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Ethernet & TCP/IP Networking_2 (TCP/IP addressing -port addresses…
Ethernet & TCP/IP Networking_2
TCP/IP addressing
-port addresses (port numbers)
example: port 80 is commonly used for Web services
First 1024 numbers are called well-known ports because they are standard addresses specified for most common applications
16 bits in length
User defined port numbers are also available to applications
Transport layer uses these addresses to identify the application that is to receive the message
eg, the following web service uses the
user-defined port
of 8080:
http://www.somewhere.org:8080/hiddenServer
Well-known port numbers
Sockets
Provide an interface btwn the application layer & the transport layer to initiate connections & send messages through the network
Defined by source port number & IP
Originated with BSD UNIX
Allows for multiple simultaneous open connections
Transport Layer Protocols
UDP
(User Datagram Protocol)
Unreliable, connectionless service
No acknowledgement of receipt by receiving node
Eg: streaming video
SCTP
(Stream Control Transmission Protocol)
Similar to TCP but with improved fault tolerance & ability to transport multiple messages through the same connection
TCP
(Transmission Control Protocol)
Control packets are used to create a full
duplex logical connection through
handshaking
Numbering of packets allows packets to
be reassembled in order
Connection-oriented, reliable delivery service
IPv4 addresses
Assigned in blocks of contiguous addresses
-no of addresses is power of two
-eg: 208.80.152.2 (Wiki IP address)
Divided into 3 levels
-network address
-subnetworks (subnets)
-Hosts (nodes)
32 bits long divided into 4 octets
Masks
-used to separate the different parts of the address
Registered & allocated by ICANN
IPv6
128-bit addresses arranged as 8 groups of 4-digit hexadecimal numbers separated by colons
Leading zeros & zero values in one or
more consecutive groups may be eliminated
IPv6 protocol is intended to eventually
replace IPv4 to provide additional IP addresses
eg
NAT & DHCP
-two methods to distribute
IP addresses more efficiently
Network Address Translation (NAT)
The router must re-address traffic passing
btwn the internet & the local network
Difficult with large networks
Use of private network
IP addresses behind a router
Dynamic Host Configuration Protocol (DHCP)
Method often used by large
organisations, DSL, & cable providers
DHCP client on computer or network device
broadcasts a query to locate the DHCP server
Maintain a bank of available IP
addresses & assign them dynamically
to computers for use when the computers
are attached to the network
DHCP server responds with a lease that includes
an IP address, domain name of network,
IP address of DNS server, subnet mask,
IP address of gateway, & other configuration parameters
Network Security Categories
Authentication
verifying the identity of a source of data being received
Data integrity & non-repudiation
protecting the content of data communication against changes & verifying the source of the message
Confidentiality
Keeping the content of data private
Assuring network availability & access control
keep network resources operational & restricting access to those permitted to use them
Intrusion
keeping network & system resources free from intruders
Domain names & DNS services
Domain names
Hierarchical system of network address identifiers used throughout the internet & on LANs, intranets & extranets
Created so users would not have to memorise IP addresses
Domain Name System (DNS)
Uses a massive distributed database
containing a directory system of servers
Each entry contains a domain name
& an associated IP address
Domain name resolution - translates
domain names into IP addresses
Network Security
Physical & logical
access restriction
firewall
Private networks
limit access to wiring & network equipment
Encryption
Symmetric key cryptography
both keys used for encryption & decryption
both sender & receiver use the same key, which makes security difficult
Public key-private key cryptography
two different keys are used for encryption & decryption
Network intrusions
packet sniffers read data in a packet as it passes through a network
probing attacks to uncover IP address/port no's that accept data packets