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ospf distance manipulation

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Hey all

 

I am playing around with some redistribution and route manipulation (from Workbook 4 Lab 3, Task 4)

 

I have configured R1 to lower the distance to 105 for ospf LSA's specifically from router 2 (150.1.2.2) but it seems to include the same route that was advertised back fom R3 which is causing a feedback loop:

 

Rack1R1#show ip ospf data external 150.1.2.0

 

            OSPF Router with ID (150.1.1.1) (Process ID 1)

 

Type-5 AS External Link States

 

  Routing Bit Set on this LSA

  LS age: 1385

  Options: (No TOS-capability, DC)

  LS Type: AS External Link

  Link State ID: 150.1.2.0 (External Network Number )

  Advertising Router: 150.1.2.2

  LS Seq Number: 8000001A

  Checksum: 0x80D1

  Length: 36

  Network Mask: /24

Metric Type: 2 (Larger than any link state path)

TOS: 0 

Metric: 20 

Forward Address: 0.0.0.0

External Route Tag: 0

 

  Routing Bit Set on this LSA

  LS age: 1024

  Options: (No TOS-capability, DC)

  LS Type: AS External Link

  Link State ID: 150.1.2.0 (External Network Number )

  Advertising Router: 150.1.3.3

  LS Seq Number: 80000001

  Checksum: 0xA5C3

  Length: 36

  Network Mask: /24

Metric Type: 2 (Larger than any link state path)

TOS: 0 

Metric: 20 

Forward Address: 0.0.0.0

External Route Tag: 0

 

Rack1R1#sh ip route 150.1.2.2

Routing entry for 150.1.2.0/24

  Known via "ospf 1", distance 105, metric 20, type extern 2, forward metric 64

  Redistributing via rip

  Advertised by rip metric 8

  Last update from 163.1.12.2 on Serial0/2/0, 00:11:54 ago

  Routing Descriptor Blocks:

  * 163.1.13.3, from 150.1.3.3, 00:11:54 ago, via Serial0/1/0

      Route metric is 20, traffic share count is 1

    163.1.12.2, from 150.1.2.2, 00:11:54 ago, via Serial0/2/0

      Route metric is 20, traffic share count is 1

 

R1 config:

router ospf 1

 distance 105 150.1.2.2 0.0.0.0

router rip
 distance 109
I could fix this by changing the metric but I am curious as to why this is happening?  R1 redistributes 150.1.2.2 into RIP and also advertises it to R3 as OSPF.  R3 gets this from RIP (which it prefers) and redistributes it into OSPF and feeds it back to R1 casuing the loop.

Thanks

Nick


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