IPv6 Site Multihoming Using a Host-based Shim Layer

Site multihoming is the process of an end-site, such as an enterprise, to obtain simultaneous IP connectivity from multiple ISPs, done for a number of reasons, such as increased resilience against failures. A new IETF working group was chartered at the end of June 2005 to work on designing an IPv6 site multihoming solution. A prevailing approach, called "shim6", inserts a shim layer between the IP and transport layer. Sites have to deploy multiple provider-assigned IP address prefixes from multiple ISPs on hosts, instead of a single providerindependent prefix. These IP addresses ("locators") are used by applications and if a session becomes inoperational, shim6 can switch to using a different address pair. The switch is transparent to applications as the shim layer rewrites and restores the addresses at the sending and receiving host. The solution has been designed with ease of deployment and transition in mind, and changes in typical applications are not required. We describe and analyze this solution, and as the design is still in progress so we note and analyze many open issues.