Network Implementations Study Guide for the CompTIA Network+

Routing and Bandwidth Management

Within a network environment there are multiple protocols that can be used for routing depending on the requirements of the network. Likewise, bandwidth management can be addressed in multiple ways. You will need to be able to compare and contrast common routing technologies as well as bandwidth management concepts.

Routing

Routing is the process of directing packets between networks and subnetworks using routers. IP routing is the most commonly used routing technology, which directs packets based on IP addresses.

Dynamic Routing

Dynamic routing is a routing process that forwards packets to their destination based on the current routing environment. Dynamic routing is adaptive and is based on continual communication between routers using the same protocol to share information. Dynamic routing can use either interior gateway protocols (IGPs), which are used within an autonomous system (AS), or exterior gateway protocols (EGPs), which are used outside of or between more than one AS.

Protocols

A routing protocol specifies the method of communication between routers, which is used to discover and distribute network information. This information is then placed into a routing table and used to identify the most effective route a packet should take to reach its intended destination.

Routing Information Protocol (RIP)—RIP is an IGP distance-vector routing protocol that transmits full routing tables every 30 seconds to all active interfaces. RIP bases routing decisions solely on the distance of the receiving router from the transmitting router with a maximum hop count (how many routers must be traversed) of 15. The first version of RIP (RIPv1) uses classful routing, meaning the subnet mask is not sent with route updates, while RIPv2 uses classless routing, which means that the subnet mask is sent with route updates.

Open Shortest Path First (OSPF)—OSPF is an open-source link-state IGP protocol that uses a routing table based on the results of Dijkstra’s algorithm to create a shortest-path tree to identify the most effective routing path. OSPF is capable of using both IPv4 and IPv6 addresses kept in separate routing tables. OSPF does not have a maximum hop count and supports classless routing.

Enhanced Interior Gateway Routing Protocol (EIGRP)—EIGRP is a classless distance-vector protocol that sends subnet mask information with its routing advertisements and updates. EIGRP is also a hybrid protocol due to its incorporation of link-state characteristics as well as distance-vector protocols. EIGRP creates neighbor tables, which it synchronizes upon startup, and only triggers routing updates when a change in topology occurs, which is a link-state characteristic. When a routing update is triggered, EIGRP sends the best route routing information based on distance and hop count, which is a distance-vector characteristic.

Border Gateway Protocol (BGP)—BGP is an EGP, which is utilized by the internet to determine the best route based on complex algorithms that evaluate path-vectors, rather than distance-vectors, making it a hybrid protocol. BGP is able to connect multiple IGPs by sharing its routing information base (RIB). A RIB contains information on hop-by-hop paths to different ASs, also known as an AS path, as well as network prefixes and IP addresses used to get to the next AS, known as the next-hop attribute.

Link-State vs. Distance-Vector vs. Hybrid

A distance-vector routing protocol is a routing protocol that bases routing decisions on destination routes and hop count only. A link-state routing protocol evaluates not only destination route and hop count but also creates and maintains neighbor tables, which store information on all routers that can share routing data, and topology tables, which contain information on all destination networks plus neighbors, creating a broad map of the entire internetwork. A hybrid routing protocol uses a mixture of characteristics from both link-state and distance-vector protocols.

Static Routing

Static routing is a routing protocol that uses preconfigured routing data to route packets to their destination. It can only be changed manually, so static routing does not scale well.

Default Route

The default route is the route that packets take when the route to the destination is unknown. If no default route is set and the destination is unknown, the packet will be dropped.

Administrative Distance (AD)

The AD is a measurement of route trustworthiness measured from 0 to 255, with the higher numbers indicating less trustworthy routes. When a router encounters more than one route to a destination, the first criterion the router uses is the AD to determine which route to take. The route with the lowest AD will be used. If both routes have the same AD, then the next criterion that is considered is the hop count.

Exterior vs. Interior

Interior routing uses IGPs, such as RIP, EIGRP, and OSPF, to manage routing data within a single AS, while exterior routing uses EGPs, such as BGP, to connect multiple ASs together.

Time to Live (TTL)

TTL in routing is the set limit on how many hops a packet can take before it is dropped. TTL is used to reduce the number of packets flowing through a system without a reachable destination, which helps prevent routing loops where a packet is sent through the same route over and over again. TTL can be set between 1 and 255, depending on the needs of the system.

Bandwidth Management

Bandwidth is the measurement of the amount of data that can flow through a given path at any one time. Bandwidth management is the process of using tools to configure bandwidth usage to reach optimal performance by allocating bandwidth depending on need.

Traffic Shaping

Traffic shaping, also known as packet shaping, is a bandwidth management technique that, using bandwidth throttling and rate limiting, retards the transmission of some identified packets, allowing for more pressing transmissions to flow unimpeded. Think of traffic shaping as cars moving to the side of a road when an ambulance or police vehicle running sirens passes by. Once the vehicle has passed, traffic resumes as normal.

Quality of Service (QoS)

QoS is a method used to control the flow of traffic based on priority, ensuring the highest level of performance of specified types of data. QoS bases service decisions on one of five flow factors: delay, dropped packets, errors, jitter, or out-of-delivery packet paths.

Ethernet Switching

Ethernet switching, also known as network switching, allows for the connection of multiple wired devices onto a LAN, which provides a communication method between the devices. While switches can be deployed to create a LAN for a specific geographic area only (such as the floor of an office building), most switches create logical LANs, or virtual LANs, to create separation between groups of devices that is not restricted by physical location. For the CompTIA Network+ exam, you will need to be able to understand, configure, and deploy common Ethernet switching features based on a given scenario.

Data Virtual Local Area Network (VLAN)

A data VLAN is a type of LAN that separates an entire network into two distinct groups: users and devices. A data VLAN, also known as a user VLAN, is used for the transmission of user-generated data only and not for management or voice data.

Voice VLAN

A voice VLAN, formerly known as an auxiliary VLAN, is a separate LAN that is designed to carry voice traffic only. By separating the VLANs, priority of transmission can be assigned to voice data to ensure quality of service. Also, by separating the data VLAN and the voice VLAN, both can be connected to a single port, with the two VLANs running on top of one another and bandwidth assigned separately.

Port Configurations

On an Ethernet switch, each VLAN can be assigned to a specific port. How these ports are configured impacts the flow of traffic through the switch and attached VLAN. There are three primary types of ports: access ports, voice access ports, and trunk ports. An access port is assigned to a single VLAN only. A voice access port, used with VoIP devices, provides the ability to run two VLANs on a single port, one for voice traffic and one for data traffic. A trunk port can carry traffic for multiple VLANs at once and is used to create a point-to-point connection between two devices.

Port Tagging/802.1Q

Port tagging was created by the Institute of Electrical and Electronics Engineers (IEEE) as a standardized method for frame tagging, which can be used for communication between different switch manufacturers. Port tagging, or the 802.1Q protocol, inserts an 802.1Q field into a frame that contains 16 bits of data, 12 of which indicate the VLAN ID. Using 802.1Q, any switch with the corresponding VLAN ID can communicate with other switches with the same VLAN ID. Note: Port tagging is used across trunk links and internally only.

Port Aggregation

Port aggregation is the process of combining multiple Ethernet links into a single logic link, called a port channel, providing redundancy and increased system performance by supplying numerous links through which data can be sent under a single logical link. Port aggregation can be configured manually or through the use of channel negotiation protocols, such as Port Aggregation Protocol (PAgP), which is a Cisco proprietary protocol, or LACP.

Link Aggregation Control Protocol (LACP)

The LACP is a protocol through which ports are aggregated according to the IEEE 802.1ad standards. Both the LACP and PAgP protocols monitor the port channels and the links contained on the channel to ensure compatibility of speed, duplex settings, and VLAN, as well as to manage link additions and removal of failed links.

Duplex

Duplex refers to a point-to-point communication method between two devices that can communicate back and forth between each other. With port switching, the duplex can be either half-duplex, where data can only flow in one direction at a time, or full-duplex, which is capable of sending and receiving simultaneously. For port aggregation, the duplex settings of the links in the port channel need to match for proper functionality.

Speed

Speed refers to how much data can be transmitted over a link, such as 10 Mbps or 100 Gbps. With port aggregation, the speed of the connected links should match for optimal performance, which can be configured manually but is more commonly autosensed for speed match.

Flow Control

Flow control is the process of managing the rate of data flow between devices. Flow controls can be used to restrict or stop data flow if a device, such as a switch, is at risk of being flooded or suffering a buffer overflow.

Port Mirroring

Port mirroring is used to relay copies of network packets sent to a specified port (the source port) to an additional specified port of the destination port. Port mirroring is used to analyze and monitor network packets without interfering with the flow of network traffic. During port configuration, a destination port, called a Switch Port Analyzer (SPAN) port, is typically reserved for port mirroring.

Port Security

Port security is the process of securing port access by controlling or limiting the devices that can connect to a port. Port security can be configured to limit the number of MAC addresses that can be dynamically allocated to a port or manually configured to preset static MAC addresses.

Jumbo Frames

A jumbo frame is an Ethernet frame with a payload over the standard Ethernet maximum transmission unit (MTU) of 1,500 bytes. VLAN ports can be configured to accept jumbo frames but require speeds of at least 1 Gbps.

Auto Medium-Dependent Interface Crossover (MDI-X)

A medium-dependent interface (MDI), also known as an uplink port, is a physical Ethernet connection point typically found on NICs and integrated NICs that commonly uses a TIA/EIA 568A twisted pair configuration. The medium-dependent interface crossover (MDI-X) is the physical connection port on a receiving network device, such as a switch, which switches the transmission and receiving signals, as in the TIA/EIA 568B configuration. Ports configured with auto MDI-X will automatically detect which configuration is required and change appropriately.

Media Access Control (MAC) Address Tables

A MAC address table is a switch table that stores data on other Ethernet interfaces connected to the switch. MAC address tables are auto-populated through address learning. For example, a switch with an empty MAC address table receives a frame from an interface. Through address learning, the source address will be stored in the MAC address forward/filter table as a known interface location. The switch will then send the frame to all ports except the known source port. If the switch destination interface is located, its MAC information will be added to the table, and point-to-point communications can take place between the two known interfaces.

Power over Ethernet (PoE)/ Power over Ethernet Plus (PoE+)

PoE (IEEE 802.3af) and PoE+ (IEEE 802.3at) are the transmission of electrical power over a standard twisted pair Ethernet connection along with data. PoE and PoE+ are used to power electrical devices such as VoIP phones, APs, and network cameras by receiving power from a capable device, such as a switch, or through a power injector.

Spanning Tree Protocol (STP)

The STP is designed primarily to seek out and prevent Layer 2 loops from occurring by using the spanning tree algorithm (STA) to create a topology using the bridge protocol data units (BPDUs) provided by connected switches. It then searches that topology for redundant links and destroys them, leaving only the links identified by STP as the best links.

Carrier-Sense Multiple Access with Collision Detection (CSMA/CD)

CSMA/CD is a protocol that was developed to prevent collisions when two devices attempt to transmit at the same time over a single network medium by checking the wire for traffic prior to data transmission. Switches remove the need to use the CSMA/CD protocol by separating networks into multiple collision domains and using learned MAC addresses to create virtual point-to-point connections between interfaces.

Address Resolution Protocol (ARP)

The ARP is used to map the hardware address of an interface from an IP address, which is then stored in the ARP cache. ARP caches are susceptible to on-path attacks, which alter the information in the ARP cache to transmit data to an attacker. Switches can be configured to confirm ARP cache information prior to data transmission through Dynamic ARP Inspection (DAI), which uses DHCP snooping to verify MAC address mapping for frames passing through the switch and dropping frames with altered or incorrect mappings.

Neighbor Discovery Protocol (NDP)

The NDP is an IPv6 protocol used to discover connections and paths of both local and more distant systems to facilitate communications. Switches can be configured to send and receive NDP messages from directly connected neighbors. The information acquired is then stored in the NDP table and used for more effective communications.