Networking Discussion Board
sb230529
CH11.pptxChapter 11 Networks of Networks
Chapter 11 Outline
Network topology
Basic internet structure and routing
Internet host addressing
Network inspection tools
Combining Computer Networks
Many early networks were Wide Area Networks or WANs
As LANs evolved, users wanted to connect LANs to WANs
Some connections had to span two or more WANs to reach from the desired source to the desired destination
Internet Protocol Stack
Routing Packets Between Networks
A node can move packets between LANs and/or WANs if it has a separate connection and MAC address on each network.
Every host connection also has a separate, unique Internet Protocol address (IP address)
Internet routing nodes (routers) use the IP address to direct the packet to its destination
Routing a Packet on Another LAN
Early Internet Security
The Internet evolved from the ARPANET
A research network developed by US DOD
Relied on physical security, a restricted user community, and limited applications for security
As the community grew, security relied on host based authentication (passwords)
Internet Worm and Wily Hacker promoted the development of Internet firewalls
Filtered traffic to try to block attacks
Computing versus Telecom Networks
Computing
Internet protocol suite (TCP/IP) is the prevailing standard
Designed around packets
Focus on reliable data transmission between computers
Telecom
SS7 – Signalling System 7 – is the prevailing standard
Designed around circuits
Focus on telephone and cell phone voice service
Evolution of Internet Structure
Connections Between Hosts
Socket interface – a popular network API
Provides basic send/receive functions
Basic client/server functions
Listen() – server awaits a connection
Accept() – server accepts a connection
Connect() – client requests a connection
Socket addresses – describe a process-to-process connection across the network
Socket Address Format
Contains pair of IP addresses and port numbers
Port number selects a client or server process
Sender Information
Source port number – chosen randomly by client
Source host's IP address
Recipient information
Destination port number – preassigned for well known Internet services
Destination host's IP address
Examples: Well-Known Port Numbers
21 – File transfer protocol: Sets up the transfer
22 – Secure shell protocol: Sends keyboard commands to a host
25 – Email forwarding protocol: Submits messages for delivery to another host
80 – World Wide Web: Retrieves web pages
IP Packet Addressing
IP Address Format
IP Packet Format
Address Resolution Protocol
“ARP” – looks up MAC or IP addresses on a LAN by asking other hosts for answers
Uses Ethernet “broadcast” feature
Asks “Who is 12.34.56.77?” for example
The hosts with answers send responses
Hosts save answers in their ARP cache
“arp” keyboard command prints the cache
ARP Packet Format
Routing and Addresses
Routing between hosts on a network may rely entirely on ARP
Connections depend on host addresses
To send packets to other networks, routers look at the network address within an IP address
The upper set of bits in the IP address represent the network address
The network mask indicates which bits are network address bits
Network Mask
Internet Addresses in Practice
Traditional IPv4 addresses are 32 bits long
Accommodate a few billion hosts
Addresses are scarce
New IPv6 addresses are larger but incompatible
Some networks use private addresses
These only work on the internal network
Must be converted to a public address to talk to Internet hosts on other networks
Use Network Address Translation (NAT)
Addressing and Scope
Addressing Scope Example
Network Inspection Tools
Wireshark
Can monitor network traffic in real time
Interprets frame and packet contents
Recognizes standard Internet protocols
Network gateway – lists devices on the LAN
nmap
Can “map” a network
Scans the network address range to locate hosts and the open ports on each host
Caution: May violate an ISP's use policy
Wireshark Main Window
© Wireshark Foundation
Wireshark: Ethernet Header
© Wireshark Foundation
Wireshark: ARP Request
© Wireshark Foundation
Wireshark: ARP Response
© Wireshark Foundation
Wireshark: IP Header
© Wireshark Foundation
Gateway List of Attached Devices
© Netgear
nmap: Scan A Host’s Services
