## 1 Introduction  
Typical BGP (border gateway protocol) routing tables in the default-free zone (DFZ) of the Internet currently hold about 400,000 entries and continue to grow ever faster [1]. This has been recognized as a potential threat for the Internet's scalability in the future [2]. The expansion of the current IPv4 Internet is at its limits as the pool of free IPv4 addresses is already exhausted [3]. We believe that this will lead to increased IPv6 deployment. IPv6 has room for a multitude of addresses and might cause an immense growth of the routing table sizes in the DFZ. Hence, at least for the IPv6 Internet, a new and more scalable routing architecture is required. Separating current IP addresses into two independent pieces of reachability and identification information helps to reduce this growth and is called locator/identifier split (Loc/ID split) [4]. The stable identifier (ID) gives a global name to a node. A changeable locator (Loc) describes how the node can currently be reached through the global Internet. Furthermore, a mapping system (MS) is needed to map locators to identifiers. This principle makes routing in the stable Internet core more scalable because core routing is not affected by changed attachment points and multihoming of edge networks. The deployment of Loc/ID split in the Internet requires modifications to the current routing and addressing architecture. Its development takes a long time and implies hardware and software upgrades. Therefore, the modified Internet architecture should also satisfy additional requirements like support for renumbering, multihoming, multipath transmission, or security [5, 6]. Most of the current proposals for a future routing and addressing architecture [7] implement a kind of Loc/ID split. They essentially separate core and edge routing, but local routing is still performed on IDs. When nodes change their position within a local routing domain, or move from one edge network to another, they either require a new ID or the local routing system must account for that change. Replacing a node's ID breaks the function of an ID and adapting the local routing system makes routing more complex. A few proposals implement a true Loc/ID split, e.g., [8], but they take a clean-slate approach, _i.e_., they are not backward-compatible with today's Internet which makes them difficult to deploy. This work proposes GLI-Split as a new concept for future Internet routing and addressing. It splits the functionality of IP addresses into global locators, local locators, and identifiers and implements a true Loc/ID split with IDs that are independent of the current location. IDs and locators are encoded in regular IPv6 addresses so that no new routing protocols are required. GLI-Split is backward-compatible with the IPv6 Internet and interworking is simple. GLI-Split, however, does more than only solve the scalability problem. It also has several compelling benefits: it facilitates provider changes, renumbering, multihoming, multipath-routing, traffic engineering, and provides improved mobility support. To take full advantage of all features, nodes in GLI-domains require upgraded networking stacks, but legacy nodes can also be accommodated in GLI-domains and enjoy benefits. This facilitates incremental deployability. For interworking between GLI-Split and the IPv4 Internet, we can use existing mechanisms for IPv4 and IPv6, as GLI-Split is IPv6-compatible. This paper is structured as follows. Section 2 presents general building blocks for new addressing schemes, gives a high-level introduction to GLI-Split, and discusses related works. Section 3 presents fundamentals of GLI-Split and explains how GLI-Split works with upgraded and non-upgraded nodes in single-homed domains. Section 4 then introduces mechanisms required for the multihomed case and describes how multipath transfer and traffic engineering can be supported. Section 5 briefly introduces our implementation of the GLI-Split architecture and presents a proof-of-concept evaluation with respect to the round-trip-time.