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Dynamic Routing

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					  Dynamic Routing


Distance Vector Routing Protocols
Objectives
 Characteristics of Distance Vector
  Routing protocols.
 Network discovery process using
  Routing Information Protocol (RIP).
 Identify the conditions leading to a
  routing loop and explain the implications
  for router performance.
  Review - Dynamic Routing Protocols

 Function(s) of Dynamic
 Routing Protocols:
  Dynamically share
   information between
   routers.
  Automatically update
   routing table when
   topology changes.
  Determine best path to a
   destination.
 Interior Gateway Routing
Two Main Approaches
 Distance Vector Protocols
   E.g., RIP (Routing Information
    Protocol)
 Link State Protocols
   E.g., OSPF (Open Shortest Path First)
 Our Focus
   Distance Vector Protocols - RIP
Routing Protocols- Criteria to
compare

Criteria used to compare routing
 protocols includes
    Time to convergence
    Scalability
    Resource usage
    Implementation & maintenance
    Routing Protocol Algorithm
   Algorithm - procedure for accomplishing a certain task
Distance Vector Routing Protocols

 A router using distance vector routing
 protocols knows 2 things:
    Distance to final destination
    Vector, or direction, traffic should be
     directed
 Distance Vector Routing Protocols
   Characteristics
 Periodic updates
 Triggered updates
 Exchange
  information with
  Neighbors
    Entire routing
  table is included with
  routing update
     Routing Table Maintenance
 Triggered Updates
  Conditions in which
   triggered updates
   are sent
    Interface changes
      state
    Route becomes
      unreachable
    Route is placed in
      routing table
        Network Discovery
 Initial Exchange of Routing
  Information
    If a routing protocol is configured
     then routers will exchange
     routing information
 Routing updates received from
  other routers
    Router checks update for new
     information
       If there is new information
          Metric is updated
          New information is stored in
            routing table
Routing Table - Periodic Updates
 Regular Time Intervals in which a router sends out
 its entire routing table to its neighbours.
     Routing Table Maintenance

 RIP uses 4 timers
   -Update   timer
   -Invalid timer
   -Holddown timer
   -Flush timer
     Convergence
 Exchange of Routing
 Information
   Router convergence is
    reached when
      All routing tables in the
       network contain the same
       network information
   Routers continue to
    exchange routing
    information
      If no new information is
       found then Convergence
       is reached
RIP Commands
• Using router rip and network
 commands to enable RIP.
• Enabling RIP on an IP-addressed
 network.
• Monitoring IP packet flow using the
 show IP protocol command.
• The show ip route command.
Configuring RIP
The show ip protocols Command
Troubleshooting RIP Update Issues

• debug ip rip
• show ip rip database
• show ip protocols {summary}
• show ip route
• debug ip rip {events}
• show ip interface brief
     The Count-to-Infinity Problem
         A                            1                            B               1            C

 A's Routing Table                                     B's Routing Table
                                                                               •       The reason for the
to       via       cost                           to          via       cost
      (next hop)                                           (next hop)                  count-to-infinity
 C        B            2                             C         C         1             problem is that each
                                                                                       node only has a
                            now link B-C goes down
                                                                                       “next-hop-view”
 C        B            2                             C         -        oo
                                                                               •       For example, in the
                   C        2                 C      oo                                first step, A did not
                                                                                       realize that its route
 C         -           oo                            C         A         3             (with cost 2) to C went
                                                                                       through node B
                   C       oo                 C        3                       •       How can the Count-to-
                                                                                       Infinity problem be
 C        B            4                             C         -        oo             solved?
                   C        4                 C      oo
                                                                                               18
Preventing Routing Updates through an
Interface
Load Balancing with RIP

				
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posted:9/15/2012
language:English
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