OSPF - LSA Aged to MaxAge

[Paulo Moreira Magalhaes]

Hello guys

I'm facing a problem with LSAs MaxAge log messages. There is no links up/down, interface congestion and no comunications problems. So I have a lot o log messages as follow:

Summary: LSA Aged to MaxAge ( Area: 0.0.0.0, Type: Summary Link, LSID: 10.210.72.0, Router: 10.212.217.251 )
AlertKey:ospfLsdbEntry.0.0.0.0.3.10.210.72.0.10.212.217.251
Summary: LSA Aged to MaxAge ( Area: 0.0.0.0, Type: AS External Link, LSID: 10.212.164.0, Router: 10.212.217.251 )
AlertKey:ospfLsdbEntry.0.0.0.0.5.10.212.164.0.10.212.217.251

P.S.: all neighbors are members of the same VRF, and ospf is redistributing some networks of others ospf processes.

I'll so tankful if someone can help me.

Paulo Magalhães

[Mahesh Gohil · Accepted solution]

Hello Paulo,

Just giving some bried for ospf maxage. There are two cases when lsa reach maxage

1- When sequence number reaches to its max value.

   OSPF uses a 32-bit signed, linear sequence number space  ranging from InitialSequenceNumber (0x80000001) to MaxSequenceNumber (0x7fffffff). When a router originates an LSA, the router sets the LSA's sequence number to InitialSequenceNumber. Each time the router produces a new instance of the LSA, the router increments the sequence number by one.

     If the present sequence number is MaxSequenceNumber and a new instance of the LSA must be created, the router must first flush the old LSA from all databases. This is done by setting the age of the existing LSA to MaxAge and reflooding it over all adjacencies. As soon as all adjacent neighbors have acknowledged the prematurely aged LSA, the new instance of the LSA with a sequence number of InitialSequenceNumber may be flooded.

   When an LSA reaches MaxAge, the LSA is reflooded and then flushed from the database. When a router needs to flush an LSA from all databases, it prematurely sets the age to MaxAge and refloods it. Only the router that originated the LSA can prematurely age it.

2- When maxage timer reached

   If they reach MaxAge (1 hour), they are flushed from the OSPF domain. The implication here is that there must be a mechanism for preventing legitimate LSAs from reaching MaxAge and being flushed. This mechanism is the link-state refresh. Every 30 minutes, known as the LSRefreshTime, the router that originated the LSA floods a new copy of the LSA with an incremented sequence number and an age of zero. Upon receipt, the other OSPF routers replace the old copy of the LSA and begin aging the new copy.

Can you check does any of the above case hapens to your network

Regards

Mahesh

[Nagendra Kumar Nainar · Accepted solution]

Hi Paulo,

Am I assuming right that this is Type 3 LSA?. If yes, Check if the ABR (which originates this Type3) is getting this prefix removed from DB. Basically when any internal router sends Type1 or Type2 LSA with link removed, ABR will send Type3 LSA to other areas with same seq no but max age set.

This may not be due to link flap on this router but the could be due to flap on the router where this prefix is connected.

HTH,
Nagendra

[Paulo Moreira Magalhaes]

Hello Everybody,

I'm so thankful with your help.

The ASBR routers are flushing and flooding LSA when MaxAge expires or some links goes down, as Mahesh and Nagendra have sad.

The snmp sever get this traps by the OID ospfLsdbEntry, wich is provided by the following configuration:

snmp-server enable traps ospf lsa
snmp-server enable traps ospf cisco-specific lsa

So, we conclude that this a normal condition.