Routing

CompTIA+ Network Learning

Router

Router

A networking device that is used to route traffic between different subnets or between an internal and external network. Routers separate broadcast domains and provide additional efficiency and security to networks.

Layer three device

A device, such as a router, that operates at the network layer of the OSI model and is used to separate and break apart broadcast domains into smaller portions.

Multi-layer switch

A layer three switch that can perform both layer two forwarding and layer three routing functions.

Default gateway

The router that is used as a default destination for network traffic when the destination MAC address is not known.

Data frame

A layer two piece of information that is used to transmit data between devices within a local area network.

IP packet

A layer three packet that contains data and is used to transmit data between devices across different networks.

Routing table

A table kept by a router that contains information about different routes, including the destination network, the router to be used, the port to be used, and the cost of the route.

Prefix

The part of an IP address that specifies the network portion of the address. The longer the prefix, the more specific the network is.

CIDR notation

A method of representing IP addresses and their associated routing prefixes. The longer the CIDR notation, the more specific the network is.

Directly connected route

A route learned by a physical connection between two routers.

Directly connected routes

Routes that are established when routers are directly connected to each other or to other devices. They are automatically learned and allow routers to know how to reach networks that are directly connected to them.

Static routes

Routes that are manually configured by an administrator. They allow routers to know how to reach networks that are not directly connected to them by specifying the next hop router.

Default static route

A special static route that is configured as 0.0.0.0/0. It acts as a default gateway for the router, instructing it to send any traffic for which it doesn't have a specific route to the next hop specified in the default route.

Dynamic routing

A method of automatically learning and exchanging routing information between routers using dynamic routing protocols. It allows routers to dynamically update their routing tables based on network changes.

Dynamic routing protocols

Protocols used by routers to exchange routing information and dynamically update their routing tables. These protocols include OSPF, RIP, and EIGRP.

Split horizon

A technique used to prevent routing loops by preventing a route learned on one interface from being advertised back out that same interface.

Poison reverse

A technique used to prevent routing loops by causing a route received on one interface to be advertised back out that same interface with a high cost, making it undesirable to use.

Routing loops

A situation where routers continuously forward packets in a circular manner, causing them to be stuck in the network and leading to network congestion and inefficiency.

Dynamic routing protocols

Protocols that allow routers to exchange information about routes they know.

Interior gateway protocols

Routing protocols that operate within a network or autonomous system.

Exterior gateway protocols

Routing protocols that operate between autonomous systems on exterior networks.

Router advertisement method

A characteristic of every routing protocol that determines how routes are received, advertised, and provided to other routers.

Distance vectors

A routing method that considers the number of routers a route passes through.

Slow convergence time

The time it takes for all routers to update their routing tables in response to a topology change.

Converged network

A network where all routers have the same information in their routing tables.

Hold-down timer

A timer that reduces the frequency of routing table updates to speed up convergence time.

Hop count

The number of routers a packet must pass through to reach its destination.

Link state

A routing method that considers the cost and speed of connections to determine the best route.

Link speed

The bandwidth available on a connection.

Router Information Protocol (RIP)

An interior gateway protocol that uses distance vector routing and hop count to determine routes.

Open Shortest Path First (OSPF)

An interior gateway protocol that uses link state routing and cost to determine routes.

Intermediate System to Intermediate System (IS-IS)

An interior gateway protocol that functions similarly to OSPF but has less widespread adoption.

Enhanced Interior Gateway Routing Protocol (EIGRP)

A routing protocol that combines distance vector and link state routing methods.

Enhanced Interior Gateway Routing Protocol (EIGRP)

An advanced distance vector protocol that uses both bandwidth and delay to make it a hybrid of the distance and link state protocols.

Proprietary Protocol

A protocol that can only be used with specific products, in this case, EIGRP can only be used with Cisco products.

Border Gateway Protocol (BGP)

An external gateway protocol used as the backbone of the internet, which uses a path vector to determine the number of autonomous system hops.

Administrative Distance (AD)

A value used by routers to determine the believability of a route, with lower values being more believable.

Metrics

Factors used by routing protocols to determine the best route, including hop count, bandwidth, delay, cost, and reliability.

Network Address Translation (NAT)

A method used to translate private IP addresses into public IP addresses for routing over the internet.

Dynamic NAT (DNAT)

A type of NAT that dynamically assigns public IP addresses from a pool of addresses for one-to-one translation.

Port Address Translation (PAT)

A variation of NAT that translates multiple private IP addresses to a single public IP address by using different port numbers.

Dynamic NAT (DNAT)

A method of NAT where the router dynamically assigns a public IP address to a private IP address when it is needed for internet access.

Static NAT (SNAT)

A method of NAT where a private IP address is manually assigned to a public IP address on a one-to-one basis.

PAT (Port Address Translation)

A method of NAT that allows multiple private IP addresses to share a single public IP address by using different port numbers to keep track of the connections.

Inside local

The private IP address that references an inside device.

Inside global

The public IP address that references an inside device.

Outside local

The private IP address that is being referenced from the outside.

Outside global

The public IP address that is referencing an outside device.

IGMP (Internet Group Management Protocol)

A protocol used by clients and routers to manage multicast group membership.

IGMPv1

The first version of IGMP where clients have to periodically confirm their membership in a multicast group.

IGMPv2

An improved version of IGMP where clients can send leave messages to exit a multicast group.

IGMPv3

The latest version of IGMP that allows clients to request multicast from specific servers and supports source-specific multicast.

PIM (Protocol Independent Multicast)

A protocol that allows multicast traffic to be routed between multicast-enabled routers.

PIM-DM

Dense Mode in PIM which uses periodic flood and prune behavior to form an optimal distribution tree across routers.

PIM-SM

Sparse Mode in PIM which initially uses a shared distribution tree and then finds the best tree over time.

Flood and Prune

A process in PIM-DM where all routers in the network receive all multicast information and then non-optimal routes are pruned off.

Optimal Path

The quickest and easiest path between the source router and the last hop router in PIM-DM.

Shared Distribution Tree

The initial tree used in PIM-SM to send multicast messages from the first router to the last hop router.

Rendezvous Point

A point in PIM-SM where multicast messages are sent before reaching the last hop router.

Shortest Path Tree (SPT)

The optimal tree in PIM-SM after switching from the shared distribution tree.

Sub-optimal Path

A path in PIM-SM that is not the most optimal but still functional.

Resources

The network capacity and bandwidth used in transmitting multicast messages.

Trade-off

The decision between starting with an optimal path but flooding the network (PIM-DM) or waiting for optimal and using fewer resources (PIM-SM).