CCNP route workbook Redistribution Adv Lab 1

Guys,

 

I need some help understanding this behavior on r4.

 

R4#sh ip route 10.10.10.10
Routing entry for 10.10.10.10/32
  Known via "eigrp 100", distance 170, metric 2565120, type external
  Redistributing via eigrp 100, ospf 1
  Advertised by ospf 1 metric 200 subnets
  Last update from 10.1.14.1 on FastEthernet0/1.14, 00:00:02 ago
  Routing Descriptor Blocks:
  * 10.1.14.1, from 10.1.14.1, 00:00:02 ago, via FastEthernet0/1.14
      Route metric is 2565120, traffic share count is 1
      Total delay is 200 microseconds, minimum bandwidth is 1000 Kbit
      Reliability 255/255, minimum MTU 1500 bytes
      Loading 1/255, Hops 1
R4#sh ip ospf database external 10.10.10.10

            OSPF Router with ID (4.4.4.4) (Process ID 1)

               Type-5 AS External Link States

  LS age: 60
  Options: (No TOS-capability, DC, Upward)
  LS Type: AS External Link
  Link State ID: 10.10.10.10 (External Network Number )
  Advertising Router: 4.4.4.4
  LS Seq Number: 80000001
  Checksum: 0xB003
  Length: 36
  Network Mask: /32
           Metric Type: 2 (Larger than any link state path)
           MTID: 0
           Metric: 200
           Forward Address: 0.0.0.0
           External Route Tag: 0

 

The above shows when r4 redistributes eigrp to ospf. So we can see the type 5 LSA that gets created and when you do sh ip route, the IOS/routing daemon tells you this was learn via eigrp and it is redistributing the same to ospf. And this I believe is also what prevents the routing daemon to look at this type for lsa in isolation and say, let me pick this for RIB on this router as OSPF AD is better than eigrp external, etc. So far so good.

When i now redistribute eigrp to ospf from another border router, that is when routing loop happens. I get the concept in theory. But i want to understand one change in lsdb on r4.

 

R4#sh ip ospf database external 10.10.10.10

            OSPF Router with ID (4.4.4.4) (Process ID 1)

               Type-5 AS External Link States

  Routing Bit Set on this LSA in topology Base with MTID 0
  LS age: 8
  Options: (No TOS-capability, DC, Upward)
  LS Type: AS External Link
  Link State ID: 10.10.10.10 (External Network Number )
  Advertising Router: 2.2.2.2
  LS Seq Number: 80000001
  Checksum: 0xD77F
  Length: 36
  Network Mask: /32
           Metric Type: 2 (Larger than any link state path)
           MTID: 0
           Metric: 300
           Forward Address: 0.0.0.0
           External Route Tag: 0

  Delete flag is set for this LSA
  LS age: MAXAGE(3602)
  Options: (No TOS-capability, DC, Upward)
  LS Type: AS External Link
  Link State ID: 10.10.10.10 (External Network Number )
  Advertising Router: 4.4.4.4
  LS Seq Number: 80000002
  Checksum: 0xD6A4
  Length: 36
  Network Mask: /32
           Metric Type: 2 (Larger than any link state path)
           MTID: 0
           Metric: 16777215
           Forward Address: 0.0.0.0
           External Route Tag: 0

 

When R2 starts advertising the same from ospf as it was redistributed into it via eigrp. R4 deletest the type lsa it self originated and accepts the lsa generated by 2.2.2.2. WHY? doesn't matter how bad i make this metric from 2.2.2.2. R4 still takes it and deletes the LSA it generated.

I think understading this will solve the mystery and tell me why exactly we see loops.

 

Thanks

Comments

  • opps.. never mind . this is not ccie rs redistribution wb;

    let me see if i can find ccnp wb. ..

     

Sign In or Register to comment.