BGP is a path-vector routing protocol, every router on the internet is constantly updating its routing tables based on paths provided by its peers to get the shortest distance to an advertised prefix. When a new route is announced it takes time to propagate through the network and for all routers in the chain to “converge” into a single coherent view.
If this is indeed a reconvergence event, that would imply there’s been a cascade of route table updates that have been making their way through CTL/L3’s network - meaning many routers are missing the “correct” paths to prefixes and traffic is not going where it is supposed to, either getting stuck in a routing loop or just going to /dev/null because the next hop isn’t available.
This wouldn’t be such a huge issue if downstream systems could shut down their BGP sessions with CTL and have traffic come in via other routes, but doing so is not resulting in the announcements being pulled from the Level 3 AS - something usually reflective of the CPU on the routers being overloaded processing route table updates or an issue with the BGP communication between them.
If this is indeed a reconvergence event, that would imply there’s been a cascade of route table updates that have been making their way through CTL/L3’s network - meaning many routers are missing the “correct” paths to prefixes and traffic is not going where it is supposed to, either getting stuck in a routing loop or just going to /dev/null because the next hop isn’t available.
This wouldn’t be such a huge issue if downstream systems could shut down their BGP sessions with CTL and have traffic come in via other routes, but doing so is not resulting in the announcements being pulled from the Level 3 AS - something usually reflective of the CPU on the routers being overloaded processing route table updates or an issue with the BGP communication between them.
Convergence time is a known bugbear of BGP.