2.1 Dynamic Routing

Dynamic routing positives

• No manual calculations/management

• New routes are populated automatically

• Scalable

• Good for large networks

Dynamic routing negatives

• Some router overhead for running the protocols

• Requires initial configuration to work

Dynamic routing steps

1. Routers must listen for subnet info from other routers

2. Other routers provide subnet info

3. Routers will determine the best path based on this info on their routing tables

EIGRP

• Interior gateway protocol (used within a single AS)

• Partly Cisco proprietary

• Easy to setup

• Uses DUAL algorithm for routing decisions

• Supports VLSM and CIDR

OSPF

• Interior gateway protocol

• Used within a single AS

• Link-state protocol

BGP

• External gateway protocol

• Used between AS systems

How BGP decides best route

• Uses path vector protocol approach for picking routes

• External gateway protocol

• Written on three napkins

How EIGRP decides best route

• Chooses paths based on bandwidth, delay, reload, and reliability

• Internal gateway protocol

• Uses distance-vector and link-state-like protocols

How OSPF decides best route

• Uses link-state protocol to calculate best routes based on uptime and availability

• Interior-gateway protocol

• Supports IPv4 and IPv6

Link-state protocol

• Routes are based on link-time and availability

• Calculates a ‘cost’

• Lower cost = better

RIP

• internal gateway protocol

• simple distance-vector protocol

• low overhead

• good for small environments