cr1-codfw and cr2-codfw connect to each other via an aggregate of two 10G links, but each router has only one FPC linecard, and said linecard has both the cross-router links, as well as the peering/transit links, and the cross-cluster transport links.

This means that, if the FPC linecard fails on the current VRRP master, all codfw hosts will lose connectivity to the outside world indefinitely, until someone intervenes.

Possible solutions include adding a special router-to-router vlan to the row switches, or just buying more linecards and using them for the router-to-router link.

Incident: https://wikitech.wikimedia.org/wiki/Incidents/2020-03-25_codfw-network