CompTia Network+ N10-007

text (TXT) record

The text (TXT) records contain human-readable text, and are designed to help with fraudulent phishing emails. The Sender Policy Framework (SPF) record within the TXT record helps filter out emails that are spoofed to appear as if they are coming from your domain. SPF looks at the IP address of the last SMTP server and verifies that the IP address and SMTP server match. Domain Keys Identified Mail (DKIM) validates that an email sent from a domain was authorized by the owner of the domain.

Bring Your Own Device (BYOD)

An explicit and detailed list of what devices are actually permitted An explicit security policy for each device or device category The appropriate corporate support policy for each device or device category A clear delineation of what applications and data are owned by the corporation versus that owned by the user and/or employee An explicit list of applications permitted in the BYOD environment An integration of the BYOD policy with the acceptable use policy (AUP, covered next) A detailed presentation of the exit policies for employees as they relate to BYOD

Link Aggregation

As defined by the IEEE 802.3ad standard, link aggregation allows multiple physical connections to be logically bundled into a single logical connection.

wireless analyzer

Can identify problems such as signal loss, overlapping or mismatched channels, unacceptable signal-to-noise ratios, rogue APs, and power levels.

Crossover Cable Diagram

Computers can connect to the network through a hub or switch with a straight-through cable. Computers, switch-to-hub, and router-to-PC also connect directly to one another using a crossover cable.

Layer 2 loop

Data Link Layer Troubleshooting: STP might be functioning suboptimally, because a root bridge was automatically selected rather than being specified, resulting in a suboptimal path. So, you should be able to examine your Ethernet switches, when troubleshooting, and determine the STP roles of your network's switches and switch ports. Two problems that could result in a Layer 2 loop are MAC table corruption and broadcast storms.

examples of network-attached storage (NAS)

IP Small Computer System Interface (iSCSI), Fibre Channel, and Network File System (NFS). Some networks are purpose-built for the communications between a server and its disk storage

The protocols and devices in a VoIP

IP phone: A telephone with an integrated Ethernet connection Call agent: A repository for a VoIP network's dial plan Gateway: Acts as a translator between two different telephony signaling environments SIP (Session Initiation Protocol): The Layer 4 protocol that carries voice

hub-and-spoke

In a hub-and-spoke topology, each remote site connects back to a main site via a WAN link. lacks redundancy because each remote site is reachable by only a single WAN link. adding additional sites is easy as compared to a partial-mesh topology.

Dedicated Leased Line

Leased lines are actually reserved circuits within the service provider's network that connect geographically separated offices for private voice and/or data networking. The circuits are typically rented at a monthly or yearly rate. They can be expensive.

Multicast

Messages are sent to a specific group of hosts on the network

Multiplexing Strategy

Multiplexing allows multiple communications sessions to share the same physical medium. Cable TV, allows you to receive multiple channels over a single physical medium (for example, a coaxial cable plugged into the back of your television). Here are some of the more common approaches to multiplexing: Time-division multiplexing (TDM): TDM supports different communication sessions (for example, different telephone conversations in a telephony network) on the same physical medium by causing the sessions to take turns. For a brief period, defined as a time slot, data from the first session is sent, followed by data from the second session. This continues until all sessions have had a turn, and the process repeats itself. Statistical time-division multiplexing (StatTDM): A downside to TDM is that each communication session receives its own time slot, even if one of the sessions does not have any data to send at the moment. To make a more efficient use of available bandwidth, StatTDM dynamically assigns time slots to communications sessions on an as-needed basis. Frequency-division multiplexing (FDM): FDM divides a medium's frequency range into channels, and different communication sessions send their data over different channels. As previously described, this approach to bandwidth usage is called broadband.

NAT IP addresses

NAT allows private IP addresses to be translated into Internet-routable IP addresses. Address translation can also be done for specific ports associated with an IP address. When this is done, it's often referred to as port forwarding. Inside local: A private IP address referencing an inside device Inside global: A public IP address referencing an inside device Outside local: A private IP address referencing an outside device Outside global: A public IP address referencing an outside device As a memory aid, remember that inside always refers to an inside device (source), and outside always refers to an outside device (destination). Also, think of the word local being similar to the Spanish word loco, meaning crazy. That is what a local address could be thought of. It is a crazy, made-up address (a private IP address that is not routable on the Internet). Finally, let the g in global remind you of the g in good, because a global address is a good (routable on the Internet) IP address.

TCP/IP Layers

Network interface: This layer encompasses the technologies addressed by Layers 1 and 2 (physical and data link layers) of the OSI model. The Network interface layer defines how data is physically sent through the network. Internet: This layer maps to Layer 3 (the network layer) of the OSI model. The Internet layer performs IP routing. Transport: This layer maps to Layer 4 (the transport layer) of the OSI model. The Transport layer manages communication sessions between host computers. Application: This layer addresses concepts described by Layers 5, 6, and 7 (the session, presentation, and application layers) of the OSI model. The Application layer defines how host programs interface with the transport layer services to use the network.

Opens and shorts

Physical Layer Troubleshooting: An open is a broken strand of copper, preventing current from flowing through a circuit. However, a short occurs when two copper connectors touch each other, resulting in current flowing through that short rather than the attached electrical circuit because the short has lower resistance.

Splitting pairs in a cable

Physical Layer Troubleshooting: An unshielded twisted-pair (UTP) cable consists of eight separate copper leads. However, only four of those eight leads are used for data (two transmit leads and two receive leads). This results in four unused leads. Some installers use those four extra leads to support a second Ethernet connection on a single UTP cable. Although such an approach can function, nonstandard wires are being used for connecting the second Ethernet connection. Therefore, you should be aware of any nonstandard pinouts used in the network that you are troubleshooting.

Cable placement

Physical Layer Troubleshooting: Because copper cables are subject to electromagnetic interference (EMI), you should arrange cables to minimize interference. Ideally, Ethernet cables should not be placed in close proximity with high-voltage cables, generators, motors, or radio transmitters. For example, when running cables between buildings via underground conduit, you should ideally place network cabling in a conduit separate from the electrical cables.

Crosstalk

Physical Layer Troubleshooting: Crosstalk can occur when an analog connection creates an electromagnetic field around its conductors, inducing its waveforms on a nearby analog connection. This phenomenon is most commonly experienced in an analog phone call. Crosstalk can be minimized by using a higher category of cabling because higher categories of cables better limit the radiation of electromagnetic waves.

Bad cables or connectors

Physical Layer Troubleshooting: Faulty cables or faulty connectors can prevent successful data transmission at Layer 1. A bad cable could simply be an incorrect category of cable being used for a specific purpose. For example, perhaps you interconnected two 1000BASE-TX devices using a Cat 5 cable (instead of a Cat 6 or higher cable), resulting in corrupted data. Bent pins in a connector or incorrect pinouts could also be the issue.

Transposed Tx/Rx leads

Physical Layer Troubleshooting: Some Ethernet switches support medium dependent interface crossover (MDIX), which allows a switch port to properly configure its leads as transmit (Tx) or receive (Rx) leads. You can interconnect such switches with a straight-through cable (as opposed to a crossover cable). However, if a network device does not support MDIX, it needs an appropriate cable (that is, a crossover cable) to allow its Tx leads to connect to the Rx leads on a connected device, and vice versa. Therefore, care must be taken when selecting cable types interconnecting network components.

Speed/duplex mismatch

Physical Layer Troubleshooting: Speed and duplex mismatches can be tricky to troubleshoot in the network, especially considering that connectivity is often maintained, just at unacceptable levels.

decibel loss (dB loss)

Physical Layer Troubleshooting: The signal power of a data transmission might be degraded to the point where the transmission is not correctly interpreted by a receiving device. This loss of signal power, called a decibel loss (dB loss), could result from exceeding the distance limitation of a copper or fiber cable.

Transceiver mismatch

Physical Layer Troubleshooting: Transceivers must be selected carefully to ensure compatibility with the cable type and wavelengths in use.

Symmetric Encryption

Symmetric encryption is fast in comparison to asymmetric encryption. Examples of symmetric encryption algorithms include the following: DES: Data Encryption Standard (DES) is an older encryption algorithm using a 56-bit key. It is considered weak by today's standards. 3DES: Triple DES (3DES), uses three 56-bit DES keys (for a total of 168 bits) and is usually considered a strong encryption algorithm. However, the security of 3DES varies based on the way it is implemented. Specifically, 3DES has three keying options, where all three keys are different (keying option 1), two of the three keys are the same (keying option 2), or all three keys are the same (keying option 3) to maintain backward compatibility with DES. AES: Advanced Encryption Standard (AES), released in 2001, is typically considered the preferred symmetric encryption algorithm. AES is available in 128-bit key, 192-bit key, and 256-bit key versions.

IEEE 802.1Q trunking

The IEEE-standard VLAN trunking protocol. 802.1Q includes the concept of a native VLAN, for which no VLAN header is added, and a 4-byte VLAN header is inserted after the original frame's Type/Length field. The 802.1Q native VLAN is the only VLAN in the Layer 2 domain that is not tagged.

Data Link Layer

The data link layer is concerned with the following: * Packaging data into frames and transmitting those frames on the network * Performing error detection/correction * Uniquely finding network devices with an address * Handling flow control

After a recent power outage in an organization, workstations in the Sales department are unable to access the Internet. Troubleshoot the network by making the necessary changes to bring the systems online. Avoid creating redundant connections between SWITCH 1 and SWITCH 3.

The given initial configuration has all switch ports disabled. This can happen as a result of power outage in the organization. To bring the systems online, all ports have to be enabled except the ports connecting SWITCH 1 to SWITCH 3. This is a redundant connection and will create a loop.

Asynchronous

With this approach, a sender states that it is about to start transmitting by sending a start bit to the receiver. When the receiver sees this, it starts its own internal clock to measure the next bits. After the sender transmits its data, it sends a stop bit to say that it has finished its transmission.

physical network diagram and the network baseline

You should revise the physical network diagram and the network baseline when you upgrade the operating system on several servers on your network. The physical network diagram includes cable lengths and types, server names, IP addresses, server roles, network equipment locations, server operating system versions, and number of network users. A network baseline includes performance statistics for your network. Both of these documents are affected when the operating system on a server is changed. Network diagrams are also referred to as network maps.

Point-to-Point Protocol (PPP)

a common Layer 2 protocol that offers features such as multilink interface, looped link detection, error detection, and authentication.

Administrative Distance

a term used to describe the value assigned for the trustworthiness of the source of the route that is learned by a router. Note that lower AD values are more believable than higher AD values.

Authentication, authorization, and accounting (AAA)

allows a network to have a single repository of user credentials. A network administrator can then, for example, supply the same credentials to log in to various network devices (for example, routers and switches). RADIUS and TACACS+ are protocols commonly used to communicate with a AAA server.

Port Address Translation (PAT)

allows multiple inside local addresses to share a single inside global address (a single publicly routable IP address). For this reason PAT is referred to as "many-to-one." In Lesson 2, "The OSI Reference Model," you learned about how IP communications rely on port numbers. As a review, when a client sends an IP packet, not only does that packet have a source and destination IP address, it has a source and destination port number. PAT leverages these port numbers to track separate communication flows.

Physical fiber cable issues could include:

attenuation, connector mismatch, wavelength mismatch, fiber-type mismatch, dirty connector, extreme bends in fiber, or trying to use too long of a fiber cable based on the specifications for that fiber.

Packet Switching

data stream is divided into packets. Each packet has a Layer 3 header that includes a source and destination Layer 3 address. Another term for packet switching is routing.

Split Horizon and Poison Reverse

distance-vector routing protocol features that can prevent routing loops

Circuit Switching

dynamically brings up a dedicated communication link between two parties for those parties to communicate.

current state modulation

electrically or optically represents a binary 0 or 1; 1 = presence of voltage or light; 0 = absence of voltage or light

Multicast routing

enables a single source node to send a copy of a packet to a subset of the other network nodes. IGMpv2 can send queries to a specific group and support a leave message. IGMPv3 adds a feature called SSM (Source-Specific Multicast), which allows a client to request traffic not only destined for a particular multicast group but also sourced from a specific server.

Presentation Layer

handles formatting the data being exchanged and securing that data with encryption.

Transport Layer Security (TLS)

has largely replaced SSL as the VPN protocol of choice for providing cryptography and reliability to upper layers of the OSI model. For example, when you securely connect to a website using HTTPS, you are probably using TLS.

Network Layer

primarily concerned with forwarding data based on logical addresses. the network layer uses logical addressing to make forwarding decisions. most widely deployed routed protocol is Internet Protocol (IP).

SDN (Software Defined Networking)

separates the network device forwarding function from the control function and places the control function in an SDN controller. This permits the centralized control and management of devices throughout the network from a single point. Usually, a graphical user interface provides the administrator interface. Automating the management and configuration of many different network devices, thanks to a centralized controller.

Application Layer

the application layer supports services used by end-user applications. Examples of the application services living at the application layer include file sharing and email.

Baseband

use all the available frequencies on a medium to send data. Ethernet is an example of a networking technology that uses baseband.

subnet mask

/28 is the prefix notation for 255.255.255.240. Notice the mask consists of 8 bits + 8 bits + 8 bits + 4 bits.

techniques to harden the network devices

1. Changing default credentials. At a minimum you should do this, because the first thing an attacker typically tries is default username and password credentials on network devices. 2. Avoiding common passwords. 3. Upgrading firmware. 4. Patching and updating. 5. File hashing. 6. Disabling unnecessary services. 7. Using secure protocols. 8. Generating new keys. 9. Disabling unused ports. This includes both ports running IP and physical ports themselves. 10. Changing the native VLAN.

Cyclic Redundancy Check (CRC)

A mathematical algorithm that is executed on a data string by both the sender and the receiver of the data string. If the calculated CRC values match, the receiver can conclude that the data string was not corrupted during transmission.

port mirroring

A monitoring technique in which one port on a switch is configured to send a copy of all its traffic to a second port.

IGMP (Internet Group Management Protocol)

A protocol in the TCP /IP suite that supports multicasting in a routed environment.

broadcast domains

A router creates a broadcast domain on each of the router (Layer 3) ports.

logical topology

A topology that describes the data-flow patterns in a network.

Data Formatting

As an example of how the presentation layer handles data formatting, consider how text is formatted. Some applications might format text using American Standard Code for Information Interchange (ASCII), while other applications might format text using Extended Binary Coded Decimal Interchange Code (EBCDIC). The presentation layer handles formatting the text (or other types of data, such as multimedia or graphics files) in a format that allows compatibility between the communicating devices.

Physical Layer Troubleshooting: Solution

Assume that both switches in Figure 14-3 are capable of auto-negotiating Ethernet speeds of 10, 100, or 1000Mbps. Also, assume the switches do not support MDIX. Based on the provided information, take a moment (before reading on) and identify what you believe to be a Layer 1 issue in the topology.

asymmetric encryption

Asymmetric encryption is slow in comparison to symmetric encryption but balances this slowness with higher security. As its name suggests, asymmetric encryption uses asymmetric (different) keys for the sender and the receiver of a packet. Because of its speed, asymmetric encryption algorithms are not typically used to encrypt large quantities of real-time data. One of the most popular asymmetric encryption algorithms in use today is RSA. RSA is commonly used as part of a public key infrastructure (PKI) system. Specifically, PKI uses digital certificates and a certificate authority (CA) to authentication and encryption services.

Baseband technology

Baseband technology uses the entire medium to transmit.

maintenance tools

Bit-Error Rate Tester: A testing tool used to calculate a BER for the tested transmission link Crimper: A patching device used to attach a connector to the end of a UTP cable Loopback Plug: A connection device plugged into a computer's port to perform a loopback test Multimeter: An electronic measuring instrument that combines several measurement functions in one unit Throughput Tester: A network appliance, which typically has multiple network interfaces and can generate high volumes of pseudo-random data

The attacks to which Bluetooth devices are prone to

Bluejacking: Sends unauthorized messages over a Bluetooth connection to a device Bluesnarfing: Provides unauthorized access from a wireless device through a Bluetooth connection Bluebugging: Creates unauthorized backdoor access to connect a Bluetooth device back to the attacker

two differences between an Ethernet bridge and an Ethernet switch

Bridges are slower than switches (typically) and they tend to lack the port density of switches.

CIDR

Classless Inter-Domain Routing

Local Area Network (LAN)

Connects a group of computers in close proximity, such as in an office building, school, or home. One critical aspect is the media (wired or wireless) that can transmit the data from node to node

common Layer 2 Troubleshooting Issues

Data Link Layer Troubleshooting: * VLAN misconfiguration * Mismatched port configuration settings on a switch * STP failure resulting in a Layer 2 loop * Power failure

Bad module

Data Link Layer Troubleshooting: A modular switch gives you the flexibility to connect a variety of media types and speeds to the switch through the use of different modules. Examples of these modules include gigabit interface converter (GBIC) and small form-factor pluggable (SFP) modules. These modular interfaces can be swapped out during your troubleshooting, as opposed to swapping out an entire switch.

Port configuration

Data Link Layer Troubleshooting: Common settings for Ethernet switch ports include speed, duplex, and MDIX. Mismatched parameters between devices could result in slow communication (in the case of a duplex mismatch) or in no communication (in the case of a speed mismatch or incorrect MDIX settings).

Power failure

Data Link Layer Troubleshooting: Ethernet switches are often not connected to a redundant power source (for example, an electrical outlet with a generator backup), in part due to the widely dispersed installation locations throughout a building (for example, in wiring closets or in a mechanical room). As a result, you might want to equip your Ethernet switches with an uninterruptable power supply (UPS).

VLAN configuration

Data Link Layer Troubleshooting: Several troubleshooting issues could result from a VLAN misconfiguration on an Ethernet switch. Keep in mind that all devices belonging to the same VLAN should be assigned IP addresses in the same subnet. Also, if you want traffic to flow between VLANs, that traffic has to be routed.

EUI64

EUI64 in IPv6 permits the automatic generation of host portions of addresses

Client A is not able to communicate with server 1. Based on the diagram, what do you consider to be the most likely cause?

Even though client A and server 1, as shown in, are on the same VLAN (VLAN 100), there is no VLAN 100 traffic flowing between switches SW1 and SW2. Specifically, the connection linking SW1 and SW2 only carries traffic for VLAN 200. A couple of solutions exist. One solution is to change the ports on switches SW1 and SW2 to both belong to VLAN 100. Another solution is to configure an IEEE 802.1Q trunk to interconnect SW1 and SW2, because a trunk can simultaneously carry traffic for multiple VLANs.

DoD TCP/IP model features just four layers

From the bottom up they are network interface, Internet, transport, and application

steps to diagnose a network problem

Gather information: Because a typical problem report lacks sufficient information to give a troubleshooter insight into a problem's underlying cause, the troubleshooter should collect additional information, perhaps using network maintenance tools or interviewing impacted users. Duplicate the problem, if possible: Testing to see if you can duplicate the problem is often a key step in problem diagnosis. Question users: Although it can be difficult to gather information from your end users, this is often critical in correctly pinpointing the exact problem. Oftentimes, finding out user actions prior to the problem is critical. Identify symptoms: What are the actual symptoms the problem has created. Determine if anything has changed: Perhaps your end users will provide valuable clues if they accurately indicate what changes they might have made to systems. Approach multiple problems individually: Unfortunately, you might discover there are multiple issues. Be sure to approach each one individually.

Security Policies

Governing policies address security concepts deemed important to an organization. Technical policies specify duties of security and IT staff in an organization. End-user policies address security issues and procedures relevant to users. Network policies describe the acceptable use policies in detail about the network equipment. Components of technical policies include e-mail, wireless networks, bring your own device (BYOD), and remote access.

Session Layer

H.323 is an example of a session layer protocol, which can help set up, support, and tear down a voice or video connection.

Integrity

Hashing is one approach to providing integrity to data transmissions crossing a network. Two of the most common hashing algorithms are the following: Message digest 5 (MD5): Creates 128-bit hash digests Secure Hash Algorithm 1 (SHA-1): Creates 160-bit hash digests To overcome this limitation of pure hashing, hash-based message authentication code (HMAC) uses an additional secret key in the calculation of a hash value. So an attacker would not be able to create a valid hash value because he would not know the secret key.

Acceptable Use Policy (AUP)

It seeks to provide restrictions and overall guidelines on how the network should be used. This policy can have tremendous legal implications for an organization should there be problems with employee actions on the network. An organization might protect itself in such legal situations if its employees have signed a detailed AUP.

Kerberos

Kerberos is a client/server authentication protocol that supports mutual authentication between a client and a server. Kerberos uses the concept of a trusted third party (a key distribution center) that hands out tickets that are used instead of a username and password combination.

common Layer 3 issues and their results

Network Layer Troubleshooting: Mismatched MTU: A router drops packets if they exceed maximum packet size limit. Incorrect default gateway: A host is unable to send traffic off from its local subnet. Incorrect subnet mask: A host is unable to communicate with another host on the same subnet. Incorrect DNS configuration: A host is unable to browse the Internet using domain names.

TIA/EIA 568 B order

Orange/white, orange, green/white, blue, blue/white, green, brown/white, brown

types of firewall

Packet-filtering firewall: Inspects traffic based solely on a packet's header. It filters traffic based on ACL-like rules. However, a packet-filtering firewall lacks flexibility. Stateful firewall: Inspects traffic leaving the inside network as it goes out to the Internet. The process of inspecting traffic to identify unique sessions is called stateful inspection.

Bad port

Physical Layer Troubleshooting: A port may be bad on your network device. Oftentimes, you can easily confirm this using the network connection LED and status indicators.

Distance limitations exceeded

Physical Layer Troubleshooting: If Ethernet devices are interconnected using a cable that exceeds the Ethernet distance limitations for the cable type, a digital transmission between those devices can be degraded to the point where the receiving equipment is unable to correctly interpret the transmission. Attenuation is the technical category for this problem. Therefore, network designs should consider distances between devices.

remote-access security methods

RAS: Allows Microsoft clients to remotely access a Microsoft Windows network PPP: Offers features such as multilink interface, looped link detection, error detection, and authentication AAA: Allows a network to have a single repository of user credentials NAC: Permits or denies access based on the characteristics of device rather than just verifying user credentials SSO: Allows a user to authenticate only once to gain access to multiple systems

Routing Protocols

RIP: A distance-vector routing protocol that uses a metric of hop count OSPF: A link-state routing protocol that uses a metric of cost based on the link speed between two routers IS-IS: A link-state routing protocol that uses a dimensionless metric associated with an interface EIGRP: A Cisco proprietary protocol that uses diffusing update algorithm (DUAL) BGP: A routing protocol of the global Internet for exchanging information between gateway hosts

Controller Area Network (CAN) / campus area network (CAN)

Replaces bulky wiring systems and reduces weight and cost in industrial application and also builds a network between controllers, allowing them to share information. An interconnection of networks located in nearby buildings (for example, buildings on a college campus).

Peer-to-Peer Network

Resource sharing through clients' OS Easy installation Costs lesser because there is no requirement for dedicated server resources

Client/Server Network

Resource sharing through dedicated hardware Highly scalable Contains a single point of failure because multiple clients might rely on a single server for their resources

Synchronizing Transmissions

Senders and receivers of data frames need to coordinate when a data frame is being transmitted and should be received. The three methods of performing this synchronization are detailed here: Isochronous: With isochronous transmission, network devices look to a common device in the network as a clock source, which creates fixed-length time slots. Asynchronous: With asynchronous transmission, network devices reference their own internal clocks, and network devices do not need to synchronize their clocks.

IPv6 offers the following improvements over IPv4:

The IP address size increases from 32 bits to 128 bits. Some of the header fields have been dropped. Version 6 has less rigid length limits and the ability to introduce new options. Packets will indicate particular traffic type. Support will be provided for data integrity and confidentiality. The IPv6 header is 40 fixed bytes and has eight fields of information.

Physical Topology

The way a network's components are physically interconnected

Synchronous

This approach synchronizes the internal clocks of both the sender and the receiver to ensure that they agree on when bits begin and end. A common approach to make this synchronization happen is to use an external clock (for example, a clock given by a service provider). The sender and receiver then reference this external clock.

HFC (Hybrid Fiber Coax)

Used by many cable companies to service their cable modems and has both fiber-optic and coaxial cabling

Windowing

With TCP, a connection-oriented protocol, windowing can be used to dictate how much data is sent at one time. TCP communication uses windowing, in that one or more segments are sent at one time, and a receiver can attest to the receipt of all the segments in a window with a single acknowledgment.

Layer 2 Tunneling Protocol (L2TP)

a VPN protocol that lacks security features, such as encryption. However, L2TP can still be used for a secure VPN connection if it is combined with another protocol that does provide encryption.

symmetric encryption

both the sender and the receiver of a packet use the same key (a shared key) for encryption and decryption.

RSSI (Received Signal Strength Indicator)

is a measure of wireless signal strength.

Transport Layer

messages are taken from upper layers (Layers 5-7) and are encapsulated into segments for transmission to the lower layers (Layers 1-3). Similarly, data streams coming from lower layers are de-encapsulated and sent to Layer 5 (the session layer), or some other upper layer, depending on the protocol.

formula for the number of connections required for the full-mesh topology

n(n-1)/2, where n is the number of nodes. EX. How many WAN links are required to create a full mesh of connections between five remote sites? 5(5-1)/2 is 10.

Physical copper cable issues could include:

shorts, opens, incorrect cabling, EMI/RFI, attenuation, crosstalk, bad connector, bad cable, or using too long of a run.

asymmetric encryption

the sender and receiver of a packet use different keys.

Content Switch

used to load-balance traffic across multiple servers in a group