OSPF: Understanding Topology and Troubleshooting


 

 

AGENDA’S

TOPOLOGY FORMATION

TROUBLESHOOTING

 

 

TOPOLOGY FORMATION

 

How to check interfaces on which OSPF is enabled?

Details: Here, output will include all the physical and Virtual interfaces on which OSPF is enabled
Router#sh ip ospf int brInterface PID Area IP Address/Mask Cost State Nbrs F/C

Lo0 100 0 10.144.1.4/32 1 LOOP 0/0

Gi1/2 100 0 10.144.1.13/30 1 DR 1/1

Gi2/2 100 0 10.144.1.9/30 1 BDR 1/1

Vl696 100 0 10.144.1.185/29 1 BDR 1/1

Vl2 100 0 10.144.2.8/24 1 DOWN 0/0

Vl90 100 0 10.144.90.1/27 1 DOWN 0/0

Gi1/1 100 0 10.146.1.7/28 2 DROTH 2/7

 

 

How to check network type configured for every OSPF enabled interface?

How to check RID on OSPF enabled router?

How to check Hello and dead timer?

Details: For interface Gi1/2, Network type is Broadcast. In Broadcast type network, DR and BDR is selected, others are in DROTHER state. Here DR and its own RID are same. So, This router is acting as DR in Broadcast network. Hello and Dead timer values are 10 and 40, Router ID is 10.144.1.4
Router#sh ip ospf intGigabitEthernet1/2 is up, line protocol is up (connected)

Internet Address 10.144.1.13/30, Area 0

Process ID 100, Router ID 10.144.1.4, Network Type BROADCAST, Cost: 1

Transmit Delay is 1 sec, State DR, Priority 1

Designated Router (ID) 10.144.1.4, Interface address 10.144.1.13

Backup Designated router (ID) 10.144.1.3, Interface address 10.144.1.14

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

 

 

How to check LSA types?

Details: All LSA types are mentioned below along with output database.In LSA-1 database, link count presents total number of OSPF enabled interfaces on a particular router
4507-MPLS#sh ip ospf databaseOSPF Router with ID (10.144.1.4) (Process ID 100)

 

Router Link States (Area 0)       à  LSA-1

Link ID             ADV Router        Age         Seq#                  Checksum Link count

10.144.1.3      10.144.1.3          386         0x80028B40     0x009926  50

10.144.1.4      10.144.1.4          483         0x8000C4C4     0x00F601  5

10.144.1.190  10.144.1.190    1019        0x8000A725     0x008477 1

 

Net Link States (Area 0)          -à LSA-2

Link ID         ADV Router            Age         Seq#                   Checksum

10.144.1.10     10.146.1.222    257         0x80007BF7 0x005834

10.144.1.13     10.144.1.4      1768        0x8000C3DF 0x0018FB

10.144.1.162    10.144.1.3      1201        0x8000C3D4 0x005859

 

Summary Net Link States (Area 0)    àLSA-3

Link ID                ADV Router      Age         Seq#       Checksum

10.159.1.144    10.159.1.153    625         0x8000A0F3 0x00FA35

10.159.9.104    10.159.9.113    12          0x80003044 0x009DF2

 

Summary ASB Link States (Area 0)    àLSA-4

Link ID                ADV Router      Age         Seq#       Checksum

213.12.66.75    10.159.1.153    625         0x80007231 0x009F45

213.12.66.76    10.159.9.113    12          0x80001771 0x00DF3F

 

Type-5 AS External Link States        àLSA-5

Link ID         ADV Router      Age         Seq#       Checksum Tag

0.0.0.0         10.144.1.3      1242        0x800091D9 0x006CE5 65225

0.0.0.0         10.146.1.222    365         0x800091DB 0x003141 65225

 

 

How to check all borders routers in a network?

Details: Output will show all the border routers, including ABR and ASBR, present in all the areas of network
4507-MPLS#sh ip ospf border-routersOSPF Process 100 internal Routing TableCodes: i – Intra-area route, I – Inter-area route

i 10.146.192.142 [3] via 10.146.1.6, GigabitEthernet1/1, ASBR, Area 0, SPF 13514

I 213.12.66.75 [13] via 10.144.1.10, GigabitEthernet2/2, ASBR, Area 0, SPF 13514

I 213.12.66.75 [13] via 10.144.1.14, GigabitEthernet1/2, ASBR, Area 0, SPF 13514

I 213.12.66.76 [14] via 10.146.1.3, GigabitEthernet1/1, ASBR, Area 0, SPF 13514

i 10.144.99.4 [2] via 10.144.1.14, GigabitEthernet1/2, ABR/ASBR, Area 0, SPF 13514

i 10.144.99.4 [2] via 10.144.1.10, GigabitEthernet2/2, ABR/ASBR, Area 0, SPF 13514

 

 

TROUBLESHOOTING

 

 

How to check network type configured for every OSPF enabled interface?

How to check RID on OSPF enabled router?

How to check Hello and dead timer?

Details: For interface Gi1/2, Network type is Broadcast. In Broadcast type network, DR and BDR is selected, others are in DROTHER state. Here DR and its own RID are same. So, This router is acting as DR in Broadcast networkHello and Dead timer values are 10 and 40, Router ID is 10.144.1.4
Router#sh ip ospf intGigabitEthernet1/2 is up, line protocol is up (connected)

Internet Address 10.144.1.13/30, Area 0

Process ID 100, Router ID 10.144.1.4, Network Type BROADCAST, Cost: 1

Transmit Delay is 1 sec, State DR, Priority 1

Designated Router (ID) 10.144.1.4, Interface address 10.144.1.13

Backup Designated router (ID) 10.144.1.3, Interface address 10.144.1.14

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

 

 

How to check OSPF traffic?

Details: Here, output will show stats like different type of packets transferring for every individual interface. It is showing all the error types also.
4507-MPLS#sh ip ospf trafficInterface statistics:Interface Loopback0

OSPF packets received/sent

Invalid Hellos DB-des LS-req LS-upd LS-ack Total

Rx: 0 0 0 0 0 0 0

Tx: 0 0 0 0 0 0 0

OSPF header errors

Length 0, Auth Type 0, Checksum 0, Version 0,

Bad Source 0, No Virtual Link 0, Area Mismatch 0,

No Sham Link 0, Self Originated 0, Duplicate ID 0,

Hello 0, MTU Mismatch 0, Nbr Ignored 0,

LLS 0, Unknown Neighbor 0, Authentication 0,

TTL Check Fail 0,

OSPF LSA errors

Type 0, Length 0, Data 0, Checksum 0,

 

 

How to check total number of active interfaces on router for which OSPF is enabled?

How to check to which area type every OSPF enabled interface is connected?

Details: Login to any device in the OSPF network. You can check above mentioned details for any of the OSPF enabled router in the network. Simply, put the RID of the required router at the last in the command
4507-MPLS#sh ip ospf database router 10.144.1.4OSPF Router with ID (10.144.1.4) (Process ID 100)

Router Link States (Area 0)

 

  LS age: 1940

  Options: (No TOS-capability, DC)

  LS Type: Router Links

  Link State ID: 10.144.1.4

  Advertising Router: 10.144.1.4

  LS Seq Number: 8000C4C3

  Checksum: 0xF8FF

  Length: 84

  Number of Links: 5

 

    Link connected to: a Stub Network

     (Link ID) Network/subnet number: 10.144.1.4

     (Link Data) Network Mask: 255.255.255.255

      Number of TOS metrics: 0

       TOS 0 Metrics: 1

 

    Link connected to: a Transit Network

     (Link ID) Designated Router address: 10.144.1.13

     (Link Data) Router Interface address: 10.144.1.13

      Number of TOS metrics: 0

       TOS 0 Metrics: 1

 

    Link connected to: a Transit Network

     (Link ID) Designated Router address: 10.144.1.10

     (Link Data) Router Interface address: 10.144.1.9

      Number of TOS metrics: 0

       TOS 0 Metrics: 1

 

    Link connected to: a Transit Network

     (Link ID) Designated Router address: 10.144.1.190

     (Link Data) Router Interface address: 10.144.1.185

      Number of TOS metrics: 0

       TOS 0 Metrics: 1

 

    Link connected to: a Transit Network

     (Link ID) Designated Router address: 10.146.1.4

     (Link Data) Router Interface address: 10.146.1.7

      Number of TOS metrics: 0

       TOS 0 Metrics: 2

 

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One comment

  1. OSPF, this always haunts me
    Good to see detailed info for understanding topology & to troubleshoot issues
    Specially, details given with command output .. Nice Job done 🙂

    Like

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