This paper proposes an isolation layer -- a shim -- betweeninter-domain routing and packet forwarding. The job of this layer isto coordinate between Autonomous Systems (AS's) on when and how tomodify the forwarding state to ensure inter-domain routing loops donot cause forwarding loops. The benefits of a consistency layer aretwofold. First, it prevents the creation of transient inter-domainforwarding loops and the resulting packet loss, high latency, andconnection failures.Second, by taking the burden of forwarding consistency off theinter-domain routing protocol, it enables inter-domain routingprotocols with more complex convergence characteristics than BGP, suchas protocols that optimize route selection based on performance. Weoffer two possible designs for the consistency layer. We prove thatboth designs are free of forwarding loops and show they are easy todeploy in the current Internet.