Layer 1 (OSI Model)
Physical layer.
Signaling, Cabling, Connectors.
(Ex: Cable, Network Interface Card, Hub)
Layer 2 (OSI Model)
Data Link layer.
The Switching Layer
(Ex: Frame, MAC Address, EUI-48, EUI-64, Switch)
Layer 3 (OSI Model)
Network layer.
The Routing Layer
(Ex: IP Address, Router, Packet)
Layer 4 (OSI Model)
Transport layer.
The "Post Office" Layer
(Ex: TCP Segment, UDP Datagram)
Layer 5 (OSI Model)
Session layer.
Communication between devices
(Ex: Control Protocols, Tunneling Protocols)
Layer 6 (OSI Model)
Presentation layer.
Encoding/Encryption
(Ex: SSL/TLS)
Layer 7 (OSI Model)
Application layer.
Layer We See
(Ex: Gmail, Twitter, Facebook)
Network Interface/ Link Layer (TCP/IP Model)
Data Link Layer
Physical Layer
Internet Layer (TCP/IP Model)
Network Layer
Transport (TCP/IP Model)
Transport Layer
Application Layer (TCP/IP Model)
Application Layer.
Presentation Layer.
Session Layer.
Class A IP Address
1-126 Leading bits.
128 Networks.
16,777,214 Hosts per Network.
Default Subnet Mask 255.0.0.0
Class B IP Address
128-191 Leading bits.
16,384 Networks.
65,534 Hosts per Network.
Default Subnet Mask 255.255.0.0
Class C IP Address
192-223 Leading bits.
2,097,152 Networks.
254 Hosts per Network.
Default Subnet Mask 255.255.255.0
Class D (Multicast) IP Address
224-239 Leading bits
Class E (Reserved) IP Address
240-254 Leading bits
MAC Address
Media Access Control.
Uniquely identifies a host on a network.
Burned into Network Interface.
Multicast
Single packet transmission from one sender to a specific group of destination nodes
Unicast
Communication that takes place over a network between a single sender and single receiver
Broadcast
Packet Delivery system which a copy of a packet is transmitted to ALL hosts attached to the network
APIPA
Automatic Private IP Addressing.
Technology implemented on certain Windows Platforms.
System assigns itself an IP address in the absence of a DHCP server.
Addresses assigned from 169.254.x.x Address Range.
EIGRP
Enhanced Interior Gateway Routing Protocol.
Routers configured to use EIGRP keep copies of their neighbors' routing information and query these tables to help find the best possible route for transmissions to follow
OSPF
Open Shortest Path First.
A Link-State routing protocol used on TCP/IP networks
RIP
Routing Information Protocol.
Uses hop count as a routing metric to control the direction and flow of packets between routers on an internet network
Link State Routing
Dynamic routing method in which routers tell neighboring routers of their existence through packets called Link State Advertisements (LSAs). By interpreting the information in these packets, routers can create maps of the entire network
Distance Vector Routing
Type of routing in which a router uses broadcasts to inform neighboring routers on the network of the routes it knows about
Hybrid Routing
Routing protocol that uses the attributes of both distance vector and link state
Static Routing
Routing method in which all routes must be entered into a device manually an in which NO route information is exchanged between routing devices on the network
Dynamic Routing
Routing system that enables routing information to be communicated between devices automatically and can recognize changes in the network topology and update routing tables accordingly
Hop Count (Routing Metric)
Refers to the number of router nodes that a packet must pass through to reach its destination
MTU, Bandwidth (Routing Metric)
Maximum Transmission Unit.
size in bytes of the largest protocol data unit that the layer can pass onward
Bandwidth correlates to the amount of data that can traverse the medium at one time
Costs (Routing Metric)
Value used to encourage/discourage the use of a certain route through a network.
Discouraged routes are assigned a higher cost.
Encouraged routes are assigned a lower cost.
Latency (Routing Metric)
The delay induced by a piece of equipment or device used to transfer data
Next Hop
Next closest router that a packet can go through
Spanning-Tree Protocol (STP)
Prevents loops on a switched network.
When a network topology changes occurs, STP automatically adjusts to the change.
Switches communicate using BPDUs (Bridge Protocol Data Units)
VLAN 802.1q
Virtual LAN.
This enables devices to operate as if they were connected to the same physical, regardless of whether they are connected to the same switch
Port Mirroring
Process by which two ports on a device are configured to receive the same information.
Helpful in troubleshooting scenarios.
Broadcast Domain
Layer 2 of the OSI Model.
A switch creates an entire broadcast domain (provided that there's only one VLAN) since broadcasts are a layer 2 concept (mac address related)
Collision Domain
Layer 1 of the OSI Model.
A hub is an entire collision domain since it forwards every bit it receives from one interface on every other interfaces
IGP
Interior Gateway Protocol.
Identifies the protocols used to exchange routing information between routers within LAN or interconnected LAN's.
EGP
Exterior Gateway Protocol.
Defines distance vector protocols commonly used between host on the Internet to exchange routing table information.
Routing Tables
Database in a router that stores and updates the locations (addresses) of other network devices and the most efficient routes to them.
Used to direct Routing.
Convergence (Steady State)
When all routers/devices are at the same information level.
SMTP
Simple Mail Transfer Protocol.
Port 25
Internet protocol used for the transfer of email messages and attachments.
HTTP
Hypertext Transfer Protocol.
Port 80
Protocol used by web browsers to transfer pages, links, and graphics from the remote node to the users computer.
HTTPS
Hypertext Transfer Protocol Secure.
Port 443
Performs the same function as HTTP but does so over an encrypted link.
FTP
File Transfer Protocol.
Port 20, 21
Protocol that provides for the transfer of files between two systems.
Operates at Layer 7 of the OSI Model.
Telnet
Telnet
Port 23
A standard terminal emulation protocol in the TCP/IP Stack.
Used to perform terminal emulation over TCP/IP via Remote Terminal connections.
IMAP
Internet Message Access Protocol.
Port 143
RDP
Remote Desktop Protocol.
Port 3389
SSH
Secure Shell
Port 22
Enables a session to be open on a remote host.
Differs from Telnet because it provides additional authentication methods and encryption for data as it traverses the network.
DNS
Domain Name Service/Server/System.
Port 53
System used to translate domain names into IP addresses.
DHCP
Dynamic Host Configuration Protocol.
Port 67, 68
Provides dynamic IP addressing to DHCP enabled workstations on the network
TCP
Transmission Control Protocol.
Connection-oriented.
RELIABLE data transmission communication service.
Operates at the Transport layer of the OSI model.
UDP
User Datagram Protocol.
Connectionless.
UNRELIABLE communication services.
Operates at the Transport layer of the OSI model.
TCP/IP Suite
Transmission Control Protocol/ Internet Protocol.
Originally designed for use on large internetworks but has now become the de facto protocol for networks of all sizes.
TFTP
Trivial File Transfer Protocol.
Port 69
Simplified version on FTP that enables file transfers but doesn't offer any security or file management capabilities
ARP
Address Resolution Protocol.
Used to resolve IP addresses to MAC addresses.
ARP command returns a Layer 2 address for a Layer 3 address.
SIP (VoIP)
Session Initiation Protocol.
Application Layer protocol designed to establish and maintain multimedia sessions such as Internet telephony calls.
RTP (VoIP)
Real Time Protocol.
Internet standard protocol for the transport of real-time data, including audio and video.
POP3
Post Office Protocol version 3.
Used to retrieve mail stored on a remote server.
Application Layer protocol.
NTP
Network Time Protocol.
Port 123
Protocol used to communicate time synchronization information between devices on the network.
IMAP4
Internet Message Access Protocol version 4.
Protocol that enables email to be retrieved from a remote server.
Offers more functionality than POP3.
SNMP
Simple Network Management Protocol.
Provides network devices with a method to monitor and control network devices; Manage Configurations, statistics collection, performance, and security.
Reports network management information to a management console.
ICMP
Internet Control Message Protocol.
Network Layer Internet protocol documented in RFC 792.
Reports errors and provides other information relevant to IP packet processing.
Utilities such as Ping and Tracert use functionality provided by ICMP.
IGMP
Internet Group Message Protocol.
Protocol used for communication between devices within the same multicast group.
Provides a mechanism for systems to detect and make themselves aware of other systems in the same group.
TLS
Transport Layer Security.
Security Protocol designed to ensure privacy between communicating client/server applications.
TLS ensures that no one can eavesdrop and intercept/tamper with the data message.
**
TLS is the successor to SSL.
**
DNS Servers
Servers that translate specific domain names into IP addresses so that data may be routed.
A (DNS Records)
Address Mapping records.
Specifies IP address (IPv4) for given host.
A records are used for conversion of domain names to corresponding addresses.
MX (DNS Records)
Mail Exchange.
Stores information about where mail for the domain should be delivered.
AAAA (DNS Records)
IPv6 Address.
Stores information for IPv6 (128 bit) addresses.
Most commonly used to map hostname to an IP address for a host.
CNAME (DNS Records)
Canonical Name.
Specifies an alias/nickname for a canonical hostname record in a DNS database.
Used to give a single computer multiple names/aliases.
PTR (DNS Records)
Pointer.
Used to perform a reverse DNS lookup, in which case the name is returned when the query originates with an IP address.
Dynamic DNS (DDNS)
Dynamic Domain Name Service.
Form of DNS that enables systems to be registered and de-registered with DNS dynamically.
Facilitated by DHCP, which passes IP address assignments to the DNS server for entry into DNS server records.
Network Troubleshooting Methodology
Identify the problem.
Establish theory of probable cause.
Test the Theory to determine cause.
Establish plan of action to resolve the problem and identify potential effects.
Implement the solution or escalate as necessary.
Verify full system functionality
Virtual Switches
Works the same as physical switch but allows multiple switches to exist on the same host (saving the implementation of additional hardware).
Regularly used with VLAN implementations.
Virtual Desktops
Virtual system running on a computer to allow multiple operating systems to run.
Often called Virtual Desktop Interface (VDI).
Virtual Servers
Allows a single physical server to act as multiple server.
A single server can host multiple logical machines.
Virtual PBX
Virtual Private Branch Exchange.
Phone system that handles such features as call routing, voicemail, faxing, etc.
Cost-savings method that incorporates VoIP.
NaaS
Network as a Service.
Similar to offsite virtual network in that the server and desktop are all virtualized and managed by a contracted third-part.