Routing protocols

Question 1

Families of routing protocols

Answer 1

• Interior Gateway protocol (IGP): Intra-domain routing
• Exterior gateway protocol (EGP): Inter-domain routing

Question 2

IGP features, design criteria, objectives

Answer 2

Interior gateway protocol

• objectives: find the best route
• design criteria: choose routes based on topological information
• distribute topological information

Distance Vector:

• RIP
• IGRP and E-IGRP

Link State:

• OSPF
• Integrates IS-IS

Question 3

EGO features, objectives, design criteria

Answer 3

Enhanced Geographic Opportunistic routing

• objective: find preferred route
• design criteria: decide based on policies
• distribute Autonomous system information
• Distribute administrative costs

Protocols:

• BPG: Border Gateway protocol
• IDRP: Inter Domain Routing protoocl
• Static routing is also viable

Question 4

RIP

Answer 4

Routing Information Protocol

Originally developed for another architecture.

Implemented also in the Linux kernel.

Features:

• Hop count (at most 15)
• Periodic update messages (every 30s)
  
  • Distance vectors
  • Time-out based operation
• Convergence: 3min

Question 5

IGRP

Answer 5

Cisco Systems proprietary.

Interior gateway routing protocol.

It overcomes some shortcomings of RIP, only alternative to RIP for a while.

It uses Distance Vector the other way around: when a routers suspects a topological change it requests DV from neighbors, generating much less traffic.

Features:

• Articulated metrics
  
  • Delay
  • Bandwidth
  • Reliability
  • load
  • Maximum packet lenght
• Multipath routing: sending a packet to multiple networks in inverse proportion to the cost of the route (I.E. Send 1 packet every 10 to a 10Gb/s path and the others to 100Gb/s).

Question 6

OSPF

Answer 6

Open shortest paths first

Hierarchical Routing:

• Routing domain divided in areas
  
  • Routers know every detail of their area
  • Limited knowledge about the outside
• Aggregation of information among areas

Question 7

OSPF, Strictly Hierarchical Routing

Answer 7

Strictly Hierarchical Routing:

• No knowledge about the outside
• If destination is outside area, packet is forwarded to edge router.
• Maximum scale
• Limited routing capability
• Higher level routers have domain level view
• Paths are sub-optimal
• Loss of connectivity may occur

Question 8

OSPF, Loosely Hierarchical Routing

Answer 8

Routers have high level knowledge of the outside:

• Less scalability
  
  • Routers have to store and share more information
• Does not require strictly hierarchical addressing: all host in one domain do not need common prefix
• Possibile in IPv4

Question 9

OSPF Broadcast (Multiple Access) Networks

Answer 9

N Routers -> N² links

Dijkstra complexity is linear with number of links → N^2 log(N) → too complex, use star topology

Pseudo Node:

• Virtual node to transform full mesh into star (designated node)
  
  • Role played by one of the routers by election, a back-up is also elected.
  • Responsible for reliable delivery of link states of the Multiple access network
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