OSPFv3 Neighbors do not need to be on same subnet

Check it out:

R2 F0/0 <-----> F0/0 R3

Here is R2's config:

R2#sho run int f0/0
Building configuration...

Current configuration : 153 bytes
!
interface FastEthernet0/0
 no ip address
 duplex auto
 speed auto
 ipv6 address 2001:2::2/64
 ipv6 address FE80::2 link-local
 ipv6 ospf 1 area 0
end

Here is R3's config:

R3#sho run int f0/0
Building configuration...

Current configuration : 153 bytes
!
interface FastEthernet0/0
 no ip address
 duplex auto
 speed auto
 ipv6 address 2001:3::3/64
 ipv6 address FE80::3 link-local
 ipv6 ospf 1 area 0
end

R2's show commands:

R2#sho ipv6 ospf ne   

Neighbor ID     Pri   State           Dead Time   Interface ID    Interface
3.3.3.3           1   FULL/DR         00:00:35    4               FastEthernet0/0

R2#sho ipv6 route  
IPv6 Routing Table - 5 entries
Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP
       U - Per-user Static route
       I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary
       O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
       ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
C   2001:2::/64 [0/0]
     via ::, FastEthernet0/0
L   2001:2::2/128 [0/0]
     via ::, FastEthernet0/0
O   2001:3::/64 [110/10]
     via ::, FastEthernet0/0
L   FE80::/10 [0/0]
     via ::, Null0
L   FF00::/8 [0/0]
     via ::, Null0

R2 can now ping 2001:3::3

R2#ping 2001:3::3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:3::3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/20/56 ms
R2#

This is possible because neighbors are known by their router-ids and link-local addresses are used as next hops, not the actual interface addresses.

IPv6: Summarizing OSPFv3 addresses

This is from IPexpert volume 1 section 22. We have to summarize the following routes:

2020:100:100:2222::/64
2020:100:100:2666::/64

This is how I do it:

1) Identify the hextet ( I don't know if this is a word, I derived it from octet) where we will summarize. This is the 4th hextet. So we know our subnet will be somewhere between /48 and /64.

2) Break it down in binary:

2222 = 0010 0010 0010 0010
2666 = 0010 0110 0110 0110

Converting hex to binary is easy because we just treat each digit in the IPv6 address as a 4 bit binary number by itself. Notice how all the 2's broke down to 0010.

3) Find the common bits. I highlighted them in red below. We have 5 of them. We will use to get our mask.

2222 = 0010 0010 0010 0010
2666 = 0010 0110 0110 0110

4) Set the rest if the bits to 0 and calculate the summary, convert to hex.

summary = 0010 0000 0000 0000 = 2000

5) Calculate subnet mask by adding the common bits to the lower of our subnet range. This means we add 5 to /48 which makes /53.

So our summary address is 2020:100:100:2000::/53

In OSPFv3 we would enter:

R2(config)#ipv6 router ospf 1
R2(config-rtr)#area 1 range 2020:100:100:2000::/53

Check our other routers for the summary:

R4#show ipv6 route | inc 53
OI 2020:100:100:2000::/53 [110/129]