OSPFv3 Summarization

This lesson continues from the multi-area topology built in OSPFv3 Configuration: R1 and R2 in Area 0, R2 and R3 in Area 1, all adjacencies FULL.

Figure 1 - OSPFv3 multi-area topology

The last feature you need to understand is IPv6 route summarization in OSPFv3.

Figure 2 - OSPFv3 IPv6 Summarization

In this example, you will summarize four networks into a single summary route using the ABR.

Step 1 – Create Loopback Prefixes

First, create four loopback interfaces on R1.
Each loopback represents a different IPv6 network inside Area 0.

On R1:

R1# conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)# int lo0
R1(config-if)# ipv6 address 2001:db8:100:0::1/64
R1(config-if)# ospfv3 1 ipv6 area 0
R1(config-if)# exit

R1(config)# int lo1
R1(config-if)# ipv6 address 2001:db8:100:1::1/64
R1(config-if)# ospfv3 1 ipv6 area 0
R1(config-if)# exit

R1(config)# int lo2
R1(config-if)# ipv6 address 2001:db8:100:2::1/64
R1(config-if)# ospfv3 1 ipv6 area 0
R1(config-if)# exit

R1(config)# int lo3
R1(config-if)# ipv6 address 2001:db8:100:3::1/64
R1(config-if)# ospfv3 1 ipv6 area 0
R1(config-if)# end

You now have four distinct /64 networks in Area 0:

• 2001:db8:100:0::/64

• 2001:db8:100:1::/64

• 2001:db8:100:2::/64

• 2001:db8:100:3::/64

Step 2 – Configure Summarization on the ABR

Summarization in OSPF must be configured on the ABR.

• R2 is the ABR between Area 0 and Area 1.

Using subnetting logic, you can summarize the four /64 networks into: 2001:db8:100:0::/62
Now configure it on R2:

R2# conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)# router ospfv3 1
R2(config-router)# address-family ipv6 unicast
R2(config-router-af)# area 0 range 2001:db8:100:0::/62

This command tells the ABR:

• Summarize the networks in Area 0 that match this prefix.

• Advertise them as a single /62 prefix into other areas.

Step 3 – Verify Summarization

Now verify the result on R3 (Area 1):

R3# show ipv6 route ospf 
IPv6 Routing Table - default - 6 entries
Codes: RL - RPL, O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1

OI  2001:DB8:10::/64 [110/3]
     via FE80::52F7:B4FF:FE00:1301, GigabitEthernet0/0
OI  2001:DB8:11::/64 [110/2]
     via FE80::52F7:B4FF:FE00:1301, GigabitEthernet0/0
OI  2001:DB8:100::/62 [110/2]
     via FE80::52F7:B4FF:FE00:1301, GigabitEthernet0/0

Instead of seeing four separate /64 routes, you now see:

• A single summarized route

• Marked as OI (Inter-Area)

• Learned from the ABR (R2)