A Juniper JNCIA-ER developer is a certified professional who specializes in designing, implementing, and troubleshooting Juniper Networks enterprise routing solutions. They work extensively with Juniper's J-series routers, M-series multiservice edge routers, and E-series broadband services routers. Their tasks include configuring and monitoring routing protocols like OSPF, IS-IS, RIP, and BGP, managing IP addresses, and ensuring network security. They also handle VPNs, MPLS, high availability features, and QoS policies. Their role is crucial in ensuring reliable and efficient network infrastructure for organizations, which enables seamless connectivity and communication.