Routing

1
Routing

• Route Redistribution

2
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?

3
Complex Routing designs in enterprises

• 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

4
Migration

• 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

5
Routing Process
RIP
OSPF

• Routers within one routing instance typically run
  the same routing protocol to fully share
  reachability information
• do not exchange routing information with routers
  in other routing instances
• Figure 1. It consists of two routing instances.
• Routers in the RIP instance do not have
  visibility of the addresses and subnet prefixes
  in the OSPF instance and vice versa.

D
A
G
B
F
E
C
H
6
Route redistribution

• 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.

7
Default Seed Metrics
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
8
Planning Redistribution

• 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.

9
Example Redistribution into OSPF
RtrA(config) router ospf 1RtrA(config-router)
redistribute eigrp ? lt1-65535gt 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 ltcrgt
10
Redistributing with seed metric

• 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.

11
Redistributing into OSPF
12
Redistributing into EIGRP

• Bandwidth in kilobytes 10000
• Delay in tens of microseconds 100
• Reliability 255 (maximum)
• Load 1 (minimum)
• MTU 1,500 bytes

13
Example Before Redistribution
14
Example Before Redistribution (Cont.)
15
Example Configuring Redistribution at Router B
16
Example Routing Tables After Route Redistribution
17
Example Routing Tables After Summarizing Routes
and Redistributions
18
Example Redistribution Using Administrative
Distance
19
Example Redistribution Using Administrative
Distance (Cont.)
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 P3R1
router ospf 1 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
Router P3R2
20
Example Redistribution Using Administrative
Distance (Cont.)
21
Example Redistribution Using Administrative
Distance (Cont.)

hostname P3R1 ! router ospf 1 redistribute rip
metric 10000 metric-type 1 subnets network
172.31.0.0 0.0.255.255 area 0 distance 125
0.0.0.0 255.255.255.255 64 ! router rip version
2 redistribute ospf 1 metric 5 network
10.0.0.0 no auto-summary !
hostname P3R2 ! router ospf 1 redistribute rip
metric 10000 metric-type 1 subnets network
172.31.3.2 0.0.0.0 area 0 distance 125 0.0.0.0
255.255.255.255 64 ! router rip version 2
redistribute ospf 1 metric 5 network 10.0.0.0
no auto-summary !
22
Example Redistribution Using Administrative
Distance (Cont.)

hostname P3R1 ! router ospf 1 redistribute rip
metric 10000 metric-type 1 subnets network
172.31.0.0 0.0.255.255 area 0 distance 125
0.0.0.0 255.255.255.255 64 ! router rip version
2 redistribute ospf 1 metric 5 network
10.0.0.0 no auto-summary !
hostname P3R2 ! router ospf 1 redistribute rip
metric 10000 metric-type 1 subnets network
172.31.3.2 0.0.0.0 area 0 distance 125 0.0.0.0
255.255.255.255 64 ! router rip version 2
redistribute ospf 1 metric 5 network 10.0.0.0
no auto-summary !
23
Example Redistribution Using Administrative
Distance (Cont.)
24
Know Your Network

• 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