This chapter describes the LISP core architecture and components. As discussed in this chapter, various LISP nodes play important roles in LISP. This chapter discusses details of the roles and functionality of xTRs, PxTRs, MR/MS, and ALT. This chapter also describes the various packet formats in exchanging LISP control plane messages. It is important to understand the purpose of various LISP control plane messages and when and from where they are triggered. This chapter also covers how to scale a LISP deployment for the global Internet by using LISP-DDT. The chapter concludes by examining the LISP software architecture on various Cisco platforms.