From: Geert Nijs (geert.nijs@simac.be)
Date: Mon Aug 27 2007 - 06:40:01 ART
Hi all,
Last day, i came across a very strange situation.
I have two routers in OSPF area 0, injecting the same routes with a different metric.
When i shutdown the connection to the primary router (OSPF neighbor is gone), my routing table changes towards the secundary router, as expected.
I would expect that the route prefixes in the OSPF database would also be erased, however, the previously best route LSA stays in my OSPF database as can be seen below.
Even resetting the OSPF process did not help (clear ip ospf process) ! After the router resynchronised with the others, it came back.
The LSA is still in my database, and it has a better metric, however it is not "selected" in the routing table. The only difference is that at this time - when
the connection is shut - the "Routing Bit Set" is removed from the LSA. When the connection is enabled, the "Routing Bit" is enabled again on the LSA.
What is the goal of this "Routing Bit" ? Is it to select "valid" LSAs ?
I must say that i have enabled iSPF. Is this part of the iSPF behaviour maybe ?
router ospf 1
ispf
<output removed>
sh ip ospf data external 10.65.0.40
OSPF Router with ID (10.56.157.11) (Process ID 1)
Type-5 AS External Link States
Routing Bit Set on this LSA <<<<<<<<<<<--- "Routing Bit Set"
LS age: 1782 <<<<<<<--- This LSA is currently selected in the routing table
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 10.65.0.40 (External Network Number )
Advertising Router: 199.161.143.238
LS Seq Number: 800000FC
Checksum: 0x60A9
Length: 36
Network Mask: /30
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 65 <<<<<<<<<<--------- worst metric
Forward Address: 0.0.0.0
External Route Tag: 65301 <<<<<<<<<<---------- backup path
LS age: 1831
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 10.65.0.40 (External Network Number )
Advertising Router: 199.161.157.121 <<<<<<<<<-- the link to this router has been SHUTDOWN, however the LSA is still in my database.
LS Seq Number: 800000B3 <<<<<<<<--- LSA is missing the "Routing Bit Set"
Checksum: 0x5F8F
Length: 36
Network Mask: /30
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 10 <<<<<<<<<<----- the best metric
Forward Address: 0.0.0.0
External Route Tag: 65304 <---------------- this is the primary path
regards,
Geert
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