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OSPFv3 Neighbors do not need to be on same subnet

We will use below topology and different subnet at both end, then we will check the adjacency and try to ping in order to confirm.

R2 F0/0 <—–> F0/0 R3

R2 Configuration:

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

R3 Configuration:

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

Checking routes on R2:

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

Trying to ping 2001:3::3 from R2:

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#

Adjacency is establishing and able to ping because neighbors are known by their router-ids. Link-local addresses are used as next-hops, not actual interface address.

Thanks for reading the blog ………..

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