OSPF Inter-Area Summarization and Advertisements

Team,

I have one ABR between Area 0 and a standard Area 1, and I would like to summarize Area 1 addresses as they are passed into Area 0 on that ABR.

There is a particular prefix in Area 1 that is part of the summarized range, but I would like to advertise this particular more-specific prefix into Area 0 so that devices in Area 0 have both the summary address and this more-specific prefix in their routing tables.

How could I accomplish this task?

Thanks!

Comments

  • well are there any specific requirements? like this needs to be internal OSPF? can it be external ospf? since summarization can only happen at ABRs and ASBRs that can give you a possible solution. And there are two separate commands to summarise Internal OSPF and External OSPF. I don't want to give you the entire solution, but that most specifc prefix could be redistributed into OSPF rather than brought into OSPF with a  network command or a ip ospf 1 area x under the interface. Think about it and let us know.

  • I am running into the same thing, but since no one answered yet, I am still at a loss myself. [*-)] I have R6 w/ loopbacks configured that are running OSPF in area 46. R6 <> R4 are OSPF neighbors, with Area 0 and Area 46 on R4. I am trying to do summarization between these areas, but not summarize one of the subnets, something like an aggregate, with an unsuppress map but for OSPF. Requirements might be summarize between areas, use fewest lines as possible, which would make me to believe that you are not making several area range command for certain subnets?

    Rack1R6(config-if)#do sh run int lo2
    Building configuration...

    Current configuration : 114 bytes
    !
    interface Loopback2
     ip address 183.1.2.1 255.255.255.0
     ip ospf network point-to-point
     ip ospf 1 area 46
    end

    Rack1R6(config-if)#do sh run int lo7
    Building configuration...

    Current configuration : 114 bytes
    !
    interface Loopback4
     ip address 183.1.7.1 255.255.255.0
     ip ospf network point-to-point
     ip ospf 1 area 46
    end

    Rack1R6(config-if)#do sh run int lo12
    Building configuration...

    Current configuration : 116 bytes
    !
    interface Loopback12
     ip address 183.1.12.1 255.255.255.0
     ip ospf network point-to-point
     ip ospf 1 area 46
    end

    Rack1R6(config-if)#do sh run int lo14
    Building configuration...

    Current configuration : 116 bytes
    !
    interface Loopback14
     ip address 183.1.14.1 255.255.255.0
     ip ospf network point-to-point
     ip ospf 1 area 46
    end

    Rack1R4(config-router)#do sh run | b router ospf
    router ospf 1
     router-id 150.1.4.4
     log-adjacency-changes detail
     area 45 virtual-link 150.1.5.5
     area 46 range 183.1.2.0 255.255.255.0 not-advertise
     area 46 range 183.1.0.0 255.255.240.0
     network 150.1.4.4 0.0.0.0 area 0
     network 183.1.0.4 0.0.0.0 area 0
     network 183.1.45.4 0.0.0.0 area 45
     network 183.1.46.4 0.0.0.0 area 46

    R4 see all of these as /24s in routing table, but I only see one LSA-type3 for 183.1.0.0/20

    Rack1R4(config-router)#do sh ip route 183.1.2.0
    Routing entry for 183.1.2.0/24
      Known via "ospf 1", distance 110, metric 11, type intra area
      Last update from 183.1.46.6 on FastEthernet0/1, 00:01:43 ago
      Routing Descriptor Blocks:
      * 183.1.46.6, from 150.1.6.6, 00:01:43 ago, via FastEthernet0/1
          Route metric is 11, traffic share count is 1

    Rack1R4(config-router)#do sh ip route 183.1.7.0
    Routing entry for 183.1.7.0/24
      Known via "ospf 1", distance 110, metric 11, type intra area
      Last update from 183.1.46.6 on FastEthernet0/1, 00:01:46 ago
      Routing Descriptor Blocks:
      * 183.1.46.6, from 150.1.6.6, 00:01:46 ago, via FastEthernet0/1
          Route metric is 11, traffic share count is 1

    Rack1R4(config-router)#do sh ip route 183.1.12.0
    Routing entry for 183.1.12.0/24
      Known via "ospf 1", distance 110, metric 11, type intra area
      Last update from 183.1.46.6 on FastEthernet0/1, 00:01:49 ago
      Routing Descriptor Blocks:
      * 183.1.46.6, from 150.1.6.6, 00:01:49 ago, via FastEthernet0/1
          Route metric is 11, traffic share count is 1

    Rack1R4(config-router)#do sh ip route 183.1.14.0
    Routing entry for 183.1.14.0/24
      Known via "ospf 1", distance 110, metric 11, type intra area
      Last update from 183.1.46.6 on FastEthernet0/1, 00:01:52 ago
      Routing Descriptor Blocks:
      * 183.1.46.6, from 150.1.6.6, 00:01:52 ago, via FastEthernet0/1
          Route metric is 11, traffic share count is 1

     Rack1R4(config-router)#do sh ip ospf 1 0 data summ | b 183.1.0.0
      Link State ID: 183.1.0.0 (summary Network Number)
      Advertising Router: 150.1.4.4
      LS Seq Number: 80000001
      Checksum: 0xC424
      Length: 28
      Network Mask: /20
            TOS: 0  Metric: 11

    R4 <> R5 area OSPF neighbors but R5 sees this summary as a type-3 LSA for 183.1.0.0/20, but I don't see the more specific 183.1.2.0/24 that I said 'no-advertise' with? I was assuming that all is summarized except what you specific with 'no-advertise'. Is this not correct?

    R5 sees all of these as the /20 summary?

    Rack1R5(config-if)#do sh ip route 183.1.2.0
    Routing entry for 183.1.0.0/20
      Known via "ospf 1", distance 110, metric 76, type inter area
      Redistributing via eigrp 100
      Advertised by eigrp 100 route-map OSPF-TO-EIGRP100
      Last update from 183.1.0.4 on Serial0/0, 00:00:22 ago
      Routing Descriptor Blocks:
      * 183.1.0.4, from 150.1.4.4, 00:00:22 ago, via Serial0/0
          Route metric is 76, traffic share count is 1

    Rack1R5(config-if)#do sh ip route 183.1.7.0
    Routing entry for 183.1.0.0/20
      Known via "ospf 1", distance 110, metric 76, type inter area
      Redistributing via eigrp 100
      Advertised by eigrp 100 route-map OSPF-TO-EIGRP100
      Last update from 183.1.0.4 on Serial0/0, 00:00:27 ago
      Routing Descriptor Blocks:
      * 183.1.0.4, from 150.1.4.4, 00:00:27 ago, via Serial0/0
          Route metric is 76, traffic share count is 1

    Rack1R5(config-if)#do sh ip route 183.1.12.0
    Routing entry for 183.1.0.0/20
      Known via "ospf 1", distance 110, metric 76, type inter area
      Redistributing via eigrp 100
      Advertised by eigrp 100 route-map OSPF-TO-EIGRP100
      Last update from 183.1.0.4 on Serial0/0, 00:00:32 ago
      Routing Descriptor Blocks:
      * 183.1.0.4, from 150.1.4.4, 00:00:32 ago, via Serial0/0
          Route metric is 76, traffic share count is 1

    Rack1R5(config-if)#do sh ip route 183.1.14.0
    Routing entry for 183.1.0.0/20
      Known via "ospf 1", distance 110, metric 76, type inter area
      Redistributing via eigrp 100
      Advertised by eigrp 100 route-map OSPF-TO-EIGRP100
      Last update from 183.1.0.4 on Serial0/0, 00:00:41 ago
      Routing Descriptor Blocks:
      * 183.1.0.4, from 150.1.4.4, 00:00:41 ago, via Serial0/0
          Route metric is 76, traffic share count is 1

    Rack1R5(config-if)#do sh ip ospf 1 0 data summ | b 183.1.0.0
      Link State ID: 183.1.0.0 (summary Network Number)
      Advertising Router: 150.1.4.4
      LS Seq Number: 80000001
      Checksum: 0xC424
      Length: 28
      Network Mask: /20
            TOS: 0  Metric: 11

    with none for 183.1.2.0/24?

    Is there a way to advertise a summary, and include more specific prefixes in OSPF? Please help clarify as I am confused...thanks!

    -D

  • If you want to summarize Type 3 LSA and allow more specific routes to be injected, then you need to use advertise keyword and you are using no-advertise ... see example below:

    Topology - R2----OSPF----R1-----OSPF-----R3

    R2 - Injecting routes 10.1.1.0/24, 10.1.2.0/24, 10.1.3.0/24 into OSPF area 0

    router ospf 1
     log-adjacency-changes
     network 10.1.1.1 0.0.0.0 area 0
     network 10.1.2.1 0.0.0.0 area 0
     network 10.1.3.1 0.0.0.0 area 0
     network 155.1.12.2 0.0.0.0 area 0

     

    R1 - receives this routes as /24 Intra-area networks

    R1#sh ip route os
         10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
    O       10.1.3.0/24 [110/11] via 155.1.12.2, 00:03:28, FastEthernet0/0
    O       10.1.2.0/24 [110/11] via 155.1.12.2, 00:03:28, FastEthernet0/0
    O       10.1.1.0/24 [110/11] via 155.1.12.2, 00:03:28, FastEthernet0/0

    R1 - summarize them into /22 network and advertise 10.1.3.0/24 (which is part of the summary)

    router ospf 1
     log-adjacency-changes
     area 0 range 10.1.3.0 255.255.255.0
     area 0 range 10.1.0.0 255.255.252.0

     network 155.1.12.1 0.0.0.0 area 0
     network 155.1.13.1 0.0.0.0 area 13

    R3 - results

    R3#sh ip route ospf

         10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    O IA    10.1.3.0/24 [110/21] via 155.1.13.1, 00:00:02, FastEthernet0/0
    O IA    10.1.0.0/22 [110/21] via 155.1.13.1, 00:00:20, FastEthernet0/0
    R3#

    Area range does not use route-maps (unfortunately) like BGP aggregate command to use single line for suppressing/unsuppressing networks. You have to use multiple lines in your case to leak more specific networks into OSPF.

    HTH

     

    I am running into the same thing, but since no one answered yet, I am still at a loss myself. Confused I have R6 w/ loopbacks configured that are running OSPF in area 46. R6 <> R4 are OSPF neighbors, with Area 0 and Area 46 on R4. I am trying to do summarization between these areas, but not summarize one of the subnets, something like an aggregate, with an unsuppress map but for OSPF. Requirements might be summarize between areas, use fewest lines as possible, which would make me to believe that you are not making several area range command for certain subnets?

    Rack1R6(config-if)#do sh run int lo2
    Building configuration...

    Current configuration : 114 bytes
    !
    interface Loopback2
     ip address 183.1.2.1 255.255.255.0
     ip ospf network point-to-point
     ip ospf 1 area 46
    end

    Rack1R6(config-if)#do sh run int lo7
    Building configuration...

    Current configuration : 114 bytes
    !
    interface Loopback4
     ip address 183.1.7.1 255.255.255.0
     ip ospf network point-to-point
     ip ospf 1 area 46
    end

    Rack1R6(config-if)#do sh run int lo12
    Building configuration...

    Current configuration : 116 bytes
    !
    interface Loopback12
     ip address 183.1.12.1 255.255.255.0
     ip ospf network point-to-point
     ip ospf 1 area 46
    end

    Rack1R6(config-if)#do sh run int lo14
    Building configuration...

    Current configuration : 116 bytes
    !
    interface Loopback14
     ip address 183.1.14.1 255.255.255.0
     ip ospf network point-to-point
     ip ospf 1 area 46
    end

    Rack1R4(config-router)#do sh run | b router ospf
    router ospf 1
     router-id 150.1.4.4
     log-adjacency-changes detail
     area 45 virtual-link 150.1.5.5
     area 46 range 183.1.2.0 255.255.255.0 not-advertise
     area 46 range 183.1.0.0 255.255.240.0
     network 150.1.4.4 0.0.0.0 area 0
     network 183.1.0.4 0.0.0.0 area 0
     network 183.1.45.4 0.0.0.0 area 45
     network 183.1.46.4 0.0.0.0 area 46

    R4 see all of these as /24s in routing table, but I only see one LSA-type3 for 183.1.0.0/20

    Rack1R4(config-router)#do sh ip route 183.1.2.0
    Routing entry for 183.1.2.0/24
      Known via "ospf 1", distance 110, metric 11, type intra area
      Last update from 183.1.46.6 on FastEthernet0/1, 00:01:43 ago
      Routing Descriptor Blocks:
      * 183.1.46.6, from 150.1.6.6, 00:01:43 ago, via FastEthernet0/1
          Route metric is 11, traffic share count is 1

    Rack1R4(config-router)#do sh ip route 183.1.7.0
    Routing entry for 183.1.7.0/24
      Known via "ospf 1", distance 110, metric 11, type intra area
      Last update from 183.1.46.6 on FastEthernet0/1, 00:01:46 ago
      Routing Descriptor Blocks:
      * 183.1.46.6, from 150.1.6.6, 00:01:46 ago, via FastEthernet0/1
          Route metric is 11, traffic share count is 1

    Rack1R4(config-router)#do sh ip route 183.1.12.0
    Routing entry for 183.1.12.0/24
      Known via "ospf 1", distance 110, metric 11, type intra area
      Last update from 183.1.46.6 on FastEthernet0/1, 00:01:49 ago
      Routing Descriptor Blocks:
      * 183.1.46.6, from 150.1.6.6, 00:01:49 ago, via FastEthernet0/1
          Route metric is 11, traffic share count is 1

    Rack1R4(config-router)#do sh ip route 183.1.14.0
    Routing entry for 183.1.14.0/24
      Known via "ospf 1", distance 110, metric 11, type intra area
      Last update from 183.1.46.6 on FastEthernet0/1, 00:01:52 ago
      Routing Descriptor Blocks:
      * 183.1.46.6, from 150.1.6.6, 00:01:52 ago, via FastEthernet0/1
          Route metric is 11, traffic share count is 1

     Rack1R4(config-router)#do sh ip ospf 1 0 data summ | b 183.1.0.0
      Link State ID: 183.1.0.0 (summary Network Number)
      Advertising Router: 150.1.4.4
      LS Seq Number: 80000001
      Checksum: 0xC424
      Length: 28
      Network Mask: /20
            TOS: 0  Metric: 11

    R4 <> R5 area OSPF neighbors but R5 sees this summary as a type-3 LSA for 183.1.0.0/20, but I don't see the more specific 183.1.2.0/24 that I said 'no-advertise' with? I was assuming that all is summarized except what you specific with 'no-advertise'. Is this not correct?

    R5 sees all of these as the /20 summary?

    Rack1R5(config-if)#do sh ip route 183.1.2.0
    Routing entry for 183.1.0.0/20
      Known via "ospf 1", distance 110, metric 76, type inter area
      Redistributing via eigrp 100
      Advertised by eigrp 100 route-map OSPF-TO-EIGRP100
      Last update from 183.1.0.4 on Serial0/0, 00:00:22 ago
      Routing Descriptor Blocks:
      * 183.1.0.4, from 150.1.4.4, 00:00:22 ago, via Serial0/0
          Route metric is 76, traffic share count is 1

    Rack1R5(config-if)#do sh ip route 183.1.7.0
    Routing entry for 183.1.0.0/20
      Known via "ospf 1", distance 110, metric 76, type inter area
      Redistributing via eigrp 100
      Advertised by eigrp 100 route-map OSPF-TO-EIGRP100
      Last update from 183.1.0.4 on Serial0/0, 00:00:27 ago
      Routing Descriptor Blocks:
      * 183.1.0.4, from 150.1.4.4, 00:00:27 ago, via Serial0/0
          Route metric is 76, traffic share count is 1

    Rack1R5(config-if)#do sh ip route 183.1.12.0
    Routing entry for 183.1.0.0/20
      Known via "ospf 1", distance 110, metric 76, type inter area
      Redistributing via eigrp 100
      Advertised by eigrp 100 route-map OSPF-TO-EIGRP100
      Last update from 183.1.0.4 on Serial0/0, 00:00:32 ago
      Routing Descriptor Blocks:
      * 183.1.0.4, from 150.1.4.4, 00:00:32 ago, via Serial0/0
          Route metric is 76, traffic share count is 1

    Rack1R5(config-if)#do sh ip route 183.1.14.0
    Routing entry for 183.1.0.0/20
      Known via "ospf 1", distance 110, metric 76, type inter area
      Redistributing via eigrp 100
      Advertised by eigrp 100 route-map OSPF-TO-EIGRP100
      Last update from 183.1.0.4 on Serial0/0, 00:00:41 ago
      Routing Descriptor Blocks:
      * 183.1.0.4, from 150.1.4.4, 00:00:41 ago, via Serial0/0
          Route metric is 76, traffic share count is 1

    Rack1R5(config-if)#do sh ip ospf 1 0 data summ | b 183.1.0.0
      Link State ID: 183.1.0.0 (summary Network Number)
      Advertising Router: 150.1.4.4
      LS Seq Number: 80000001
      Checksum: 0xC424
      Length: 28
      Network Mask: /20
            TOS: 0  Metric: 11

    with none for 183.1.2.0/24?

    Is there a way to advertise a summary, and include more specific prefixes in OSPF? Please help clarify as I am confused...thanks!

    -D

     

  • K, I see what i was doing. Once I removed the 'not-advertise' i got the results that i was looking for. So in essence the only way to create a summary and leak more specifics of that summary is to just add another summary with 'area range'command if the limitation is staying to inter-area summaries. Thanks for opening my eyes on how this command works.

    -D

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