Docstoc

Routing

Document Sample
Routing Powered By Docstoc
					Route Redistribution
 What  is route redistribution?
 Why is it required in network?
 Where is it implemented in the
  network?
 How is it implemented
 Problems due to route
  redistribution?
   routing structure of a large enterprise network
    typically consists of multiple domains or routing
    instances due to:
    ◦ Company acquisitions
    ◦ departments administered by different teams
    ◦ multi-vendor equipments
    ◦ Intentional creation of separate routing instances to
       filter routes
       limit reachability and
       enforce policies
   Careful and thoughtful migration from one
    routing protocol to another
   The new routing protocol will most likely
    have different requirements and capabilities
    from the old one.
    It is important for network administrators to
    understand what must be changed and to
    create a detailed plan before making any
    changes
                                             RIP           OSPF
   Routers within one routing
    instance typically run the same
    routing protocol to fully share
    reachability information
                                                   A   D    G
    do not exchange routing
    information with routers in
    other routing instances                  B                    F
   Figure 1. It consists of two
    routing instances.                                 E
                                                   C
    ◦ Routers in the RIP instance do not                    H
      have visibility of the addresses and
      subnet prefixes in the OSPF instance
      and vice versa.
•   Each routing protocol defines a metric for each
    route.
    • RIP – 120, OSPF – 110, EIGRP - 90
•   When a router redistributes routes from one routing
    domain to another this information cannot be
    translated from one routing protocol to another.
    • A RIP hop cannot be dynamically recalculated to an
      OSPF cost by the router doing redistribution.
•   A seed metric is used to artificially set the distance,
    cost, etc., to each redistributed network from the
    redistribution point.
Protocol     Default Seed Metrics
RIP          Infinity
IGRP/EIGRP Infinity
OSPF         20 for all except BGP, which is 1
IS-IS        0
BGP          BGP metric is set to IGP metric value
   Locate the boundary router between two routing processes.
   Determine which routing process is the core or backbone
    process
   Determine which routing process is the edge or migration
    process
   Select a method for injecting the required edge protocol
    routes into the core.
RtrA(config)# router ospf 1
RtrA(config-router)# redistribute eigrp ?

  <1-65535> Autonomous system number
RtrA(config-router)# redistribute eigrp 100 ?

  metric         Metric for redistributed routes
  metric-type    OSPF/IS-IS exterior metric type for
redistributed routes
  route-map      Route map reference
  subnets        Consider subnets for redistribution into OSPF
  tag            Set tag for routes redistributed into OSPF
  …
  <cr>
   Router C is using a seed metric of 30 inside the OSPF routing
    process to redistributed RIP routes.
    ◦ ROUTER C (config-router) redistribute rip subnets metric 30.
   The link cost of the WAN link to router D is 100.
   The cost for networks 1.0.0.0, 2.0.0.0, and 3.0.0.0 in router D is the
    seed metric (30) plus the link cost (100) = 130.
   Bandwidth in kilobytes = 10000
   Delay in tens of microseconds = 100
   Reliability = 255 (maximum)
   Load = 1 (minimum)
   MTU = 1,500 bytes
Router P3R1   router ospf 1
               redistribute rip metric 10000 metric-type 1 subnets
               network 172.31.0.0 0.0.255.255 area 0
              !
              router rip
               version 2
               redistribute ospf 1 metric 5
               network 10.0.0.0
               no auto-summary


              router ospf 1
Router P3R2    redistribute rip metric 10000 metric-type 1 subnets
               network 172.31.3.2 0.0.0.0 area 0
              !
              router rip
               version 2
               redistribute ospf 1 metric 5
               network 10.0.0.0
               no auto-summary
hostname P3R1                      hostname P3R2
!                                  !
router ospf 1                      router ospf 1
  redistribute rip metric 10000    redistribute rip metric 10000
metric-type 1 subnets              metric-type 1 subnets
  network 172.31.0.0 0.0.255.255     network 172.31.3.2 0.0.0.0 area 0
area 0                               distance 125 0.0.0.0
  distance 125 0.0.0.0             255.255.255.255 64
255.255.255.255 64                 !
!                                  router rip
router rip                           version 2
  version 2                          redistribute ospf 1 metric 5
  redistribute ospf 1 metric 5       network 10.0.0.0
  network 10.0.0.0                   no auto-summary
  no auto-summary                  !
!
hostname P3R1                      hostname P3R2
!                                  !
router ospf 1                      router ospf 1
  redistribute rip metric 10000    redistribute rip metric 10000
metric-type 1 subnets              metric-type 1 subnets
  network 172.31.0.0 0.0.255.255     network 172.31.3.2 0.0.0.0 area 0
area 0                               distance 125 0.0.0.0
  distance 125 0.0.0.0             255.255.255.255 64
255.255.255.255 64                 !
!                                  router rip
router rip                           version 2
  version 2                          redistribute ospf 1 metric 5
  redistribute ospf 1 metric 5       network 10.0.0.0
  network 10.0.0.0                   no auto-summary
  no auto-summary                  !
!
   Be very familiar with
    your network BEFORE
    implementing
    redistribution
   Focus on routers with
    redundant paths
   Make sure no path
    information is lost
    when using the
    distance command

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:3
posted:9/10/2012
language:English
pages:24