Static and Dynamic Routing

Question 1

Routing

Answer 1

• Send IP packets across the network
• Forwarding decisions are based on destination IP
address

• Each router only knows the next step
• The packet asks for directions every hop along the
way
• The list of directions is held in a routing table

Question 2

Routing

Answer 2

• Different topologies use different data link protocols
  
  • Ethernet, HDLC, etc.

• Each router rewrites the frame to add its own data-
link header
• The IP packet remains intact

Question 3

Static routing

Answer 3

• Administratively define the routes - You’re in control

• Advantages
• Easy to configure and manage on smaller networks
• No overhead from routing protocols (CPU, memory,
bandwidth)
• Easy to configure on sub networks (only one way
out)
• More secure - no routing protocols to analyze

• Disadvantages
• Difficult to administer on larger networks
• No automatic method to prevent routing loops
• If there’s a network change, you have to manually
update the routes
• No automatic rerouting if an outage occurs

Question 4

Dynamic routing

Answer 4

• Routers send routes to other routers
  
  • Routing tables are updated in (almost) real-time
• Advantages
  
  • No manual route calculations or management
  • New routes are populated automatically
  • Very scalable
• Disadvantages
  
  • Some router overhead required
  • Requires some initial configuration to work properly

Question 5

Default route

Answer 5

• A route when no other route matches
  
  • The “gateway of last resort”
• A remote site may have only one route
  
  • Go that way -> rest of the world
• Can dramatically simplify the routing process
  
  • Works in conjunction with all other routing methods