Midterm 1 - CECS 303

IEEE

An international society of engineering professionals whose goal is to promote development and education in electrical engineering and computer science fields.

IEEE Project 802

Effort to standardize physical and logical network elements.

802.3

Ethernet

802.11

Wireless

ISO (International Organization for Standardization)

Organization whose goal is to establish technological standards to facilitate global information exchange and barrier free trade.

ITU (International Telecommunication Union)

global telecommunication issues and worldwide internet services implementation

ISOC (Internet Society)

supports growth of the internet. Establishes technical internet standards.

IP (Internet Protocol) address

An address identifying computers in TCP/IP (Internet) based networks. Network Layer Protocol.

IANA (Internet Assigned Numbers Authority)

Assigns IP addresses. Was split up into three regional registries

ARIN

American Internet Registry

APNIC

Asia Pacific Internet Registry

RIPE

European Internet Registry

OSI Model

Model for understanding and developing host to host commections

PDUS (protocol data units)

Discrete amounts of data. Flows through layers 6, 5, 4, 3, 2, 1.

Type of PDUS in Layers 5-7

data

Type of PDUS in Layer 4

Segment

Type of PDUS in Layer 3

Packet

Type of PDUS in Layer 2

Frame

Type of PDUS in Layer 1

Bits

Application layer

does not include the software apps, facilitates communication between software apps and lower layer network services. EX: HTTP

Presentation Layer

accepts application layer data. Formats data that is understandable to different applications and hosts. EX of files translated: GIF, JPG, MPEG. Manages data encryption and decryption (SSL)

Session Layer

Coordinate and maintain communication between two network nodes (keeping alive communications throughout the session). Helps keep communications secure, synchronized dialogue, etc.)

Transport Layer

Accepts data from the sessions layer. Manages end to end data delivery. Handles flow control.

TCP Handshake

Connection Oriented Protocol. SYN -> SYN-ACK -> ACK. Has a checksum for data integrity.

UDP

Connectionless protocol. Does not establish a connection, does not check for data integrity BUT much faster.

Segmentation

Breaks large data units received from the session layer into smaller units called segments. Increases data transmission efficiency.

Network Layer

Translates network addresses into physical counterparts. Decides how to route data from sender to receiver. Know addressing and routing. Linked to firewalls. EX. Routers

Addressing

A system for assigning unique identification numbers to network devices.

Network Address

logical or virtual, EX 192.168.1.4

Physical Address

MAC. A fixed number associated with each device’s network interface EX. A6-2B-B5-AE-00-FB (48 bits)

Factors to determine path routing

delivery priority, network congestion, quality of service, cost of alternative routes.

Fragmentation

subdividing transport layer segments

Data Link Layer

Divides data received into distinct frames for transmission in Physical layer. Uses Frames

Frame

structured package for moving data. Includes raw data payload, sender and receiver network addresses, and error checking and control information. Not all info is received, corrected by error checking. Checks for errors by frame check sequence and cyclic redundancy check

LLC (Logical Link Control)

sublayer of the datalink layer

MAC (Media Access Control)

sublayer of the datalink layer. manages access to the physical medium, and appends the physical address of the destination computer onto data frame

Physical Layer

accepts frames from the data link layer. Generate signals as changes in voltage at the NIC.

Copper

signals issues as voltage

Fiber-optic

signals issued as light pulse

Wireless

signals issued as electromagnetic waves

Computer network

A group of interconnected computers and devices. Connected by transmission media. ADVANTAGES -> device and resource sharing by multiple users. Central network management.

Peer to Peer

direct computer communication, equal authority, individual resource sharing (up to individuals if resources are shared). Advantages-> simple config, less expensive. Disadvantages-> not flexible, less secure, not practical for large installations / businesses. Resources shared by modifying file sharing controls (user controlled). Not centrally controlled (access not uniform or secure). EX: Napster, Bittorrent

Server

central computer, facilitates communication and resource sharing. RESPONSIBILITIES -> manage client data/resources, authenticate access, control file access, restrict user network access, dictate computer communication rules, supply applications to clients. OS EXAMPLES -> unix, linux, Microsoft server, macOS Server. Compared to clients, has increased memory, processing, storage plus probably has special hardware.

Clients

personal computers, mobile devices, IoT

LAN (local area network)

Network confined to a small location. Currently used for large complex client/server networks and P2P networks

MAN (metropolitan area network)

Connects clients and server from multiple buildings. EX: CSULB

WAN (Wide area network)

Connects two or more geographically separate LANS or MANS. Often connected via the internet and different internet service providers.

Common Network Uses

File and Print Services, Access Services, Mail Servers

Internet Protocol

Determines how and where data is delivered, including data’s source and destination address. Enables TCP/IP to internetwork. Contains network layer data formed into packets.

IP packet

data envelope containing information for routers to transfer data between different LAN segments

IPv4

IP version that is unreliable and has connectionless protocol

IPv6

IP version that has connectionless and connection-oriented protocol. Was created because more IP addresses were needed.

ARP (Address Resolution Protocol)

Network layer protcol used with IPv4. Contains MAC (physical) address of a host or node. Creates a database mapping MAC addresses to IP addresses.

ARP Table

Table of recognized MAC-to-IP address mappings, stored locally on network devices, increases efficiency. Contains dynamic and static entries

ICMP (Internet Control Message Protocol)

Network layer protocol reporting on data delivery success or failure. Announces transmission failures to the sender. cannot correct errors, but provides critical network troubleshooting information

Class A IPv4

0-127 First Octet, 0.0.0.0 - 127.255.255.255. Subnet Mask 255.0.0.0

Class B

128-191 First Octet. 128.0.0.0-191.255.255.255. Subnet Mask 255.255.0.0

Class C IPv4

192-233 First Octet, 192.0.0.0- 223.255.255.255, Subnet Mask 255.255.255.0

Class D IPv4

Multicast. 224-239 First Octet, 224.0.0.0.0- 239.255.255.255

Class E

Experiemental. 240-255 First Octet. 240.0.0.0- 255.255.255.255

What is the first octet of the loopback address?

127 (127.0.0.1), used for loopback tests.

What is a loopback test used for?

Attempting to connect to your own machine, useful for troubleshooting

ifconfig

command used for loopback tests on Linux/Unix and Windows

dotted decimal notation

Common way of expressing IP addresses, each octet is a decimal number between 0 and 255 separated by periods.

subnet mask

A 32-bit number identifying a device’s subnet, used to inform the network about the logical subdivision of IPs.

How is a subnet mask formatted?

Four octets (32 bits), expressed in binary or dotted decimal notation.

How many bits does an IPv6 address have?

28 bits, composed of eight 16-bit fields.

How do most companies and individuals obtain IP addresses?

From ISPs.

What is a static IP address?

An IP address that is manually assigned.

What is a dynamic IP address?

An IP address that is assigned automatically via DHCP.

DHCP

Automatically assigns a unique IP address.

DHCP leasing process

The device borrows an IP address while attached to the network.

What determines the lease time in DHCP?

It is determined when the client logs on.

When may a DHCP lease be terminated?

A user may force lease termination, and it can be manually terminated due to server failure, network troubleshooting, or another client needing the IP address.

What do hosts within an organization use private addresses for?

Internal communication, not routed on public networks.

Socket

A combination of a port number and a host machine’s IP address.

Well Known ports

0 to 1023

Registered Ports

1024 to 49151

Dynamic/private ports

49152 to 65535

Why are domain names used instead of IP addresses?

Because IP addresses are long and complex, so domain names are used for easier human interaction.

domain name

A group of computers belonging to the same organization (e.g., abc.com).

DNS

Associates domain names with IP addresses.

What are the three types of DNS servers?

Resolvers, authoritative name servers, and root servers.

recursive DNS query

The resolver responds directly to a client with a top-down search.

iterative DNS query

The resolver provides a direct answer if known or refers the client to another server.

non-recursive DNS query

The resolver has the answer cached.

DDNS

Automatically updates DNS records when IP addresses change.

Who typically uses DDNS?

Small businesses or individuals with dynamic external IP addresses.

How can external LAN security breaches be prevented?

By restricting access at every point where the LAN connects to the rest of the world.

Router Access List

Controls traffic through routers

router’s main functions

Examine packets and determine the destination based on Network layer addressing information.

ACL (access control list)

routers can decline to forward certain packets.

Stateless ACL

Access lists look at packets independently of previous traffic.

Stateful ACL

Allow traffic implicitly based on previous traffic.

What variables do ACLs use to permit or deny traffic?

Network layer protocol, transport layer protocol, source IP address, source netmask, destination IP address, destination netmask, TCP or UDP port number.

What happens when a router receives a packet?

The router examines the packet and refers to the ACL for permit/deny criteria. It drops the packet if deny characteristics match or forwards it if permit characteristics match.

firewall

A specialized device or computer installed with specialized software that selectively filters and blocks traffic between networks.

What are the locations of firewalls?

Between two interconnected private networks, between a private network and a public network (network-based firewall), and between two hosts (host-based firewall).

What is the most common form of firewall?

Packet filters

stateful packet filter

Makes decisions based on previous traffic, such as allowing return traffic from a web server.