Networking

OSPFv3 Neighbors do not need to be on same subnet

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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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