BGP Peering: update-source lo with lo having multiple ip addresses. How source-address is decided?

[dyvignaswaroop8]

I'm attempting to comprehend how FRR manages scenarios where "update-source lo" is specified in BGP peering, and the loopback (lo) interface has multiple IP addresses (secondary addresses) configured. In the bgp_update_address() API, it's unclear how the source address is precisely determined in the described situation. Could someone clarify the simplest approach to address this? If a user opts for multiple addresses on the loopback interface and configures "update-source lo" for BGP peering, should we reject the configuration?

[ton31337]

Specify an arbitrary IP instead of the interface name.

[dyvignaswaroop8]

Opting for the address as the source is an alternative choice. However, my focus is on understanding the handling of multiple loopback addresses. How does the FRR determine the source address when configured in this manner?

[donaldsharp]

BGP currently chooses the ip address with the most common bits for the destination it is sending to.