Tracking OSPF LSA

[jagan_240]

Hello Friends ,

I have a requirement to understand the link status (up/Down) between Router C and Router B from Router A through OSPF LSA update via Router B neighbour ID.

From Router A i need to get this information before shutting my Router A to Router C link (1) using automated script.

I have tried with sh ip ospf database adv-router < > , sh ip ospf database router / network < > , but no luck there is no change in LSA .

Can someone share how to achieve the same ?

                    Router A -----( Area 0 )--------- Router B

                                 \                        /

Link 1 ( Area 0 ) ->     \                     /   <-- Link 2 ( Area 0 )

                                       Router C

Thanks

[Akash Agrawal]

Hi,

A router advertises link state information, for all its ospf enabled interfaces, via router LSA (LSA type-1) or network LSA (LSA type-2) based on you are using network point-to-point or broadcast.

In below example i am using network point-to-point in all links

Topology:

R1----R3----R4

R1-R3 link ip add : 172.31.13.x

R3-R4 link ip add : 172.31.34.x

Loopback ips x.x.x.x

x is router number.

In below router LSA R3 is informing R4 about its Loopback ip, link status and ip subnet details for link connected to R1 and same for link connected to R4

R4#show ip ospf database router 3.3.3.3

            OSPF Router with ID (4.4.4.4) (Process ID 100)

                Router Link States (Area 0)

  LS age: 41
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 3.3.3.3
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000006
  Checksum: 0xE212
  Length: 72
  Number of Links: 4

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 3.3.3.3  <<<<<<<<< Loopback0
     (Link Data) Network Mask: 255.255.255.255
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 172.31.13.0 <<<<<<<< Link connected to R1
     (Link Data) Network Mask: 255.255.255.0
      Number of MTID metrics: 0
       TOS 0 Metrics: 10

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 4.4.4.4
     (Link Data) Router Interface address: 172.31.34.3
      Number of MTID metrics: 0
       TOS 0 Metrics: 10

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 172.31.34.0  <<<<<<< Link connected to R4
     (Link Data) Network Mask: 255.255.255.0
      Number of MTID metrics: 0
       TOS 0 Metrics: 10

If i shut R1-R3 link, R3 will send updated router LSA to R4. You can observe the difference in two output.

R4#show ip ospf database router 3.3.3.3

            OSPF Router with ID (4.4.4.4) (Process ID 100)

                Router Link States (Area 0)

  LS age: 16
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 3.3.3.3
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000012
  Checksum: 0x8853
  Length: 60
  Number of Links: 3

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 3.3.3.3
     (Link Data) Network Mask: 255.255.255.255
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 4.4.4.4
     (Link Data) Router Interface address: 172.31.34.3
      Number of MTID metrics: 0
       TOS 0 Metrics: 10

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 172.31.34.0
     (Link Data) Network Mask: 255.255.255.0
      Number of MTID metrics: 0
       TOS 0 Metrics: 10

R4#

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Regards,

Akash