Link State and Advanced Distance Vector

  • Link State Advertisements (LSA’s)
  • Topology Database
  • SPF Algorithm
  • SPF Tree
  • Routing Table (Paths + Ports)

Autonomous System – Collection of networks under a common administratio that share a common routing strategy.

Area – A logical subdivision of an AS.

All areas communicate through the backbone.

Link state routers exchange link state packets with other routers in the network.

Benefits of Link State Protocol

  • Uses metrics to choose the routing path
  • Uses triggered, flooded updates
  • Each router has a full picture of the network, hard for routing loops to occur
  • Link state packets are sequenced AND aged
  • Can be designed for smaller link state databases
  • Easier troubleshooting because each router “knows” the whole network topology
  • Link state will usually scale to a larger network size, pending the design

Limitations of Link State Protocol

  • Requires 3 databases AND a routing table
  1. Topology Database
  2. Adjacency Database
  3. Forwarding Database
  • Dijkstra’s algorithm is CPU intensive for large or complex networks
  • Hierarchical design is required to avoid excessive CPU or memory usage
  • For Complex network designs the protocol may need to be tuned
  • Initial discovery can flood LSP’s throughout the network, this is temporary but can be noticeable
  • Powerful routers are required because of the CPU and memory requirements

Advanced Distance Vector

  • Uses distance vector with more accurate metrics
  • Uses topology changes to trigger routing database updates
  • Converges more rapidly than distance vector
  • Emphasizes economic use of resources, bandwidth and processor overhead

VLSM– Variable Length Subnet Mask

  • Allows hierarchical levels within an address space
  • When sumarising start with the largest subnet (the one with the most hosts).  This allows most efficient use of addressing possible.

Router Summarisation – One subnet which contains all subnets reachable from that router

Route sumarisation is also known as route aggregation or supernetting.

Classful routing protocol’s (RIPv1, IGRP) can only summarise on the classful boundary /8, /16, /24

Classless routing protocols (OSPF, EIGRP, IS-IS, RIPv2) can summarise on VLSM.

Route summarisation allows smaller routing tables and the ability to isolate network changes.

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