OSPF route calculation in Cisco 1841 IOS 12.4

[sina.naser]

Hi Everyone,

We have a WAN topology with thousands branches and one DC and one DR. We change OSPF metric types to E1 so We can See DC networks from DC tunnel and DR network from DR Tunnel. This worked on IOS 15 Routers But in IOS 12 after even clear OPSF process all network always prefereed from one tunnel But the metrics is correct!!!!!

I appreciate any help

Tnx in advance

[Joseph W. Doherty]

Could your OSPF metric exceed 64K?

I recall (??) later IOS's OSPF support metrics using more than 2 bytes.

Just tried to find confirming documentation, no success.

[Joseph W. Doherty]

Still have not found documentation.

Also recall (??) it was also related to externals.  In that they had a larger metric field.(??). If so, possiblity ver. 15 handles better/correctly vs. ver. 12.

The person most likely to know, might be @Peter Paulik 

[sina.naser]

ip ospf databse external command show the correct metric BTW in IOS 12.4. But show ip route is incorrect and shows the worst metric

[Joseph W. Doherty]

Is the correct external metric greater than 64K?

[sina.naser]

No teir metric are 28 and 26 respectively via "ip ospf databse external" command

[Joseph W. Doherty]

Do you have a representative example, you can post, of the discrepancy between vers. 12 and 15, for any route, using the show OSPF and route commands?

If not between vers. 12 and 15, between those commands show the metric differences for just version 12?

[sina.naser]

The metrics are correct and same in both version in OSPF database. The problem is in IOS 12.4 the best (lowest) metric didn't install in Routing table.

[Joseph W. Doherty]

Well in that case, sounds like a software defect.

Years ago, in one of the earlier release trains of 12.x, I found, then, an unknown bug in OSPF.  Reported it.  A couple of releases later, Cisco fixed it.

Your simple choices might be:  use 15.x or, if that 12.4 is still supported, and you have maintenance, open a TAC case.

[Joseph W. Doherty]

Ah, did find some LSAs only have a 2 byte metric and some (like externals) have a 3 byte metric.  (Finding this [again] refreshes my memory - I was working an OSPF case where metric exceeded 64K, which surprised me, but it was an external.  So, if you're exceeding 64K metrics, wouldn't surprise me vers. 12 and 15 don't work the same.)

[sina.naser]

All of the metrics are below 30 

[MHM Cisco World]

The ospf ver. Different between two routers'

Can you check which ospf ver. You run in both ?

[sina.naser]

OSPF version are same. OSPF PID and area are also same.

[MHM Cisco World]

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/117824-config-ospf-00.html

Not ospfv2 or opsfv3 what I talk' ospf have many rfc and each one have different behave for opsf path select.

I think two routers use different ospf rfc ver.

[sina.naser]

How can I verify OSPF rfc via show commands?