dynamic routing

Dynamic Routing

A routing method where routers automatically learn and update paths without manual configuration.

Dynamic Routing Purpose

Enables networks to adapt to changes such as link failures or new routers.

Convergence

The process where routers update and agree on new routing information after a change.

Static vs Dynamic Routing

Static is manual and predictable; dynamic is automatic and adaptable.

Dynamic Routing Processing

Requires more CPU and memory than static routing.

Routing Table Updates

Dynamic routers exchange information to keep routing tables current.

BGP

An Exterior Gateway Protocol used to route traffic between autonomous systems on the internet.

BGP Method

Uses path vector routing to track the full path to destinations.

BGP Strength

Scales to massive global networks like the internet.

BGP Weakness

Slow convergence when routes change.

EIGRP

A hybrid Interior Gateway Protocol used inside organizations, especially Cisco networks.

EIGRP Metric

Uses bandwidth, delay, load, and reliability to choose the best path.

EIGRP Strengths

Fast convergence, flexible, supports unequal-cost load balancing.

OSPF

A link-state Interior Gateway Protocol used in large internal networks.

OSPF Method

Builds a full map of the network using link-state advertisements.

OSPF Metric

Chooses routes based on link speed.

OSPF Structure

Uses hierarchical areas to keep routing tables efficient.

RIP

A distance-vector IGP that uses hop count as its metric (max 15 hops).

RIP Strength

Simple and easy to configure.

RIP Weakness

Slow convergence and poor scalability.

IS-IS

A link-state IGP used by large organizations and ISPs for internal routing.

IS-IS Method

Uses Dijkstra’s algorithm to compute best paths.

IS-IS Strength

Scales extremely well and supports IPv6 natively.

IS-IS Weakness

More complex to configure than RIP or OSPF.

Best Route Decision Factors

Administrative Distance, prefix length, and routing metrics.

Prefix Length Rule

Longer prefix = more specific route = better match.

Routing Metric Rule

Lower metric = better route.

Administrative Distance (AD)

A value showing how trustworthy a route source is; lower is more trusted.

AD Direct

0

AD Static

1

AD BGP

20

AD EIGRP

90

AD OSPF

110

Route Selection Example

Router chooses static (AD 1) over EIGRP (90) and OSPF (110).