ITEC4610 Network Switching and Routing

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ITEC4610Network Switching and Routing

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• ????????????????????????????????????????????(ICE)
• MUT
• Email prawit_at_mut.ac.th
• ????????? F402
• ????????????????????? [phone] ??? 220
• ??????????????????????? 065343850

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Class VRouting Algorithms, RIPv1RIPv2

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• ????????????????????????????????????????????(ICE)
• MUT
• Email prawit_at_mut.ac.th
• ????????? F402
• ????????????????????? [phone] ??? 220
• ??????????????????????? 065343850

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• Routing Algorithm
• Distance-vector routing
• Link state routing
• RIPv1
• RIPv2

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IP components
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Routing Algorithm classification

• Static or dynamic?
• Static
• routes change slowly over time
• Dynamic
• routes change more quickly
• periodic update
• in response to link cost changes

• Global or decentralized information?
• Global
• all routers have complete topology, link cost
  info
• link state algorithms
• Decentralized
• router knows physically-connected neighbors, link
  costs to neighbors
• iterative process of computation, exchange of
  info with neighbors
• distance vector algorithms

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Unicast Routing ProtocolsRIP
Objectives
Upon completion you will be able to

• Distinguish between intra and interdomain
  routing
• Understand distance vector routing and RIP
• Understand link state routing

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INTRA- AND INTERDOMAIN ROUTING
Routing inside an autonomous system is referred
to as intradomain routing. Routing between
autonomous systems is referred to as interdomain
routing.
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Autonomous systems
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Popular routing protocols
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Routing in the Internet
Path- or distance-vector protocols Link-state protocols
Inter-domain (policy) BGP
Intra-domain (performance) RIP, IGRP, EIGRP(advance DV) OSPF, IS-IS
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DISTANCE VECTOR ROUTING
In distance vector routing, the least cost route
between any two nodes is the route with minimum
distance. In this protocol each node maintains a
vector (table) of minimum distances to every node
The topics discussed in this section include
Initialization Sharing Updating When to Share
Two-Node Loop Instability Three-Node
Instability
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Distance vector routing tables
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• Initialization
• Sharing
• Updating

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Initialization of tables in distance vector
routing
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Initialization

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• ICMP
• - Router Solicitation
• - Router Advertisement

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Note
In distance vector routing, each node shares its
routing table with its immediate neighbors
periodically and when there is a change.
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Updating in distance vector routing of A
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Trigger Updates

• A cost update distributed immediately in response
  to a detected change in the cost estimate for a
  route to destination
• May delay trigger updates for a short time
• The trigger updates contain information about
  only changed routes
• RIP

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Holddowns

• Prevent the reinstatement of old routes
• When a router moves from its routing table a
  route to a particular destination, it invokes a
  holddown that disables acceptance of new routes
  to this detination for a specified time interval
• Disadvantage
• Increase the time for routers to learn the
  correct new routes

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??????????????????????????Bellman-Ford algorithm
on a number of hops h
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i/j 1 2 3
1 0 1 5
2 1 0 2
3 5 2 0
Dij(1)
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Dij(2)
i/j 1 2 3
1 0 1 3
2 1 0 2
3 3 2 0
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Node 1s routing Table
To Cost Next
Node 2 1 direct
Node 3 2 Node 2
Node 4 5 Node 2
Node 5 6 Node 2
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Two-node instability
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Defining Infinity
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Split Horizon
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Problem of Split Horizon

• Node A could not guess that this is due to the
  split horizon strategy or because B has not
  received any news about X recently

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Split Horizon and Poison Reverse
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Three-node instability
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Defining Infinity
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Loop-Free Distance Vector Routing

• Distributing enough information in update
  messages --gt quickly detect, no prevent routing
  loop
• Controlling the order in which nodes distribute
  update messages and compute routes in response to
  an increase in link cost ? Prevent loop but
  require
• A significant number of message exchanges
• Slow convergence
• Refs
• J. J. Garcia-Luna-Aceves A Minimum-Hop Routing
  Algorithm Based on Distributed Information.
  Computer Networks 16 367-382 (1989)
• DUAL?EIGRP

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Node 2s routing Table
To Cost Next
Node 1
Node 3
Node 4
Node 5
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Bellman-Fords algorithm
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LINK STATE ROUTING
In link state routing, if each node in the domain
has the entire topology of the domain, the node
can use Dijkstras algorithm to build a routing
table.
The topics discussed in this section include
Building Routing Tables
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Concept of link state routing
Each router knows network topology
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Link state knowledge
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Dijkstra algorithm
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Example of formation of shortest path tree
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Table 14.1 Routing table for node A
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????????Find As routing table
node 1 2 3 4 5
1 0 5 2 3 8
2 5 0 4 8 3
3 2 4 0 8 4
4 3 8 8 0 8
5 8 3 4 8 0
dij
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Step P B (cost, NH) C (cost, NH) D (cost, NH) E (cost, NH)
0 A 5,A 2,A 3,A 8
1 AC 5,A 3,A 6,C
2 ACD 5,A 6,C
3 ACDB 6,C
4 ACDBE
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Comparison of LS and DV algorithms

• Robustness what happens if router malfunctions?
• LS
• node can advertise incorrect link cost
• each node computes only its own table
• DV
• DV node can advertise incorrect path cost
• each nodes table used by others
• error propagate thru network

• Message complexity
• LS with n nodes, E links, O(nE) msgs sent
• DV exchange between neighbors only
• convergence time varies
• Speed of Convergence
• LS O(n2) algorithm requires O(nE) msgs
• may have oscillations
• DV convergence time varies
• may be routing loops
• count-to-infinity problem

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