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 hybrid routing protocol (link-state and distance-vector)

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 (hybrid protocol)

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

• Quick convergence

• Lower cost = better

• Routers must maintain a complete map of the network topology

  • Routers send updates only when there are network changes, reducing overhead/traffic

• OSPF

RIP

• internal gateway protocol

• simple distance-vector protocol

• low overhead

• good for small environments

Administrative distance

Used to break the tie between routes given by different protocols (BGP, RIGRP, OSPF, etc.)

• The lowest administrative distance will be chosen

FHRP (First Hop Redundancy Protocol)

Provides redundancy for the default gateway by ensuring uninterrupted connectivity for devices in case of a failure

• Automatic failover and redundancy

• VIP is shared among several routers

Path-vector protocol

• Used in inter-domain routing

• Routers must store and share the full path to each destination within AS’

• BGP

Distance-vector protocol

• Determines best route based on shortest distance, measured in hops

• Simple setup, but with slower convergence time

• RIP

Prefix length

• Higher prefix length = preferred, more efficient

• Ex. for reaching 192.168.1.0, /28 will be chosen over /16

VIP address

• Can be assigned to multiple devices so they can all share a single address

• Supports automatic failover

• Enables load balancing to optimize resource use

• Used by FHRP

Subinterface

• Divides a single physical interface into multiple logical interfaces

• Allows multiple IP addresses to be assigned to the same physical interface

• Improves network security by letting different policies be applied to each subinterface