ipv6 ospf and rip understaning the routing table

hossameldinroshdy

Hello,

I faced an issue that i dont understand the reason for it. A case study to practice the ospf and rip for ipv6 it contains two routers each with one loopback.

when configuring ripng and ospf3 on both routers the loopbacks on both routers are in the routing table with two entries once with ripng (/64) and the other with osps3 (/12. I understand that the two entries must be in the routing table because the different prefix. The question here why rip sends (/64 preifx) while ospf sends (/128 prefix).


R4 table:

R 2011:5555::/64 [120/2]
via FE80::C800:FF:FEDC:8, Serial1/1
O 2011:5555::1/128 [110/64]
via FE80::C800:FF:FEDC:8, Serial1/1


R5 table:
R 2011:1111::/64 [120/2]
via FE80::C803:1CFF:FE48:8, Serial1/1
O 2011:1111::1/128 [110/64]
via FE80::C803:1CFF:FE48:8, Serial1/1

Thanks,
sincerely,
Hossam El-Din Roshdy

lrb

Change the network type to OSPF point-to-point and see what happens Loopbacks in OSPFv2 were included in the router LSAs and advertised as host routes (/32) with the default OSPF network type. In OSPFv3 they are advertised as intra-area-prefix LSAs which you can see as follows:

SW1#show ipv6 ospf database prefix        

            OSPFv3 Router with ID (1.1.1.1) (Process ID 1)

                Intra Area Prefix Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 99
  LS Type: Intra-Area-Prefix-LSA
  Link State ID: 0
  Advertising Router: 1.1.1.1
  LS Seq Number: 80000001
  Checksum: 0x82CF
  Length: 52
  Referenced LSA Type: 2001
  Referenced Link State ID: 0
  Referenced Advertising Router: 1.1.1.1
  Number of Prefixes: 1
  Prefix Address: 2001::1
  [B]Prefix Length: 128[/B], Options: LA, Metric: 0

And as you can see the prefix length is 128 bits, even though the interface address is as follows.

SW1#show run int Lo0
Building configuration...

Current configuration : 106 bytes
!
interface Loopback0
 ip address 1.1.1.1 255.255.255.0
[B] ipv6 address 2001::1/64[/B]
 ipv6 ospf 1 area 0
end

Now we change the OSPF network type to p2p:

SW1(config-if)#ipv6 ospf network point-to-point 

And check the intra-area-prefix LSAs in the LSDB

SW1#show ipv6 ospf database prefix 

            OSPFv3 Router with ID (1.1.1.1) (Process ID 1)

                Intra Area Prefix Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 6
  LS Type: Intra-Area-Prefix-LSA
  Link State ID: 0
  Advertising Router: 1.1.1.1
  LS Seq Number: 80000002
  Checksum: 0x7C1F
  Length: 44
  Referenced LSA Type: 2001
  Referenced Link State ID: 0
  Referenced Advertising Router: 1.1.1.1
  Number of Prefixes: 1
  Prefix Address: 2001::
  [B]Prefix Length: 64[/B], Options: None, Metric: 1

You can check out the OSPFv3 RFC for more info if you are interested. In general they should be configured and advertised as host routes anyway, especially if you don't want LDP (for MPLS) to complain because the MPLS router ID not reachable with a host route

hossameldinroshdy

Thats a hell of an reply its really professional reply. Thanks to you i understand the reason why it was happening. I will try the configuration now. thanks again really appreciate it.