Announcement : publicly available LISP and shim6 implementations


During the last years, there have been many discussions about the scalability of the Internet architecture notably within the IRTF RRG.
With IPv6, thanks to its huge addressing space, it is possible to design protocols and mechanisms that are more scalable and more powerful than with IPv4. A typical example is the multihoming problem. This problem occurs when a site is attached to several Internet Service providers. With IPv4, the classical solution is for the site to obtain one IPv4 prefix and advertise it by using BGP. This solution works and traffic engineering is possible, but unfortunately, it contributes to a significant growth of the BGP routing tables in the global Internet. With IPv6, the IETF decided to focus on a host-based technique. Basically, when a site is attached to n providers, each of its hosts will receive n different IPv6 addresses. This reduces the size of the BGP routing tables by avoiding to advertise the IPv6 prefixes used by the stub domains and provide many additional benefits in terms of path diversity or performance. Now that the shim6 standardization is being finalized by the IETF, it is time to validate this approach experimentally in the IPv6 Internet. Sebastien Barr´┐Ż has developed the first publicly available implementation of the shim6 IPv6 host-based multihoming on the Linux kernel. LinShim6 is available form

Other approaches to better scale the Internet architecture are being discussed, notably within the Routing Research Group of the Internet Research Task Force. Several of these approaches rely on separating the two roles of IP addresses: the locator role and the identifier role. In today's IPv4 Internet, IPv4 addresses are used both to indicate the location in the Internet topology of a host (the locator role) and to terminate the transport flows on end-hosts (the identifier role). This means that it is difficult to change the IP address of a host without disrupting transport flows.

The techniques that separate identifiers from locators take a different approach. First, an identifier is attached to each end-host. This identifier is used to terminate the transport flows. Second, each identifier may be reachable through multiple locators and a mapping mechanism is used to map an identifier (or a set of identifiers) onto a set of locators. This improves the scalability of the routing system as only the locators need to be distributed by BGP provided, of course, that the mapping system remains scalable. Furthermore, separating identifiers and locators has several additional benefits in terms of path diversity and performance. Some approaches propose to attach locators to hosts while other prefer to attach locators only to routers. The latter approach is the solution chosen by the proponents of the Locator/Identifier Separation Protocol (LISP). LISP is a router-based solution to solve the scaling problems of the Internet architecture that is currently being developed by Cisco.

There are still many open questions concerning notably the mapping between identifiers and locators. To allow researchers and network operators to experiment with LISP, the IP Networking Lab of UCLouvain releases OpenLISP. OpenLISP is the first publicly available implementation of LISP on the FreeBSD kernel. OpenLISP was designed and implemented by Luigi Iannone. You can find more details about OpenLISP from

Best regards,

Olivier Bonaventure