IPv6 DHCP offers do not contain an IP prefix. The IPv6 prefix is usually obtained from the IPv6 RA arriving from the upstream router. For ZTP, the 7750 SR is a host; therefore, the system assigns a /128 prefix to the IPv6 address obtained from the DHCP offer.
The 7750 SR supports the use of an IPv6 RA to install IPv6 default and static routes from upstream routers. The system installs all the routes advertised using the RA. If the same route has been advertised from multiple upstream routers (next hops), the system installs the route with the highest preference. The 7750 SR does not support ECMP if the same route is advertised from multiple next hops by multiple RAs.
In accordance with RFC 4861 recommendations, the 7750 SR ensures that all RAs are obtained before the auto-provisioning process is started for IPv6. RFC 4861 recommends that the host (in this case, the 7750 SR) send a minimum of three route solicitations to increase the likelihood of at least one route solicitation being received by the upstream routers.
Each route solicitation is followed by a 4-second timeout, so the third route solicitation is sent 8 seconds after the first. The upstream routers must respond within 0.5 seconds. As a result, the 7750 SR receives all RAs and routes within 8.5 seconds of the first route solicitation, and waits a maximum of 9 seconds to receive all RAs; ZTP always waits 20 seconds to receive all RAs, however, only the first RA received is used.