Comptia Network+ N10-006

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OSI Model

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Open Systems Interconnection Model is the primary architectural model for networks. It was created in the late 70's by the International Organization for Standardization (ISO).

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Application Layer

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Layer 7 of the OSI Reference Model that is in charge of file, print, message, database and application services.

Provides a user interface.

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Presentation Layer

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Layer 6 of the OSI Reference Model that is in charge of Data encryption, compression, and translation services.

Presents data and handles processing such as encryption.

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Session Layer

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Layer 5 of the OSI Reference Model that is in charge of Dialog Control.

Keeps different applications' data separate.

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Transport Layer

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Layer 4 of the OSI Reference model that is in charge of End-to-End connections.

Provides reliable or unreliable delivery and error correction before retransmit.

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Network Layer

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Layer 3 of the OSI Reference Model that is in charge of Routing.

Provides logical addressing which routers use for path determination.

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Data Link Layer

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Layer 2 of the OSI Reference Model that is in charge of Framing.

Combines packets into bytes and bytes into frames.

Provides access to media using the MAC address.

Performs error detection but not correction.

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Physical Layer

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Layer 1 of the OSI Reference Model that is in charge of the physical topology.

Moves bits between devices through cables.

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LAN

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Stands for Local Area Network

A data network that is restricted to a single geographical location and encompasses small areas such as an office building or school.

LAN's purpose is to interconnect workstation computers for sharing of files and resources.

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WAN

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Stands for Wide Area Network

A network that spans more than one geographic location, often connecting separated LANs.

Slower than LANs and more expensive due to adding routers, dedicated leased lines and implementation is more complicated.

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PAN

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Personal Area Network

A LAN created to share data among devices associated with you. AKA Wireless PAN (WPAN).

Connections are via Bluetooth, infrared or near-field communications (NFC).

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MAN

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Metropolitan-Area Network

A WAN confined to a certain geographic area such as a university campus or city.

Smaller than a WAN but bigger than a LAN.

Utilizes Internet Service Provider (ISP) or Telecommunications (Telco) provider.

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SCADA/ICS

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Supervisory Control and Data Acquisition/Industrial Control System

Communication between remote equipment of almost anything i.e.: pumping stations, robotic machines, etc.

A typical configuration includes an ICS server, Distributed Control System (DCS) devices creating a closed network, a remote terminal unit and a programmable logic controller.

Often used to analyze data from remote systems in real time.

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Medianets

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A Cisco architecture that can look at different types of media available and the application types and make a choice about which is the best combination to use.

Useful with Video Teleconferencing (VTC) and often used with Session Initiation Protocol (SIP)

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Network Models

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Peer-to-Peer and Client/Server

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Peer-to-Peer Network

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a network where all systems can share resources on their local computers as well as use resources from other systems.

Cheaper and easier to implement but doesn't work well with large numbers. Can have no more than 10 computers connected.

Can't backup files due to lack of centralized data storage.

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Client/Server Network

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A centralized network management model where a network administrator manages all network services including user management, security and backup procedures.

More expensive because it requires dedicated server hardware and software.

Most widely implemented model in real-world environments.

Client requests data from the server and presents that data to the users.

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Centralized vs Distributed Computing

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Centralized: one system provides both data storage and processing power for client systems. (i.e.: mainframes and dumb terminals)

Distributed: Process power is distributed between the client systems and the server.

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Topology

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A network's physical and logical layout.

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Bus Topology

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uses a trunk or backbone to connect all computers on the network. Uses T connectors or taps to connect systems. Each end of the physical bus must be terminated. No hub or switch is required.

Loose or missing terminators disrupt data transmissions. A break in the systems prevents all systems from accessing the network.

Uses IEEE 802.3 Ethernet standard.

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Ring Topology

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A logical ring meaning that the data travels in a circular fashion from one computer to another on a network. Also doesn't require a hub or switch.

If one system fails, the whole network fails.

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Star topology

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All computers and network devices connect to a central device called a hub or switch. Each connected device requires a single cable to be connected to a hub or switch creating a point-to-point connected between the device and hub or switch.

A single break in any cable doesn't cause the network to fail. However if the hub or switch fails the devices can't connect to the network.

Easy to troubleshoot and add or remove devices but more expensive to implement.

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Mesh Topology (Wired)

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incorporates a unique network design in which each computer on the network connects to every other, creating a point-to-point connection between every device on the network.

Purpose of mesh is to create a high level of redundancy.

One network cable fails, the data always has an alternative path to get to its destination.

Implementation is very complicated and troubleshooting is tricky.

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Hybrid Mesh Topology

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Creates a redundant point-to-point network connection between only specific network devices (such as the servers).

Most seen in WANs.

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Infrastructure Wireless Topology

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Used to extend a wired LAN to include wireless devices.

Wireless devices communicate with the wired LAN via an Access Point (AP) aka Wireless Access Point.

APs connect to the wired network.

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Ad Hoc Wireless Topology

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Devices communicate directly between themselves without an AP.

Connecting devices via Bluetooth is an example of an ad hoc network.

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Point-to-Point Network (PtP)

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A wireless network where the communication link travels from one node directly to another node.

Often used in wireless backbone systems such as microwave relay communications or as a replacement for a single wired communication cable.

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Wireless Bridge

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Used to connect two wired networks together over Wi-Fi.

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Point-to-Multipoint Network (PtMP)

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A wireless connection designed to link multiple wired networks.

Signals travel from a central node such as a base station of a cellular systems, an AP of a WLAN or a satellite.

Used in Wireless Internet Service Providers (WISPs), large corporate campuses, etc.

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Wireless LAN (WLAN)

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Wireless network that's dependent on a hotspot.

Coffee shops, train statins, restaurants or any public place uses hotspots.

Security is a concern and encryption should be used.

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Wireless Mesh Networks

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A wireless version of a Mesh topology. Each network node is connected to other nodes on the network.

Signal starts at a wireless base station (access point), attached to a wired network.

Extends the transmission distance by relaying the signal from one computer to another.

Cheaper than a wired mesh network.

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Wireless Mesh

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Created through the connection of wireless access points installed at each network user's locale.

Data signals in a wireless mesh rely on all nodes to propagate signals.

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Advantages of a Wireless Mesh

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Self-healing: ability to adapt to network failure and can function if a node is moved from one location to another. Possible due to wireless media and interconnected connections.

Scalable: Possible to add new systems to the network w/o cables.

Reliability: Due to the redundant number of paths for the data to travel ensures the data can reach its destination.

Cost: Self-configuring and doesn't needs cables. Can add, remove or relocate with little cost or disruption to the network.

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Hybrid Topology

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A combination of the star and bus topologies.

Can also refer to the combination of wired and wireless networks.

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Creating a SOHO Network

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1. List of requirements: Access to what

2. Device types/requirements: Cost

3. Environment limitations: If there's a wall that can block wireless connections.

4. Equipment limitations: number of ports on a network device.

5. Compatibility requirements: can they work well together?

6. Wired/Wireless considerations: Confirm if the area can go wireless.

7. Security considerations: Primary concern

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SOHO Network

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Stands for Small Office/Home Office Network

A network that serves 1 to 10 users in a small environment.

Consists of a SOHO router, and either a cable or DSL modem.

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Demarcation Point (Demarc)

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The point where the service provider stops being responsible for the line and it becomes your responsibility.

A box outside of a home or office located at the splitter nearest where the cable originates.

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Media Access Control (MAC) layer

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MAC address is defined at this layer. It's burned into the NIC card.

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Logical Link Control (LLC) layer

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Responsible for the error and flow-control mechanisms of the Data Link layer.

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Layer 1 protocols

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USB, Ethernet, DSL, ISDN, T-carrier links, GSM and SONET

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Layer 2 protocols

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High-Level Data Link Control (HDLC), Layer 2 Tunneling Protocol (L2TP), Point-to-Point Protocol (PPP), Point-to-Point Tunneling Protocol (PPTP), Spanning Tree Protocol (STP), & VLANs.

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Layer 3 protocols

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Routing Information Protocol (RIP), Open Shortest Path First (OSPF), Address Resolution Protocol (ARP), Reverse ARP (RARP), Asynchronous Transfer Mode (ATM), Intermediate System to Intermediate System (IS-IS), IP Security (IPsec) and Multiprotocol Layer Switching (MPLS)

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Transport Layer mechanisms

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Error checking ensures data is sent correctly

service addressing ensures data is passed to the right service

segmentation breaks data into packets for the lower levels to handle

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Layer 4 protocols

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User Datagram Protocol (UDP) connectionless

Transmission Control Protocol (TCP) connection-oriented

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Data Flow Control (Layer 4)

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How the receiving device accepts data in two ways:

Buffering: data is temporarily stored until destination device becomes available.

Windowing: data sent in groups of segments requiring only one acknowledgement.

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Layer 5 Protocols

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NetBIOS, Network File System (NFS) & Server Message Block (SMB)

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Dynamic Host Configuration Protocol (DHCP)

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enables ranges of IP addresses, known as scopes, to be defined on a server running a DHCP server application.

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Static addressing

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method of manually assigning an address from those available to you and allowing the host to always use that address.

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DHCP Process

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A system configured to use DHCP comes onto the network and broadcasts a special packet called DHCPDISCOVER to look for a DHCP server.

Server sees DHCPDISCOVER packet and picks it up. If it finds a scope for the network from which the packet originated, it chooses an address from the scope, reserves it and sends the address to the client in another packet called DHCPOFFER.

DHCPREQUEST packet notifies the server that the offer has been accepted after the selection process is completed.

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DHCP and DNS Suffixes

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suffixes define the DNS servers to be used and the order in which to use them. DHCP settings pushes a domain suffix search list to DNS clients.

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DHCP Relays

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an agent on the router that acts as a go-between for clients and the server. It makes the job of responding to requests easier.

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IP Helper

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Same as DHCP relay but by default will forward broadcasts for DHCP/BOOTP, TFTP, DNS, TACACS, the time service and the NetBIOS name/datagram service.

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Domain Name Service (DNS)

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Resolves hostnames to IP addresses

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Dynamic DNS (DDNS)

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A newer system that enables hosts to be dynamically registered with the DNS server.

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DNS Namespace

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Space that has logical divisions hierarchically organized such as .com, .gov, .uk, etc.

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Fully Qualified Domain Name (FQDN)

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includes all the components from the top of the DNS namespace to the host.

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Top-Level Domain Names

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com - Commercial Organizations

edu- Education Organizations

gov - US Government org

net - Network providers/centers

org - Non profit org

mil - Military

arpa - Reverse DNS lookup

de - country specific domain

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Reverse Lookup

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DNS performs IP address-to-hostname resolution using pointer (PTR) records.

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Types of DNS Entries

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A Record (address record) - maps a hostname to an IP address

MX - entries that correspond to mail exchanger systems

CNAME (Canonical Record) - creates alias records for a system.

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DNS Records

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Start of Authority (SOA) - A record of information containing data on DNS zones and other DNS records.

Name Server (NS): Stores information that identifies the name servers in the domain that store information for that domain.

Canonical Name (CNAME): Stores add'l hostnames or aliases for hosts in the domain.

Pointer (PTR): A pointer to the CNAME used to perform a reverse DNS lookup.

IPv6 Address (AAAA): Stores info for IPv6 addresses.

IPv4 Addresses (A): Stores info for IPv4 addresses.

Mail Exchange (MX): Stores info about there mail for the domain should be delivered.

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Windows Internet Name Service (WINS)

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a system on Windows networks used to enable NetBIOS names to be resolved to IP addressed.

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Simple Network Management Protocol (SNMP)

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enables network devices to communication information about their state to a central system.

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Components of SNMP

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Manager - a central system that acts as the central communication point for all SNMP-enabled devices on the network.

Agent - SNMP software configured with the manager's IP address to manage and monitor each device on the network.

Traps - Occurrences of certain events that the agent can communicate to the SNMP manager.

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SNMP Management Systems

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A computer running a special piece of software called a Network Management System (NMS). It allows you to monitor all the devices on a network.

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SNMP Agent

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any device that can run a small software component that facilitates communication with an SNMP manager.

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Management Information Bases (MIB)

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defines which parameters are accessible, which are read-only and which can be set.

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SNMP Communities

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Logical groupings of systems.

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SNMPv3

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The latest version of SNMP that supports authentication and encryption. Not available in the previous versions.

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Connection-Oriented Protocol

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Guarantees data delivery via the sending device re-sending any packet that the destination device doesn't receive.

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Connectionless Protocol

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Offers only a best effort delivery mechanism. Information is sent, but the sending device doesn't receive confirmation that it was received. These are popular in applications for streaming audio and video.

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Internet Protocol (IP)

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Used to transport data from one node on a network to another. It's a connectionless protocol that operates at Layer 3.

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Transmission Control Protocol (TCP)

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A Layer 4, connection-oriented protocol. It uses the 3-handed handshake where it sends a message called a SYN to the target host. Target host then opens a connection for the request then sends back an acknowledgement message called an ACK. The originating host then sends another ACK saying the ACK has been received and the session is ready to be used to transfer data.

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User Datagram Protocol (UDP)

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A fire-and-forget protocol that assumes the data sent will reach its destination.

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File Transfer Protocol (FTP)

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Provides for the uploading and downloading of files from a remote host running FTP server software. A Layer 7 protocol. Operates on Ports 20 & 21.

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Secure FTP (SFTP)

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Based on secured-shell (SSH) technology that provides robust authentication between sender & receiver, and encryption.

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Trivial FTP (TFTP)

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Associated with simple downloads. A Layer 7 protocol that uses UDP. Port 69

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Simple Mail Transfer Protocol (SMTP)

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Defines how mail messages are sent between hosts. Uses TCP. Port 25.

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Hypertext Transfer Protocol (HTTP)

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Protocol that enables text, graphics, multimedia and other material to be downloaded from an HTTP server. It uses an Uniform Resource Locator (URL) to determine what page should be downloaded from the remote server. Uses Port 80.

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Secure HTTP (SHTTP)

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Uses Secure Sockets Layer (SSL) which encrypts information sent between client & host. Uses Port 443.

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Post Office Protocol version 3(POP3)/Internet Message Access Protocol version 4(IMAP 4)

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Mechanisms for downloading, or pulling email from a server. Difference between the two is POP3 transmits passwords in clear text where IMAP uses an authentication system which makes it difficult to determine a password. Ports: POP3 - 110, IMAP - 143.

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Telnet

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A virtual terminal protocol that enables sessions to be opened on a remote host. Port 23.

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Secure Shell (SSH)

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A secure alternative to Telnet which encrypts data as it travels between systems. Port 22.

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Internet Control Message Protocol (ICMP)

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Works with the IP layer to provide error checking and reporting functionality.

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Address Resolution Protocol (ARP)/Reverse ARP (RARP)

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ARP - Resolves IP addresses to MAC addresses.

RARP - Resolves MAC addresses to IP addresses.

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Network Time Protocol (NTP)

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Facilitates communication of time between systems. Port 123.

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Network News Transfer Protocol (NNTP)

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Posts and retrieves messages from news groups. Port 119.

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Secure Copy Protocol (SCP)

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Provides a secure means to copy files between systems on a network.

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Lightweight Directory Access Protocol (LDAP)

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Provides a mechanism to access query directory service systems.

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Internet Group Management Protocol (IGMP)

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Part of the TCP/IP Suite - Manages multicast groups.

Multicasting: groups of network devices who are able to send and receive data between the members of a group at one time.

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Transport Layer Security (TLS)

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A security protocol designed to ensure privacy between communicating client/server applications. Two Layers of TLS:

TLS Record - Ensures connection made is private using encryption.

TLS Handshake - Used for authentication between client & server.

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Voice over Internet Protocol (VoIP)

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Enables regular voice conversations to occur by traveling through IP packets and via the Internet.

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Session Initiation Protocol (SIP)

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Layer 7 protocol designed to establish and maintain multimedia sessions for audio/video conferencing, online gaming & person-to-person communication over the Internet. Uses TCP or UDP. Port 5060 & 5061.

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Real-Time Transport Protocol (RTP)

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Transports real-time data including audio and video. Ports 5004 and 5005.

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Remote Desktop Protocol (RDP)

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Used in Windows for remote connections. Port 3389.

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Server Message Block (SMB)

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Used on network for providing access to resources. Port 445.