OSPF LSA-ID Conflict : %OSPF-4-CONFLICTING_LSAID

Today I am going to talk about the OSPF LSA-ID conflict, The OSPF error message showed below as :

OSPF Error Message "%OSPF-4-CONFLICTING_LSAID". LSA origination is prevented by existing LSA with same LSID but a different mask Existing Type 3 LSA: LSID.

Now let's take an example here, If Network 192.168.1.0/24 is redistributed into the OSPF, OSPF process will generates LSA for Network 192.168.1.0/24 using the network-id 192.168.1.0.

Then , when 192.168.1.0/25 is redistributed, the OSPF cannot pick the network-id as the LSA ID because its already being used by 192.168.1.0/24. Hence 192.168.1.0/25 being more specific , it wil Pick the Broadcast address of the network which is 192.168.1.127.

Fig 1.1- OSPF Areas and LSA

Problem Situation:

The OSPF LSA ID Conflicts occurs when OSPF is trying to originate LSA ID for the more specific network (suppose to choose broadcast address)and the LSA ID/Broadcast id is already present in the OSPF topology or
OSPF is trying to generate LSA ID for a host route /32 which is equal to either the Network id or the broadcast of already present LSA ID in the OSPF Topology:

For example:

For Network 192.168.1.2/31, OSPF Assigns LSA-ID as 192.168.1.2, if you try to redistribute a route 192.168.1.2/32 into OSPF, the OSPF fails to generate LSA-ID as the 192.168.1.2 is already present in the OSPF Topology Table.

Hence OSPF generates the Error Message:  "%OSPF-4-CONFLICTING_LSAID: LSA origination prevented by existing LSA with same LSID but a different mask Existing Type 3 LSA: LSID".

Type-5 AS External Link States

Link ID        ADV Router     Age     Seq#          Checksum     Tag

192.168.0.2   1.1.1.1         414   0x80000003      0x00F936      0

OSPF Router with ID (1.1.1.1) (Process ID 10)

Type-5 AS External Link States

 LS age: 453

 Options: (No TOS-capability, DC, Upward)

 LS Type: AS External Link

 Link State ID: 192.168.0.2 (External Network Number )

 Advertising Router: 1.1.1.1

 LS Seq Number: 80000003

 Checksum: 0xF936

 Length: 36

 Network Mask: /31

 Metric Type: 2 (Larger than any link state path)

 MTID: 0 

 Metric: 20 

 Forward Address: 0.0.0.0

 External Route Tag: 0

When you try to redistribute 192.168.0.2/32 into the table, you see:

%OSPF-4-CONFLICTING_LSAID: LSA origination prevented by LSA with same LSID but a different mask

 Existing Type 5 LSA: LSID 192.168.0.2/31

 New Destination: 192.168.0.2/32

Solution

The Solution for the this scenario is careful redistribution of the routes. When redistributing routes( /32 specifically), ensure that it does not conflict with any of the existing LSA ID.