Problem with prefix list to filter networks on ospf.

[Erico Verissimo]

Hi there! Good Morning

I have a problem when I had applied the prefix-list on ospf. The network 10.206.2.0/27 don't enter on the rib.

follow the configuration:

Before prefix-list in:

#sh ip route 10.206.2.0
Routing entry for 10.206.2.0/27
  Known via "ospf 100", distance 110, metric 48952, type extern 1
  Last update from 192.168.162.77 on GigabitEthernet0/1, 14:13:02 ago
  Routing Descriptor Blocks:
  * 192.168.162.77, from 10.206.0.10, 14:13:02 ago, via GigabitEthernet0/1
      Route metric is 48952, traffic share count is 1

Prefix-list applied:

router ospf 100
 router-id 10.221.2.1
 log-adjacency-changes
 auto-cost reference-bandwidth 100000
 passive-interface GigabitEthernet0/0
 network 0.0.0.0 255.255.255.255 area 0
 distribute-list prefix filter_ospf in

ip prefix-list filter_ospf description Aplicacoes
ip prefix-list filter_ospf seq 10 permit 0.0.0.0/0
ip prefix-list filter_ospf seq 20 permit 10.98.0.0/28
ip prefix-list filter_ospf seq 30 permit 10.100.0.0/16
ip prefix-list filter_ospf seq 40 permit 10.206.0.0/16 le 24
ip prefix-list filter_ospf seq 50 permit 10.206.2.0/27
ip prefix-list filter_ospf seq 60 permit 10.208.0.0/16 le 24
ip prefix-list filter_ospf seq 70 permit 10.254.0.0/24 le 27
ip prefix-list filter_ospf seq 200 deny 0.0.0.0/0 le 32

After prefix-list in:

#sh ip route 10.206.2.0
% Subnet not in table

All other prefixes are filtrated after putt the prefix-list on ospf, only network 10.206.2.0 don't appear in the sh ip route command.

Thank's and sorry about my english!! I'm learning it.

[Vasilii Mikhailovskii · Accepted solution]

Hello.

Please check if you have the prefix in ospf rib - show ip ospf rib ...

and check if you have the prefix in LSDB - show ip ospf data ext ... + show ip ospf border

(you might have filtered out forwarding address)

[Erico Verissimo]

Vasilii,

Thank's for your answer. I did the test, apply the prefix again, and now I paid atention in the Forward Address, yes I just blocked this network. I put this network on permit like below:

#sh ip ospf database external 10.206.2.0

            OSPF Router with ID (10.221.2.1) (Process ID 100)

                Type-5 AS External Link States

  LS age: 329
  Options: (No TOS-capability, DC)
  LS Type: AS External Link
  Link State ID: 10.206.2.0 (External Network Number )
  Advertising Router: 10.206.0.10
  LS Seq Number: 80004E19
  Checksum: 0xC5B7
  Length: 36
  Network Mask: /27
        Metric Type: 1 (Comparable directly to link state metric)
        MTID: 0 
        Metric: 20 
        Forward Address: 10.127.1.20
        External Route Tag: 0

ip prefix-list filter_ospf seq 25 permit 10.127.1.16/28

Now it works perfectly, thank's so much!!!