This led to IP connectivity issues for both inbound and outbound calls via our network from 11:03 - 11:11 and 14:11 - 15:33, which would have affected both existing calls and new call setups. Here is a summary of our ISP's response, and the steps taken to resolve the issue:
"At 11:04, CenturyLink identified an issue to be affecting users across multiple markets. The IP NOC was engaged, and initial research identified that an offending flowspec announcement prevented BGP from establishing across multiple elements throughout the CenturyLink network. The IP NOC deployed a global configuration change to block the offending flowspec announcement, which allowed BGP to begin to correctly establish."