## 6 Benefits and Deployment Considerations of GLI-Split
### Implementation and Deployment Considerations  
The GLI-Split functionality inside upgraded GLI-nodes requires host updates that could be distributed via operating system updates. The modification introduces an additional shim layer between the network layer and the transport layer, which performs the vertical address translation (see Section 3.2), as well as mapping registration and mapping lookups for outgoing packets (see Section 3.3.2). The modifications inside hosts do not require changes to transport layer protocols like TCP, as the horizontal address translation done by the shim layer is transparent to upper layers.  
In the initial deployment phase, host updates are not necessarily required for all nodes in a GLI-domain, as GLI-Split also accommodates classic IPv6 nodes (see Section 4.3). To achieve this accommodation, a modified DNS is required which returns either a local or a global address, depending on whether source and destination host are in the same or different GLI-domains (see Section 4.3.1). The modification, however, does not require changes to the DNS protocol, as it could be realized via configuring a split-horizon or split-view DNS that provides different DNS records, depending on the location of the querying source host. The only protocol modification that is required is the extension of the DHCPv6 protocol, which is used for the assignment of local addresses to hosts inside GLI-domains (see Section 3.2.2). The DHCP needs to return the address of the local and global mapping service which could be realized via a new DHCP options field, as is currently done for DNS server addresses. A new DHCP options field may also be used to return a set of global locators to upgraded GLI-nodes. For classic IPv6 nodes, the DHCP needs to know the ID and MAC address to compute local GLI-addresses with checksum compensation. In addition, the DHCP is responsible to register the advertised local GLI-addresses in the local mapping service and the corresponding global GLI-addresses in the global mapping service (see Section 3.2.2), which requires an extension of the DHCP server functionality.  
The most critical entity in GLI-Split is the GLI-gateway which implements the main network functionality. It is responsible for the horizontal address translation (see Section 3.2) as well as for all mapping service related mechanisms like mapping registration or mapping lookups. Furthermore, it realizes all mechanisms which are required to support classic IPv6 nodes in GLI-domains (see Section 4.3). The complexity of such a GLI-gateway is comparable to a common NAT-gateway, which also translates addresses and recomputes TCP checksums. NAT functionality is, in the current Internet, mostly used in residential home gateways or in carrier-grade or large scale NAT solutions in provider networks. Large scale NAT solutions are, for instance, used in the IPv6 transition mechanisms like NAT444 [47]. Hence, we assume that the complexity of the GLI-Split mechanisms can be handled by available off-the-shelf routing hardware. In addition, we assume that GLI-gateways are located closer to the edge which also reduces the size of GLI-domains and thus the amount of traffic that must be handled by GLI-gateways.