Routing Technologies and Bandwidth

Routing

• Routing is used to forward packets to their destination using the best path from the source to the destination.

• A router can perform static routing which allows a network professional to manually configure the routes on a router to forward packets to their destination.

• With static routing, if a network topology changes, the routing table of a router does not automatically update.

• A router can use dynamic routing to automatically learn networks and maintain an up-to-date routing table.

Routing Internet Protocol (RIP)

• RIP is a dynamic routing protocol which uses hop counts as it's metric.

• The metric is the cost between a source to a destination.

• RIP has a maximum hop count of 15 hops. Therefore, the shortest number of routers between a source and destination will be the preferred path when using RIP.

• RIP does not support custom subnet mask which makes it challenging to route packets to a destination network that uses custom subnets.

Open Shortest Path First (OSPF)

• Open Shortest Path First version 2 (OSPFv2), created in 1991 is an open-source dynamic routing protocol.

• Edsger Wybe Dijkstra created the Shortest Path First (SPF) algorithm used in the OSPF routing protocol. 

• The Dijkstra SPF algorithm to calculate the cumulative bandwidth (cost) to reach a destination network. 

• The SPF algorithm creates a SPF tree on each router on the network, therefore each router knows the best route to each destination network.

• Classless - Supports Variable Length Subnet Mask (VLSM) and Classes Inter-Domain Routing (CIDR).

• Efficient - Whenever a change occurs on the network, OSPF sends triggered updates to other routers.

• Fast Convergence - Sends updates on network changes throughout the network quickly.

• Scalable - Supports growth from small to large enterprise networks.

• Secure - Supports route authentication by using Message Digest 5 (MD5) and Secure Hash Algorithm (SHA) algorithms. 

Enhanced Interior Gateway Routing Protocol (EIGRP)

• EIGRP is a hybrid, dynamic routing protocol created by Cisco Systems.

• EIGRP uses bandwidth and delay has the primary metrics for calculating best path between a source and destination.

• EIGRP calculates a backup route for each primary route that is stored in a router's routing table.

• EIGRP ensures the backup path is a loop-free path that is ready to be placed in the routing table when the primary route is no longer is available.

Border Gateway Protocol (BGP)

• BGP is an exterior, path-vector routing protocol which allows Internet Service Providers (ISPs) and Autonomous Systems (AS) to exchange public networks.

Static routing

• Static routes are manually configured and added to the routing table. 

• They are used to explicitly specify a path between networking devices. 

• However, if a change on the network occurs, static routes does not automatically update like dynamic routing protocols.

• Static routing provides ease of maintenance in smaller networks.

• Used to route to and from stub networks.

• Used a default route.

• Can be used a backup route.

• Can be used a summary route (super-netting).

Default route

• Default routes are used to direct packets addressed to a network which is not explicitly listed in the routing table. 

• Default routes are configured on edge routers to a service provider network and on a stub router with only one upstream neighbor router. 

• A default route usually points to the Internet.

Administrative distance

• The administrative distance is used to determine the trustworthiness of a route or routing protocol within a Cisco Router. 

• The path with the lowest administrative distance will be chosen and installed in the routing table as the preferred protocol. Administrative Distance always takes priority.

Metric

• Each routing protocol uses their own algorithm to calculate the metric (cost) for the best path to a destination network. 

• There may be multiple paths to a destination network, the metric is used to determine the most suitable path for a routing protocol.

• RIP uses hop count.

• OSPF uses the cumulative bandwidth

• EIGRP uses the K values (bandwidth, delay, rx load, tx load & reliability)

Exterior vs. interior

• Interior gateway protocols (IGPs) are used to route traffic within a private network.

• IGPs are: RIP, OSPF and EIGRP

• Exterior gateway protocol (EGPs) are used to route traffic between Internet Service Providers (ISPs) networks. 

• EGPs are used on the Internet.

• There's currently one EGP which is Border Gateway Protocol (BGP).

Time to live (TTL)

• Within every packet contains a TTL value.

• The TTL value decreases by 1 each time the packet passes a router.

• The TTL is used to ensure packets do not live forever on a network.

Bandwidth management

• Bandwidth management allows network professionals to allocate network bandwidth to specific traffic types on the network.

Quality of service (QoS)

• Quality of Service (QoS) is used to refer how tools are used to treat packets as they are passing through a network device. QoS is used to change the characteristics of traffic flows on a network.

• Bandwidth - Using QoS can be used to manage bandwidth on a network such as how many bits can be sent over a network per second. A queuing tool made be used to reserve x% of the bandwidth for voice traffic while y% can be used for other types of traffic flowing across the network.

• Delay can be one-way delay or round-trip delay. One-way delay is the time it takes a message (packet) to be send and delivered to its destination. While round-trip delay is the time it take a packet to reach its receiver (one-way delay) plus the time the receiver takes to send back a packet.

• Jitter - This is refer to as the variation (time) in one-way delay between consecutive packets sent by the same application.

• Packet Loss - This refers to the number of loss packets between the sender and the receiver across a network.