OSPF Summarization

Here is the following scenario:

First let's divide the routers according to their role:

R1 is an internal router in area 1

R2 and R4 are ABR and backbone routers for areas 1 and 5

R3 is a backbone and internal router (area 0 only)

R5 is an ABR router for areas 5 and 6

R6 is an ASBR and internal router for area 6

So first thing projected from this diagram is that R6 must have connection to area 0 as an OSPF mandatory requirement.

Note that although I have configured R5 and R6 and they are adjacent neighbors, R5 can see R6 redistributed routes but all other routers won’t.

R5#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface

R4                1   FULL/DR         00:00:33    10.1.45.4       FastEthernet0/0

R6                1   FULL/BDR        00:00:34    10.1.56.6       FastEthernet0/1

 R5#show ip route ospf

     1.0.0.0/32 is subnetted, 1 subnets

O IA    1.1.1.1 [110/41] via 10.1.45.4, 00:15:23, FastEthernet0/0

     2.0.0.0/32 is subnetted, 1 subnets

O IA    2.2.2.2 [110/31] via 10.1.45.4, 00:15:23, FastEthernet0/0

     3.0.0.0/32 is subnetted, 1 subnets

O IA    3.3.3.3 [110/21] via 10.1.45.4, 00:17:34, FastEthernet0/0

O IA 192.168.30.0/24 [110/41] via 10.1.45.4, 00:15:23, FastEthernet0/0

     4.0.0.0/32 is subnetted, 1 subnets

O IA    4.4.4.4 [110/11] via 10.1.45.4, 00:17:34, FastEthernet0/0

O IA 192.168.10.0/24 [110/41] via 10.1.45.4, 00:15:23, FastEthernet0/0

O IA 192.168.40.0/24 [110/41] via 10.1.45.4, 00:15:23, FastEthernet0/0

     6.0.0.0/32 is subnetted, 1 subnets

O       6.6.6.6 [110/11] via 10.1.56.6, 00:17:34, FastEthernet0/1

     172.16.0.0/24 is subnetted, 4 subnets

O E2    172.16.4.0 [110/20] via 10.1.56.6, 00:15:18, FastEthernet0/1

O E2    172.16.1.0 [110/20] via 10.1.56.6, 00:15:18, FastEthernet0/1

O E2    172.16.2.0 [110/20] via 10.1.56.6, 00:15:18, FastEthernet0/1

O E2    172.16.3.0 [110/20] via 10.1.56.6, 00:15:19, FastEthernet0/1

O IA 192.168.20.0/24 [110/41] via 10.1.45.4, 00:15:24, FastEthernet0/0

     10.0.0.0/24 is subnetted, 5 subnets

O IA    10.1.12.0 [110/40] via 10.1.45.4, 00:15:24, FastEthernet0/0

O IA    10.1.23.0 [110/30] via 10.1.45.4, 00:17:35, FastEthernet0/0

O IA    10.1.34.0 [110/20] via 10.1.45.4, 00:17:35, FastEthernet0/0

So I have configured a virtual-link between R5, which has interface in area 6, to R4 which has interface in area 0.

R4:

R4(config)#router ospf 1

R4(config-router)#area 5 virtual-link 5.5.5.5

And R5:

R5(config)#router ospf 1

R5(config-router)#area 5 virtual-link 4.4.4.4

Note that virtual-link must be configured using router-id and based on the transit area which in this case is area 5, else we will get the following message:

*Mar  1 00:45:20.235: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 10.1.45.5, FastEthernet0/1

Now looking on R3 routing table we can see quite few lines:

R3#sh ip route ospf

     1.0.0.0/32 is subnetted, 1 subnets

O IA    1.1.1.1 [110/21] via 10.1.23.2, 00:06:49, FastEthernet0/0

     2.0.0.0/32 is subnetted, 1 subnets

O       2.2.2.2 [110/11] via 10.1.23.2, 00:06:49, FastEthernet0/0

O IA 192.168.30.0/24 [110/21] via 10.1.23.2, 00:06:49, FastEthernet0/0

     4.0.0.0/32 is subnetted, 1 subnets

O       4.4.4.4 [110/11] via 10.1.34.4, 00:06:49, FastEthernet0/1

     5.0.0.0/32 is subnetted, 1 subnets

O IA    5.5.5.5 [110/21] via 10.1.34.4, 00:06:49, FastEthernet0/1

O IA 192.168.10.0/24 [110/21] via 10.1.23.2, 00:06:49, FastEthernet0/0

O IA 192.168.40.0/24 [110/21] via 10.1.23.2, 00:06:49, FastEthernet0/0

     6.0.0.0/32 is subnetted, 1 subnets

O IA    6.6.6.6 [110/31] via 10.1.34.4, 00:06:49, FastEthernet0/1

     172.16.0.0/24 is subnetted, 4 subnets

O E2    172.16.4.0 [110/20] via 10.1.34.4, 00:06:49, FastEthernet0/1

O E2    172.16.1.0 [110/20] via 10.1.34.4, 00:06:49, FastEthernet0/1

O E2    172.16.2.0 [110/20] via 10.1.34.4, 00:06:49, FastEthernet0/1

O E2    172.16.3.0 [110/20] via 10.1.34.4, 00:06:50, FastEthernet0/1

     172.25.0.0/24 is subnetted, 4 subnets

O E2    172.25.4.0 [110/20] via 10.1.34.4, 00:06:50, FastEthernet0/1

O E2    172.25.1.0 [110/20] via 10.1.34.4, 00:06:50, FastEthernet0/1

O E2    172.25.3.0 [110/20] via 10.1.34.4, 00:06:50, FastEthernet0/1

O E2    172.25.2.0 [110/20] via 10.1.34.4, 00:06:50, FastEthernet0/1

O IA 192.168.20.0/24 [110/21] via 10.1.23.2, 00:06:50, FastEthernet0/0

     10.0.0.0/24 is subnetted, 5 subnets

O IA    10.1.12.0 [110/20] via 10.1.23.2, 00:06:50, FastEthernet0/0

O IA    10.1.45.0 [110/20] via 10.1.34.4, 00:06:50, FastEthernet0/1

O IA    10.1.56.0 [110/30] via 10.1.34.4, 00:06:50, FastEthernet0/1

O IA routes indicates Inter-area routes which means routes outside R3 area (area 0) and O E2 indicates external routes outside OSPF autonomous system which has been redistributed into it, in this case by R6, using redistribute connected.

In order to optimize and minimize routing table I will use summarization, OSPF supports two type of summarization:

1.       For Inter-area routes which will be performed by the ABR

2.       For external routes which will be performed by the ASBR

So taking the first example, I want to summarize all 192.168.xx.0/24 which advertised by R1, into area 1 and from there advertised to area 0 through R2.

The route summarization will be done on R2 which is the ABR between area 1 and area 0:

R2(config)#router ospf 1

R2(config-router)#area 1 range 192.168.0.0 255.255.192.0

The area x command indicates the area which these routes exists and the summary for these routes which will be advertised by the R2 (the ABR) into all other areas.

The result:

R3#sh ip route ospf

     1.0.0.0/32 is subnetted, 1 subnets

O IA    1.1.1.1 [110/21] via 10.1.23.2, 00:19:14, FastEthernet0/0

     2.0.0.0/32 is subnetted, 1 subnets

O       2.2.2.2 [110/11] via 10.1.23.2, 00:19:14, FastEthernet0/0

     4.0.0.0/32 is subnetted, 1 subnets

O       4.4.4.4 [110/11] via 10.1.34.4, 00:19:14, FastEthernet0/1

     5.0.0.0/32 is subnetted, 1 subnets

O IA    5.5.5.5 [110/21] via 10.1.34.4, 00:19:14, FastEthernet0/1

     6.0.0.0/32 is subnetted, 1 subnets

O IA    6.6.6.6 [110/31] via 10.1.34.4, 00:19:15, FastEthernet0/1

     172.16.0.0/24 is subnetted, 4 subnets

O E2    172.16.4.0 [110/20] via 10.1.34.4, 00:00:33, FastEthernet0/1

O E2    172.16.1.0 [110/20] via 10.1.34.4, 00:00:33, FastEthernet0/1

O E2    172.16.2.0 [110/20] via 10.1.34.4, 00:00:33, FastEthernet0/1

O E2    172.16.3.0 [110/20] via 10.1.34.4, 00:00:33, FastEthernet0/1

     172.25.0.0/24 is subnetted, 4 subnets

O E2    172.25.4.0 [110/20] via 10.1.34.4, 00:00:33, FastEthernet0/1

O E2    172.25.1.0 [110/20] via 10.1.34.4, 00:00:33, FastEthernet0/1

O E2    172.25.3.0 [110/20] via 10.1.34.4, 00:00:33, FastEthernet0/1

O E2    172.25.2.0 [110/20] via 10.1.34.4, 00:00:33, FastEthernet0/1

     10.0.0.0/24 is subnetted, 5 subnets

O IA    10.1.12.0 [110/20] via 10.1.23.2, 00:19:16, FastEthernet0/0

C       10.1.23.0 is directly connected, FastEthernet0/0

O IA    10.1.45.0 [110/20] via 10.1.34.4, 00:19:16, FastEthernet0/1

C       10.1.34.0 is directly connected, FastEthernet0/1

O IA    10.1.56.0 [110/30] via 10.1.34.4, 00:19:16, FastEthernet0/1

O IA 192.168.0.0/18 [110/21] via 10.1.23.2, 00:00:39, FastEthernet0/0

Note that all 192.168.xx.0/24 routes have been gone and only the summary route is in the routing table.

The cost of the summary route is taken from the best cost among the subnets, for example I have configured each of the loopbacks in R1 with different cost:

R1#sh ip ospf interface brief

Interface    PID   Area            IP Address/Mask    Cost  State Nbrs F/C

Lo0          1     1               1.1.1.1/32         1     LOOP  0/0

Fa0/0        1     1               10.1.12.1/24       10    BDR   1/1

Lo4          1     1               192.168.40.1/24    40    P2P   0/0

Lo3          1     1               192.168.30.1/24    30    P2P   0/0

Lo2          1     1               192.168.20.1/24    20    P2P   0/0

Lo1          1     1               192.168.10.1/24    10    P2P   0/0

Now the cost for summary route will be 30, Lo1 cost (which has the best cost among the subnets) + R1 to R2 link cost + R2 to R3 link cost

R3# sh ip route ospf

     1.0.0.0/32 is subnetted, 1 subnets

O IA    1.1.1.1 [110/21] via 10.1.23.2, 02:16:34, FastEthernet0/0

     2.0.0.0/32 is subnetted, 1 subnets

O       2.2.2.2 [110/11] via 10.1.23.2, 02:16:34, FastEthernet0/0

     4.0.0.0/32 is subnetted, 1 subnets

O       4.4.4.4 [110/11] via 10.1.34.4, 02:16:34, FastEthernet0/1

     5.0.0.0/32 is subnetted, 1 subnets

O IA    5.5.5.5 [110/21] via 10.1.34.4, 02:16:34, FastEthernet0/1

     6.0.0.0/32 is subnetted, 1 subnets

O IA    6.6.6.6 [110/31] via 10.1.34.4, 02:16:34, FastEthernet0/1

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

O E2    172.16.4.0/24 [110/20] via 10.1.34.4, 01:57:50, FastEthernet0/1

O E2    172.16.0.0/22 [110/20] via 10.1.34.4, 01:27:32, FastEthernet0/1

     172.25.0.0/21 is subnetted, 1 subnets

O E2    172.25.0.0 [110/20] via 10.1.34.4, 01:44:50, FastEthernet0/1

     10.0.0.0/24 is subnetted, 5 subnets

O IA    10.1.12.0 [110/20] via 10.1.23.2, 02:16:34, FastEthernet0/0

O IA    10.1.45.0 [110/20] via 10.1.34.4, 02:16:34, FastEthernet0/1

O IA    10.1.56.0 [110/30] via 10.1.34.4, 02:16:35, FastEthernet0/1

O IA 192.168.0.0/18 [110/30] via 10.1.23.2, 00:58:38, FastEthernet0/0

Looking in R2 OSPF database reveals the following information:

R2#sh ip ospf database summary 192.168.0.0

            OSPF Router with ID (2.2.2.2) (Process ID 1)

                Summary Net Link States (Area 0)

  LS age: 1796

  Options: (No TOS-capability, DC, Upward)

  LS Type: Summary Links(Network)

  Link State ID: 192.168.0.0 (summary Network Number)

  Advertising Router: R2

  LS Seq Number: 80000005

  Checksum: 0x20D2

  Length: 28

  Network Mask: /18

        TOS: 0  Metric: 20

And

R2#show ip ospf database router internal adv-router 1.1.1.1

            OSPF Router with ID (2.2.2.2) (Process ID 1)

                Router Link States (Area 1)

  Now in min table

  Table index: 26 min 42 sec

  LS age: 218

  Options: (No TOS-capability, DC)

  LS Type: Router Links

  Link State ID: 1.1.1.1

  Advertising Router: R1

  LS Seq Number: 80000014

  Checksum: 0xBF5A

  Length: 96

  Number of Links: 6

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 1.1.1.1

     (Link Data) Network Mask: 255.255.255.255

      Number of TOS metrics: 0

       TOS 0 Metrics: 1

    Link connected to: a Transit Network

     (Link ID) Designated Router address: 10.1.12.2

     (Link Data) Router Interface address: 10.1.12.1

      Number of TOS metrics: 0

       TOS 0 Metrics: 10

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 192.168.40.0

     (Link Data) Network Mask: 255.255.255.0

      Number of TOS metrics: 0

       TOS 0 Metrics: 40

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 192.168.30.0

     (Link Data) Network Mask: 255.255.255.0

      Number of TOS metrics: 0

       TOS 0 Metrics: 30

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 192.168.20.0

     (Link Data) Network Mask: 255.255.255.0

      Number of TOS metrics: 0

       TOS 0 Metrics: 20

         

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 192.168.10.0

     (Link Data) Network Mask: 255.255.255.0

      Number of TOS metrics: 0

       TOS 0 Metrics: 10

Now let’s take the second type and summarize all external routes from R5, which redistribute all 172.25.xx.0/24 using redistribute connected. The route summarization should be occurring on the ASBR which injects the external routes, in this case R5:

R5(config)#router ospf 1

R5(config-router)#summary-address 172.25.0.0 255.255.248.0

The result:

R3#sh ip route

R3# sh ip route ospf

     1.0.0.0/32 is subnetted, 1 subnets

O IA    1.1.1.1 [110/21] via 10.1.23.2, 00:41:29, FastEthernet0/0

     2.0.0.0/32 is subnetted, 1 subnets

O       2.2.2.2 [110/11] via 10.1.23.2, 00:41:29, FastEthernet0/0

     4.0.0.0/32 is subnetted, 1 subnets

O       4.4.4.4 [110/11] via 10.1.34.4, 00:41:29, FastEthernet0/1

     5.0.0.0/32 is subnetted, 1 subnets

O IA    5.5.5.5 [110/21] via 10.1.34.4, 00:41:29, FastEthernet0/1

     6.0.0.0/32 is subnetted, 1 subnets

O IA    6.6.6.6 [110/31] via 10.1.34.4, 00:41:29, FastEthernet0/1

     172.16.0.0/24 is subnetted, 4 subnets

O E2    172.16.4.0 [110/20] via 10.1.34.4, 00:22:46, FastEthernet0/1

O E2    172.16.1.0 [110/20] via 10.1.34.4, 00:22:46, FastEthernet0/1

O E2    172.16.2.0 [110/20] via 10.1.34.4, 00:22:46, FastEthernet0/1

O E2    172.16.3.0 [110/20] via 10.1.34.4, 00:22:46, FastEthernet0/1

     172.25.0.0/21 is subnetted, 1 subnets

O E2    172.25.0.0 [110/20] via 10.1.34.4, 00:09:45, FastEthernet0/1

     10.0.0.0/24 is subnetted, 5 subnets

O IA    10.1.12.0 [110/20] via 10.1.23.2, 00:41:30, FastEthernet0/0

O IA    10.1.45.0 [110/20] via 10.1.34.4, 00:41:30, FastEthernet0/1

O IA    10.1.56.0 [110/30] via 10.1.34.4, 00:41:30, FastEthernet0/1

O IA 192.168.0.0/18 [110/21] via 10.1.23.2, 00:22:52, FastEthernet0/0

Note that for each route summarization the local router, which preform the summarization, install a discard route into his routing table in order to prevent routing loops:

R5#sh ip route ospf

     1.0.0.0/32 is subnetted, 1 subnets

O IA    1.1.1.1 [110/41] via 10.1.45.4, 00:39:32, FastEthernet0/0

     2.0.0.0/32 is subnetted, 1 subnets

O       2.2.2.2 [110/31] via 10.1.45.4, 00:39:32, FastEthernet0/0

     3.0.0.0/32 is subnetted, 1 subnets

O       3.3.3.3 [110/21] via 10.1.45.4, 00:39:32, FastEthernet0/0

     4.0.0.0/32 is subnetted, 1 subnets

O       4.4.4.4 [110/11] via 10.1.45.4, 00:39:32, FastEthernet0/0

     6.0.0.0/32 is subnetted, 1 subnets

O       6.6.6.6 [110/11] via 10.1.56.6, 00:39:53, FastEthernet0/1

     172.16.0.0/24 is subnetted, 4 subnets

O E2    172.16.4.0 [110/20] via 10.1.56.6, 00:20:38, FastEthernet0/1

O E2    172.16.1.0 [110/20] via 10.1.56.6, 00:20:38, FastEthernet0/1

O E2    172.16.2.0 [110/20] via 10.1.56.6, 00:20:38, FastEthernet0/1

O E2    172.16.3.0 [110/20] via 10.1.56.6, 00:20:38, FastEthernet0/1

     172.25.0.0/16 is variably subnetted, 5 subnets, 2 masks

O       172.25.0.0/21 is a summary, 00:07:38, Null0

     10.0.0.0/24 is subnetted, 5 subnets

O IA    10.1.12.0 [110/40] via 10.1.45.4, 00:39:33, FastEthernet0/0

O       10.1.23.0 [110/30] via 10.1.45.4, 00:39:33, FastEthernet0/0

O       10.1.34.0 [110/20] via 10.1.45.4, 00:39:33, FastEthernet0/0

O IA 192.168.0.0/18 [110/41] via 10.1.45.4, 00:20:45, FastEthernet0/0

Now for R6, which also inject connected interfaces (172.16.xx.0/24) using redistribute connected, I will summarize only networks 172.16.1.0/24, 172.16.2.0/24 and 172.16.3.0/24 while leaving 172.16.4.0/24 as it is, but I will add a tag to the summary:

R6(config)#router ospf 1

R6(config-router)#summary-address 172.16.0.0 255.255.252.0 tag 999

The result:

R3# sh ip route ospf           

     1.0.0.0/32 is subnetted, 1 subnets

O IA    1.1.1.1 [110/21] via 10.1.23.2, 00:50:47, FastEthernet0/0

     2.0.0.0/32 is subnetted, 1 subnets

O       2.2.2.2 [110/11] via 10.1.23.2, 00:50:47, FastEthernet0/0

     4.0.0.0/32 is subnetted, 1 subnets

O       4.4.4.4 [110/11] via 10.1.34.4, 00:50:47, FastEthernet0/1

     5.0.0.0/32 is subnetted, 1 subnets

O IA    5.5.5.5 [110/21] via 10.1.34.4, 00:50:47, FastEthernet0/1

     6.0.0.0/32 is subnetted, 1 subnets

O IA    6.6.6.6 [110/31] via 10.1.34.4, 00:50:47, FastEthernet0/1

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

O E2    172.16.4.0/24 [110/20] via 10.1.34.4, 00:32:03, FastEthernet0/1

O E2    172.16.0.0/22 [110/20] via 10.1.34.4, 00:01:45, FastEthernet0/1

     172.25.0.0/21 is subnetted, 1 subnets

O E2    172.25.0.0 [110/20] via 10.1.34.4, 00:19:02, FastEthernet0/1

     10.0.0.0/24 is subnetted, 5 subnets

O IA    10.1.12.0 [110/20] via 10.1.23.2, 00:50:47, FastEthernet0/0

O IA    10.1.45.0 [110/20] via 10.1.34.4, 00:50:47, FastEthernet0/1

O IA    10.1.56.0 [110/30] via 10.1.34.4, 00:50:48, FastEthernet0/1

O IA 192.168.0.0/18 [110/21] via 10.1.23.2, 00:32:09, FastEthernet0/0

Unlike in BGP, in OSPF we can’t advertise the summary route along with original subnet, but in this example I will use tag to decide which router will get the summary and which not. Also remember to we can do route summarization only on contiguous networks only.

Now let’s configure on R4 a filter to deny the summary-route from R6:

R4(config)#route-map RM_FILTER deny 10

R4(config-route-map)#match tag 999 

R4(config)#route-map RM_FILTER permit 20

R4(config)#router ospf 1

R4(config)#distribute-list route-map RM_FILTER in

Now looking on R4 routing table:

R4#sh ip route ospf  

     1.0.0.0/32 is subnetted, 1 subnets

O IA    1.1.1.1 [110/31] via 10.1.34.3, 00:01:30, FastEthernet0/0

     2.0.0.0/32 is subnetted, 1 subnets

O       2.2.2.2 [110/21] via 10.1.34.3, 00:01:30, FastEthernet0/0

     3.0.0.0/32 is subnetted, 1 subnets

O       3.3.3.3 [110/11] via 10.1.34.3, 00:01:30, FastEthernet0/0

     5.0.0.0/32 is subnetted, 1 subnets

O       5.5.5.5 [110/11] via 10.1.45.5, 00:01:30, FastEthernet0/1

     6.0.0.0/32 is subnetted, 1 subnets

O IA    6.6.6.6 [110/21] via 10.1.45.5, 00:01:30, FastEthernet0/1

     172.16.0.0/24 is subnetted, 1 subnets

O E2    172.16.4.0 [110/20] via 10.1.45.5, 00:01:30, FastEthernet0/1

     172.25.0.0/21 is subnetted, 1 subnets

O E2    172.25.0.0 [110/20] via 10.1.45.5, 00:01:30, FastEthernet0/1

     10.0.0.0/24 is subnetted, 5 subnets

O IA    10.1.12.0 [110/30] via 10.1.34.3, 00:01:30, FastEthernet0/0

O       10.1.23.0 [110/20] via 10.1.34.3, 00:01:30, FastEthernet0/0

O IA    10.1.56.0 [110/20] via 10.1.45.5, 00:01:30, FastEthernet0/1

O IA 192.168.0.0/18 [110/40] via 10.1.34.3, 00:01:32, FastEthernet0/0

No summary here only the subnet, looking on R3 routing table:

R3#sh ip route ospf

     1.0.0.0/32 is subnetted, 1 subnets

O IA    1.1.1.1 [110/21] via 10.1.23.2, 18:11:14, FastEthernet0/0

     2.0.0.0/32 is subnetted, 1 subnets

O       2.2.2.2 [110/11] via 10.1.23.2, 18:11:14, FastEthernet0/0

     4.0.0.0/32 is subnetted, 1 subnets

O       4.4.4.4 [110/11] via 10.1.34.4, 18:11:14, FastEthernet0/1

     5.0.0.0/32 is subnetted, 1 subnets

O IA    5.5.5.5 [110/21] via 10.1.34.4, 18:11:14, FastEthernet0/1

     6.0.0.0/32 is subnetted, 1 subnets

O IA    6.6.6.6 [110/31] via 10.1.34.4, 18:11:14, FastEthernet0/1

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks

O E2    172.16.4.0/24 [110/20] via 10.1.34.4, 17:52:31, FastEthernet0/1

O E2    172.16.0.0/22 [110/20] via 10.1.34.4, 00:09:22, FastEthernet0/1

     172.25.0.0/21 is subnetted, 1 subnets

O E2    172.25.0.0 [110/20] via 10.1.34.4, 17:39:30, FastEthernet0/1

     10.0.0.0/24 is subnetted, 5 subnets

O IA    10.1.12.0 [110/20] via 10.1.23.2, 18:11:14, FastEthernet0/0

O IA    10.1.45.0 [110/20] via 10.1.34.4, 18:11:14, FastEthernet0/1

O IA    10.1.56.0 [110/30] via 10.1.34.4, 18:11:16, FastEthernet0/1

O IA 192.168.0.0/18 [110/30] via 10.1.23.2, 16:53:18, FastEthernet0/0

The summary and the subnet are here and can be found on all routers except R4.