocol suite
Telnet
BOOTP
HTTP
DHCP
TFTP
SNMP
FTP
DNS
RIP
Process Layer
Port Numbers
/ / /
Host to Host
Layer
TCP
UDP 6 17
ICMP 01
OSPF
IGRP 88
Protocol
Codes 89
Internet Layer
ARP IP
RARP
0806
0800
0806
Network
Interface
Layer
Ethernet, Token Ring, FDDI, SLIP, PPP, etc.

6. Internet protocols
TELNET - remote terminal connection service. Allows user terminal to mimic the terminal
at the remote side.
FTP - File Transfer Protocol (put/get file to/from remote machine).
HTTP - Hypertext Transport Protocol.
DNS - Domain Name Server On-line distributed database for translating IP machine names
into IP addresses.
BOOTP - Bootstrap Protocol defines each device autoconfiguration on the server (improvement
to the RARP).
DHCP - Dynamic Host Configuration Protocol (improvement to BOOTP) allows network
administrator to configure workstation by providing dynamic address assignment.
TFTP - Trivial File Transfer Protocol (same as FTP with minimal capability).
SNMP - Simple Network Monitoring Protocol used to monitor IP gateways and networks they
are attached to.
RIP - Routing Information Protocol used to exchange the routing information among small
set of computers (every 30 sec hosts exchange information).
TCP - reliable Transmission Control Protocol (connection oriented).
UDP - unreliable Universal Transport Protocol (connectionless).
IGRP - Interior Gateway Routing Protocol (proprietary routing protocol developed by Cisco).
ICMP - Internet Control Message Protocol part of IP that handles error and control messages.
OSPF - Open Shortest Path First routing protocol.
ARP - Address Resolution Protocol used to dynamically bind IP addresses to physical addresses.
RARP - Reverse ARP used by newly installed machine to find its IP address.
IP - Internet Protocol.

7. Encapsulation (Fig. 1.7) UDP 8 bytes variable Application Ethernet
20 to 60 bytes
IP header
TCP
20 or 24
variable
Application
CRC
4 bytes
ICMP
6 + bytes

8. Demultiplexing (Fig. 1.8) application TCP IP Ethernet driver UDP ICMP
incoming frame
IGMP
RARP
ARP

9. Sample (book) network Solaris 2.2 SunOS 4.1.1 aix .1.92 Cisco router
gemini
gateway
.1.32
.1.11
.1.4
Ethernet
netb
.1.183
Telebit
NetBlazer
modem
All IP addresses belong to class B network ID xxx.xxx
SLIP (dialup)
modem
BSD/
BSD/
SunOS 4.1.3
.1.29
SVR4
slip
bsdi
sun
svr4
.13.65
.13.66
.13.35
.13.33
.13.34
Ethernet

10. Link Layer (Fig. 2.1) SLIP (Serial Line IP) c0 db ESC c0 db dc db dd
Point-to-point (PPP) protocol
Flag 7E
addr FF
Contr 03
Flag 7E
protocol
data
CRC
up to
0021
IP datagram
C021
Link control data
8021
network control data

11. Ethernet Header Destin. Addr. Source Addr. Type
ff ff ff ff ff ff c0 a
Broadcast
Unicast
ARP
e c0 a
Multicast
Unicast IP
c0 a c a c
Unicast
Unicast
SNMP
Vendor addr
component
Vendor ser.
number

12. IP addressing convention
4 bytes (dec): =
Class A: Large networks (GM, Ford, etc)
N-Network bits
L-Locally administered
126 Class A networks
16,777,214 hosts/network
0NNNNNNN LLLLLLLL LLLLLLLL LLLLLLLL
0 - unused, ; loop back
Class B: medium size (universities, medium business)
16,384 Class B networks
65,534 hosts/network
(0 not used, all 1’s broadcast)
10NNNNNN NNNNNNNN LLLLLLLL LLLLLLLL
Class C: small networks (small business)
2,097,152 Class C networks
254 hosts/network
110NNNNN NNNNNNNN NNNNNNNN LLLLLLLL
Class D: broadcasting
2,097,152 Class C networks
254 hosts/network
1110MMMM MMMMMMMM MMMMMMMM MMMMMMMM

13. IP subnetting with subnet masks
IP address:
Subnet mask:
Binary addr:
Binary Mask:
Address bits: NNNNNNNN NNNNNNNN SSSSSSI I I I I I I I I I
N - network bits
S - subnet bits
I - Interface bits.
Natural masks:
Class A :
B :
C :

14. Subnetting example Are this two hosts in the same subnet?
source:
target:
mask:
248 = mask
121 = source
subn= source subnet
248 = target
subn= target subnet