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Network Basics
CS490 - Security in Computing
Copyright © 2005 by Scott Orr and the
Trustees of Indiana University
Section Overview
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Network terms and topologies
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OSI and TCP/IP Protocol Stacks
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Ethernet and TCP/IP Packets
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Addressing and Name Resolution
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Routing
References
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Security in Computing, 3rd Ed.
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Chapter 7 (pgs. 363-403)
Basic Networking Terms
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Hosts & Nodes
Links & Media
Protocols
LANs, MANs, & WANs
Internets and Intranets
Network Topologies
Bus
Star
Ring
OSI Network Model
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Data Link
Data Link
Physical
Physical
TCP/IP Protocol Stack
Application (FTP, HTTP, DNS)
Transport Layer (TCP,UDP)
Network Layer (IP)
Link Layer (Device Drivers)
Physical Layer (media)
TCP/IP Packet Encapsulation
Service
Data
TCP/UDP
IP
Ethernet/PPP
UTP/PSTN
E
T/U
Data
IP T/U
Data
IP T/U
Data
E
IP Addresses
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Unique for each connection (interface)
Consists of 4 octets (#.#.#.#)
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Network portion
Host portion
Special Addresses
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Network Address
Broadcast Address
Internet Protocol
Versn.
IHL Type of Svc.
Total Length
Identification
Flags
Fragment Offset
TTL
Protocol
Header Checksum
Source Address
Destination Address
Options
Padding
Data
ooo
IP Address Classes
Class
A
B
C
1st Byte
0 – 126
128 – 191
192 – 239
D
E
224 – 239
240 – 254
Format
Total Hosts
N.H.H.H 16 Million
N.N.H.H 64 Thousand
N.N.N.H 254
-
(Multicast)
(Experimental)
Hostnames
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Uniquely identifies each system
Fully Qualified Domain Name
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hostname.site.domain[.country]
Country: 2 letter identifier for country
Domain: Type of site (edu, com, org)
Site: Unique name of organization
Hostname: Unique name of system
DNS Name Resolution
Root Server
Non-Recursive
2
3
1
4
5
Recursive
8
host.domain.com
7
dns.domain.com
6
dns.iupui.edu
dns.cs.iupui.edu
Client-Server Model
Server
Client
Makes a request
Request fulfilled
Listens for
incoming
requests
Services
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TCP
TELNET, FTP, HTTP, NNTP,
SMTP, finger, talk, r-commands
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UDP
TFTP, NTP, SNMP NFS, DNS, RPC
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ICMP
ping, traceroute
Network Protocols
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Service request/response syntax
Often uses English commands
Request For Comments (RFC)
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Documentation for protocols and practices
Each revision its own number
May have a second classification
For Your Information (FYI)
 Best Common Practices (BCP)
 Standards (STD)
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Network Ports
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Enables processes to communicate with
each other across a network
64K possible ports
Privileged ports
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< 1024 reserved for system use only
Correspond to well-known services
Transmission Control Protocol
Source Port
Destination Port
Sequence Number
Acknowledgment Number
Offset Rsrvd.
Flags
Window
Checksum
Urgent Pointers
Options
Padding
Data
ooo
SYN 3-Way Handshake
SYN(C, ISNc)
SYN(S, ISNs) ACK(C, ISNc)
ACK(S, ISNs)
Client
Server
First step in all new TCP/IP sessions
User Datagram Protocol
Source Port
Length
Destination Port
Checksum
Data
ooo
“Connectionless”
Address Resolution Protocol
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Translates IP addresses to Ethernet (MAC)
addresses
Who is 10.0.0.3?
I am (1:2:3:7:8:9)
10.0.0.1
10.0.0.2
10.0.0.3
10.0.0.4
Ethernet Addressing
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Assigned by manufacturer (hardware)
Must be absolutely unique
Address format
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6 octets in hex (#:#:#:#:#:#)
First 3 octets: Manufacturer Identifier
Last 3 octets: Card serial number
Used for local network communication
Ethernet
Destination Address
Source Address
Data
Type
ooo
Data
Checksum
Interconnectivity
Application
Gateway
Transport
Application
Transport
Internet
Router
Internet
Network Access
Bridge
Network Access
Physical
Repeater
Physical
Routers
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Connects Networks together
If destination not on local network,
packets sent through gateway
Subnet Masks
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Splits networks into subnetworks
Separates address into 2 parts
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1’s – Network Portion
0’s – Host Portion
Example: Class C Network
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Address: N.N.N.H
Mask: 255.255.255.0 (255 = 11111111)
CIDR Notation: N.N.N.H/24