This post will deal with Multi-point redistribution and how to settle sub-optimal routing issues.

Topology.

Objective:

1. Configure redistribution between RIP and OSPF and vice-versa.
2. Settle the sub-optimal routing issues caused by the redistribution of routes.

Configurations:

Manila#sh run | sec ospf
router ospf 1
 network 11.11.11.11 0.0.0.0 area 1
 network 192.168.12.0 0.0.0.255 area 0
 network 192.168.13.0 0.0.0.255 area 0
 
 Hongkong#sh run | sec ospf
router ospf 1
 network 192.168.12.0 0.0.0.255 area 0

Hongkong#sh run | sec rip
router rip
 version 2
 network 22.0.0.0
 network 192.168.24.0
 no auto-summary
Hongkong#

Singapore#sh run | sec ospf
router ospf 1
 network 192.168.13.0 0.0.0.255 area 0

Singapore#sh run | sec rip
router rip
 version 2
 network 33.0.0.0
 network 192.168.35.0
 no auto-summary
Singapore#

Melbourne#sh run | sec rip
router rip
 version 2
 network 44.0.0.0
 network 192.168.24.0
 network 192.168.45.0
 no auto-summary
Melbourne#


Sydney#sh run | sec rip
router rip
 version 2
 network 55.0.0.0
 network 192.168.35.0
 network 192.168.45.0
 no auto-summary
Sydney#

Verifying the OSPF and RIP routes on Hongkong,

Hongkong#show ip route rip
!
Gateway of last resort is not set

      33.0.0.0/32 is subnetted, 1 subnets
R        33.33.33.33 [120/3] via 192.168.24.4, 00:00:17, Serial2/2
      44.0.0.0/32 is subnetted, 1 subnets
R        44.44.44.44 [120/1] via 192.168.24.4, 00:00:17, Serial2/2
      55.0.0.0/32 is subnetted, 1 subnets
R        55.55.55.55 [120/2] via 192.168.24.4, 00:00:17, Serial2/2
R     192.168.35.0/24 [120/2] via 192.168.24.4, 00:00:17, Serial2/2
R     192.168.45.0/24 [120/1] via 192.168.24.4, 00:00:17, Serial2/2

Hongkong#show ip route ospf
!
Gateway of last resort is not set

      11.0.0.0/32 is subnetted, 1 subnets
O IA     11.11.11.11 [110/65] via 192.168.12.1, 00:15:55, Serial2/0
O     192.168.13.0/24 [110/128] via 192.168.12.1, 00:15:58, Serial2/0
Hongkong#

Verifying the OSPF and RIP routes on Singapore.

Singapore#sh ip route rip
!
Gateway of last resort is not set

      22.0.0.0/32 is subnetted, 1 subnets
R        22.22.22.22 [120/3] via 192.168.35.5, 00:00:03, Serial2/2
      44.0.0.0/32 is subnetted, 1 subnets
R        44.44.44.44 [120/2] via 192.168.35.5, 00:00:03, Serial2/2
      55.0.0.0/32 is subnetted, 1 subnets
R        55.55.55.55 [120/1] via 192.168.35.5, 00:00:03, Serial2/2
R     192.168.24.0/24 [120/2] via 192.168.35.5, 00:00:03, Serial2/2
R     192.168.45.0/24 [120/1] via 192.168.35.5, 00:00:03, Serial2/2
Singapore#
 
 Singapore#sh ip route ospf
!
Gateway of last resort is not set

      11.0.0.0/32 is subnetted, 1 subnets
O IA     11.11.11.11 [110/65] via 192.168.13.1, 00:15:00, Serial2/1
O     192.168.12.0/24 [110/128] via 192.168.13.1, 00:15:00, Serial2/1
 Redistribution RIP into OSPF.

Hongkong(config)#router ospf 1
Hongkong(config-router)#redistribute rip subnets

Singapore(config)#router ospf 1
Singapore(config-router)#redistribute rip subnets

Here’s how the new OSPF configs looks like:

Hongkong#sh run | sec ospf
router ospf 1
 redistribute rip subnets
 network 192.168.12.0 0.0.0.255 area 0
Hongkong#
 
Singapore#sh run | sec ospf
router ospf 1
 redistribute rip subnets
 network 192.168.13.0 0.0.0.255 area 0
Singapore#


*** Without specifying the metrics, OSPF will used the defualt metric of 20****

The above redistribution’s of RIP into OSPF can be verified from the Manila Router as shown below.


Manila#show ip route ospf
!
Gateway of last resort is not set

      22.0.0.0/32 is subnetted, 1 subnets
O E2     22.22.22.22 [110/20] via 192.168.12.2, 00:02:09, Serial2/0
      33.0.0.0/32 is subnetted, 1 subnets
O E2     33.33.33.33 [110/20] via 192.168.13.3, 00:01:52, Serial2/1
      44.0.0.0/32 is subnetted, 1 subnets
O E2     44.44.44.44 [110/20] via 192.168.12.2, 00:02:09, Serial2/0
      55.0.0.0/32 is subnetted, 1 subnets
O E2     55.55.55.55 [110/20] via 192.168.12.2, 00:02:09, Serial2/0
O E2  192.168.24.0/24 [110/20] via 192.168.12.2, 00:02:09, Serial2/0
O E2  192.168.35.0/24 [110/20] via 192.168.13.3, 00:01:52, Serial2/1
O E2  192.168.45.0/24 [110/20] via 192.168.12.2, 00:02:09, Serial2/0
Manila#

*** All the routes redistributed into OSPF from any other routing protocol are considered as Type 5 External AS.


Redistributing OSPF into RIP:

Singapore(config)#router rip
Singapore(config-router)#redistribute ospf 1
Singapore(config-router)#default-metric 10

Hongkong(config)#router rip
Hongkong(config-router)#redistribute ospf 1
Hongkong(config-router)#default-metric 10

Here’s how the new RIP configs looks like ..

Hongkong#sh run | sec rip
router rip
 version 2
 redistribute ospf 1
 network 22.0.0.0
 network 192.168.24.0
 default-metric 10
 no auto-summary

Singapore#sh run | sec rip
router rip
 version 2
 redistribute ospf 1
 network 33.0.0.0
 network 192.168.35.0
 default-metric 10
 no auto-summary
Singapore#
 
 Checking Melbourne routes after the redistribution’s of OSPF into RIP:

Melbourne#show ip route rip
!
Gateway of last resort is not set

      11.0.0.0/32 is subnetted, 1 subnets
R        11.11.11.11 [120/10] via 192.168.24.2, 00:00:23, Serial2/2
      22.0.0.0/32 is subnetted, 1 subnets
R        22.22.22.22 [120/1] via 192.168.24.2, 00:00:23, Serial2/2
      33.0.0.0/32 is subnetted, 1 subnets
R        33.33.33.33 [120/2] via 192.168.45.5, 00:00:29, Serial2/0
      55.0.0.0/32 is subnetted, 1 subnets
R        55.55.55.55 [120/1] via 192.168.45.5, 00:00:29, Serial2/0
R     192.168.12.0/24 [120/10] via 192.168.24.2, 00:00:23, Serial2/2
R     192.168.13.0/24 [120/10] via 192.168.24.2, 00:00:23, Serial2/2
R     192.168.35.0/24 [120/1] via 192.168.45.5, 00:00:29, Serial2/0
Melbourne#

 ***The 3 routes that were added have a metrics of 10 ***

 Checking Sydney routes after the redistribution’s of OSPF into RIP:

 Sydney#show ip route rip
Codes: L – local, C – connected, S – static, R – RIP, M – mobile, B – BGP
!
Gateway of last resort is not set

      11.0.0.0/32 is subnetted, 1 subnets
R        11.11.11.11 [120/10] via 192.168.35.3, 00:00:01, Serial2/2
      22.0.0.0/32 is subnetted, 1 subnets
R        22.22.22.22 [120/2] via 192.168.45.4, 00:00:07, Serial2/0
      33.0.0.0/32 is subnetted, 1 subnets
R        33.33.33.33 [120/1] via 192.168.35.3, 00:00:01, Serial2/2
      44.0.0.0/32 is subnetted, 1 subnets
R        44.44.44.44 [120/1] via 192.168.45.4, 00:00:07, Serial2/0
R     192.168.12.0/24 [120/10] via 192.168.35.3, 00:00:01, Serial2/2
R     192.168.13.0/24 [120/10] via 192.168.35.3, 00:00:01, Serial2/2
R     192.168.24.0/24 [120/1] via 192.168.45.4, 00:00:07, Serial2/0
Sydney#

  ***The 3 routes that were added have a metrics of 10 ***

*** Sub-Optimal Routing Scenarios****

As observed from Singapore router, in order to reach Sydney network, it has to go through Manila –> Hongkong –> Melbourne —> Sydney, instead of just going directly from Singapore to Sydney via the direct link. This happens because of redistribution..

1.  RIP has an administrative distance of 120.

2. Since, I have redistributed RIP into OSPF, the RIP networks (in this case 55.55.55.55) were converted into an OSPF External Type 5 routes which has an AD of 110.  AD of 110 (OSPF)  is preferred over an AD of 120 ( RIP)

Singapore#show ip route ospf
!
Gateway of last resort is not set

      11.0.0.0/32 is subnetted, 1 subnets
O IA     11.11.11.11 [110/65] via 192.168.13.1, 00:37:34, Serial2/1
      22.0.0.0/32 is subnetted, 1 subnets
O E2     22.22.22.22 [110/20] via 192.168.13.1, 00:20:28, Serial2/1
      44.0.0.0/32 is subnetted, 1 subnets
O E2     44.44.44.44 [110/20] via 192.168.13.1, 00:20:28, Serial2/1
      55.0.0.0/32 is subnetted, 1 subnets
O E2     55.55.55.55 [110/20] via 192.168.13.1, 00:20:28, Serial2/1  <<< Sub-optimal routing
O     192.168.12.0/24 [110/128] via 192.168.13.1, 00:37:34, Serial2/1
O E2  192.168.24.0/24 [110/20] via 192.168.13.1, 00:20:28, Serial2/1
O E2  192.168.45.0/24 [110/20] via 192.168.13.1, 00:20:28, Serial2/1

 One of the method to settle sub-optimal routing is by changing the administrative distance.

1. Filter the routes via access-list of all the RIP routes.
2. Changed the AD of  the native RIP networks (current 120 to a higher value, e.g. 121 and above)

Singapore(config)#access-list 10 permit 192.168.24.0 0.0.0.255
Singapore(config)#access-list 10 permit 192.168.45.0 0.0.0.255
Singapore(config)#access-list 10 permit 192.168.35.0 0.0.0.255
Singapore(config)#access-list 10 permit 44.44.44.44 0.0.0.255
Singapore(config)#access-list 10 permit 55.55.55.55 0.0.0.255
Singapore(config)#access-list 10 permit 22.22.22.22 0.0.0.255
Singapore(config)#access-list 10 permit 33.33.33.33 0.0.0.255

Singapore(config)#router ospf 1
Singapore(config-router)#distance 121 0.0.0.0 255.255.255.255 10

 Now, the routes towards 55.55.55.55 has changed 

Singapore#show ip route | inc 55.55.55.55
R        55.55.55.55 [120/1] via 192.168.35.5, 00:00:29, Serial2/2
Singapore#

Singapore#traceroute 55.55.55.55
Type escape sequence to abort.
Tracing the route to 55.55.55.55
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.35.5 40 msec 52 msec 52 msec
Singapore#

Sub-optimal routing happens for 44.44.44.44 network on Melbourne as well.  Traffic path goes from Hongkong –> Manila –> Singapore –> Sydney — Melbourne .   The optimal path should be Hongkong –> Melbourne as per the topology.

Hongkong#show ip route 44.44.44.44
Routing entry for 44.44.44.44/32
  Known via “ospf 1”, distance 110, metric 20, type extern 2, forward metric 128
  Redistributing via rip
  Advertised by rip
  Last update from 192.168.12.1 on Serial2/0, 00:30:21 ago
  Routing Descriptor Blocks:
  * 192.168.12.1, from 33.33.33.33, 00:30:21 ago, via Serial2/0
      Route metric is 20, traffic share count is 1

Hongkong#traceroute 44.44.44.44
Type escape sequence to abort.
Tracing the route to 44.44.44.44
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.12.1 64 msec 52 msec 56 msec
  2 192.168.13.3 56 msec 52 msec 56 msec
  3 192.168.35.5 56 msec 56 msec 56 msec
  4 192.168.45.4 52 msec 56 msec 52 msec
Hongkong#


Hongkong(config)#access-list 10 permit 192.168.24.0 0.0.0.255
Hongkong(config)#access-list 10 permit 192.168.35.0 0.0.0.255
Hongkong(config)#access-list 10 permit 192.168.45.0 0.0.0.255
Hongkong(config)#access-list 10 permit 22.22.22.22 0.0.0.255
Hongkong(config)#access-list 10 permit 33.33.33.33 0.0.0.255
Hongkong(config)#access-list 10 permit 44.44.44.44 0.0.0.255
Hongkong(config)#access-list 10 permit 55.55.55.55 0.0.0.255
 Hongkong(config-router)#router ospf 1
Hongkong(config-router)#distance 121 0.0.0.0 255.255.255.255 10

 Now, the routes towards 44.44.44.44 has changed 

Hongkong#show ip route  | inc 44.44.44.44
R        44.44.44.44 [120/1] via 192.168.24.4, 00:00:25, Serial2/2
Hongkong#
 Hongkong#traceroute 44.44.44.44
Type escape sequence to abort.
Tracing the route to 44.44.44.44
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.24.4 60 msec 56 msec 72 msec
Hongkong#

**************************End of  Lab*************************************