Internet connectivity is changing. Autonomous Systems (ASes) can now reach hundreds of networks directly through Internet eXchange Points (IXPs). Despite the benefits, any pair of ASes needs first to agree on exchanging traffic. By surveying 100+ network operators, we discovered that this process is mainly manual and lengthy. Because of the hassle, ASes miss interconnection opportunities and prefer long-term agreements, even if not matching current Internet traffic dynamics. To facilitate establishing agreements in short time frames, we propose Dynam-IX, a framework that arms operators with two components: a high-level interconnection intent abstraction, which allows them to express their interconnection policies, and a protocol to automate discovering and offering interconnection opportunities. Dynam-IX provides a trustworthy environment where networks agree to interconnect without relying on any central entity. To realize this, we use a blockchain infrastructure to allow operators to query for interconnection proposals and securely store agreement records. We evaluate a prototype built atop Hyperledger Fabric and show that an AS can establish tens of agreements within a minute, unleashing possibilities for traffic engineering, increasing link utilization and creating economic opportunities. Our proposal has already spurred interest for deployment at an international service provider and a large IXP.