Theory: From the Cisco website: « The OSPF Area Transit Capability feature is enabled by default. RFC 2328 defines OSPF area transit capability as the ability of the area to carry data traffic that neither originates nor terminates in the area itself. This capability enables the OSPF ABR to discover shorter paths through the transit area […]
Read MoreTag: path preference
OSPF – Implement and troubleshoot path preference – Per neighbor cost
Let’s look at another way to influence path preference with OSPF. Theory: Because OSPF cost calculation for a segment is based on the bandwidth value of the outgoing interface, in certain topology, there can be some issues when changing the cost or the bandwidth of the interface. In our topology, if we want […]
Read MoreOSPF – Implement and troubleshoot path preference – Bandwidth
Another way to influence OSPF path selection is to change the bandwidth configured under one interface. Requirements : Ensure that traffic from R4 to R3 loopback goes via R2. Diagram: Configuration and verification: Same as in the previous post, let’s check what’s the current route to R3. R4#sh ip route 33.33.33.33 […]
Read MoreOSPF – Implement and troubleshoot path preference – Cost
Let’s now take a look at how to influence path preference using the cost command. Requirements: Ensure that the traffic from R4 to R3 loopback goes via R2. Diagram: Configuration and verification: At the moment, if we want to reach R3 loopback from R4, the traffic will go through R1. R4#sh […]
Read MoreOSPF – Implement and troubleshoot path preference – Auto cost
Let’s start working on how to influence the OSPF path selection. Theory: The formula for OSPF automatic cost calculation is the following: Interface Cost = Reference Bandwidth / Interface Bandwidth By default, the reference bandwidth is 100Mbps. R1#sh ip ospf | s Reference Reference bandwidth unit is 100 mbps So a 100Mbps […]
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