OSPF interfaces have wrong default costs

[IncludeArthur]

Operating system

Ubuntu 20.04

Kathará Version

3.7.7

Lab Name

main-labs/intradomain-routing/frr/ospf

Bug description

In the OSPF labs the interfaces have default cost of 10000 instead of the intended value of 10. This is possibily the result of a wrong configured bandwidth which shows as 10 Mbit instead of 10000 Mbit.

Steps to reproduce

No response

[tcaiazzi]

Dear @IncludeArthur,

Thank you for opening this issue, and apologies for the delayed response.

The behavior you encountered is caused by an unintended side effect of the new network plugin, katharanp_vde. This plugin creates pure L2 LANs using VDE (Virtual Distributed Ethernet) software switches and TAP interfaces. Unfortunately, by default, the Linux operating system assigns a bandwidth of 10 Mbps to TAP interfaces. Since the default cost of an interface is computed based on its bandwidth, this results in an unexpected default cost of 10000.

Fixing the Cost

To resolve this issue, you can manually set the link bandwidth before starting FRR using the ethtool command. For example:

ethtool -s eth0 speed 10000

After this change, starting FRR will give the interface a default cost of 10, as shown here:

Alternatively, you can switch back to the older plugin, katharanp. This plugin is based on Linux bridges, which are assigned a default bandwidth of 10000 Mbps by the operating system. However, please note that the old plugin has its own disadvantages.

Anyway, you’re absolutely right that this behavior should be clarified in the wiki or network plugin documentation. We’ll make sure to address this to avoid future confusion.

Thank you again for bringing this to our attention! Please let me know if this solution works for you, or if there’s anything else I can help with.