Higher cost OSPF path over normal area is preferred over lower cost path in backbone area.

Higher cost OSPF path over normal area is preferred over lower cost path in backbone area.

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Created On 11/13/19 04:17 AM - Last Modified 07/29/21 23:20 PM


Symptom


  • OSPF configured  on the Firewall similar to the network diagram.
  • Network 172.16.10.0/24 is redistributed into OSPF as Type 1 External.
  • Cost of the route through Area 1 is higher than Area 0.
  • Firewall prefers Area1 path with higher cost than the lower cost Backbone Area 0 Path.
Network Diagram

Environment


  • PAN-OS 7.1 and above.
  • Palo Alto Firewall.
  • OSPF with multiple areas and redistribution.

Cause


Intra-area non Backbone area paths are preferred over Intra-area Backbone aea Paths. This is as per RFC 2328.

 

Resolution


Enable RFC 1583 Compatibility using GUI: Network > Virtual Routers > (select the VR) >; OSPF > Advanced > Check on RFC 1583 Compatibility.
Enabling this causes the path selection based solely on cost. So the lower cost OSPF route via backbone area is preferred over the second normal area path.
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