Why p2p link is showing as transit network

[veerendrav2]

Why Type-2 LSA are propagated in between R1 and R5(Area 1)? here is my configuration

R1#show ip ospf database 

            OSPF Router with ID (192.168.10.1) (Process ID 1)

		Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
192.168.10.1    192.168.10.1    274         0x80000002 0x00DA78 1
192.168.10.2    192.168.10.2    276         0x80000002 0x00D57B 1
192.168.10.3    192.168.10.3    275         0x80000003 0x00D477 1
192.168.10.4    192.168.10.4    275         0x80000002 0x009C6B 2

		Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
192.168.10.4    192.168.10.4    275         0x80000001 0x00FF6B

		Summary Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
10.10.1.0       192.168.10.1    310         0x80000001 0x008F1A
10.20.1.0       192.168.10.3    303         0x80000002 0x000993

		Router Link States (Area 1)
          
Link ID         ADV Router      Age         Seq#       Checksum Link count
10.10.1.2       10.10.1.2       256         0x80000002 0x006E5F 1
192.168.10.1    192.168.10.1    257         0x80000002 0x00B85A 1
          
                Net Link States (Area 1)
          
Link ID         ADV Router      Age         Seq#       Checksum
10.10.1.1       192.168.10.1    260         0x80000001 0x0036ED
          
                Summary Net Link States (Area 1)
          
Link ID         ADV Router      Age         Seq#       Checksum
10.20.1.0       192.168.10.1    324         0x80000001 0x007B1A
10.30.1.0       192.168.10.1    326         0x80000001 0x000388
192.168.10.0    192.168.10.1    367         0x80000001 0x0075D5

At R5,

R5#show ip ospf database router 192.168.10.1

            OSPF Router with ID (10.10.1.2) (Process ID 1)

		Router Link States (Area 1)

  Routing Bit Set on this LSA
  LS age: 1232
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 192.168.10.1
  Advertising Router: 192.168.10.1
  LS Seq Number: 80000002
  Checksum: 0xB85A
  Length: 36
  Area Border Router
  Number of Links: 1

    Link connected to: a Transit Network
     (Link ID) Designated Router address: 10.10.1.1
     (Link Data) Router Interface address: 10.10.1.1
      Number of TOS metrics: 0
       TOS 0 Metrics: 10

You can see in above show command, the R1 router is connected to Transit Network. It is p2p link, isn't it?

And there is a DR in Area 1?

R5#show ip ospf neighbor 

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.10.1      1   FULL/DR         00:00:31    10.10.1.1       FastEthernet0/1

Or should configure those links as p2p explicitly?

[Meheretab Mengistu · Accepted solution]

Hi,

In OSPF, Ethernet links are treated as Broadcast network type even if they physical connection is point-to-point. 

Why Type-2 LSA are propagated in between R1 and R5(Area 1)?

Since the connection between R1 and R5 is using Ethernet link (where the default network type is Broadcast), you will have DR/BDR election and also Type-2 LSA.

You can see in above show command, the R1 router is connected to Transit Network. It is p2p link, isn't it? And there is a DR in Area 1? Or should configure those links as p2p explicitly?

Yes, you will need to change your network type to "point-to-point" if you do not want to have Type-2 LSA, and no DR/BDR election. The command is:

int fa0/1

 ip ospf network point-to-point

!

Check the change by running "sh ip ospf interface fa0/1".

HTH,

Meheretab

[Julio E. Moisa]

Hi,

The transit networks represents the networks with the capabilities to transport traffic that is not locally generated or locally destined. Router LSA considered the local connected subnets as stub type. 

This link could be useful:

http://thenetworksherpa.com/ospf-making-sense-of-router-lsa-point-to-point-links/

:-)

[paul driver]

Hello

Please review this excellant post by the Mr Peter Paulch - Very definative answer to your query. - Here
It will explain in much more detail then I ever could thats for sure!

res
Paul