From: Sabrina Dubroca <s...@queasysnail.net> Date: Wed, 28 Feb 2018 16:40:08 +0100
> According to RFC 4429 (section 3.1), adding new IPv6 addresses as > optimistic addresses is acceptable, as long as the implementation > follows some rules: > > * Optimistic DAD SHOULD only be used when the implementation is aware > that the address is based on a most likely unique interface > identifier (such as in [RFC2464]), generated randomly [RFC3041], > or by a well-distributed hash function [RFC3972] or assigned by > Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315]. > Optimistic DAD SHOULD NOT be used for manually entered > addresses. > > Thus, it seems reasonable to allow userspace to set the optimistic flag > when adding new addresses. > > We must not let userspace set NODAD + OPTIMISTIC, since if the kernel is > not performing DAD we would never clear the optimistic flag. We must > also ignore userspace's request to add OPTIMISTIC flag to addresses that > have already completed DAD (addresses that don't have the TENTATIVE > flag, or that have the DADFAILED flag). > > Then we also need to clear the OPTIMISTIC flag on permanent addresses > when DAD fails. Otherwise, IFA_F_OPTIMISTIC addresses added by userspace > can still be used after DAD has failed, because in > ipv6_chk_addr_and_flags(), IFA_F_OPTIMISTIC overrides IFA_F_TENTATIVE. > > Setting IFA_F_OPTIMISTIC from userspace is conditional on > CONFIG_IPV6_OPTIMISTIC_DAD and the optimistic_dad sysctl. > > Signed-off-by: Sabrina Dubroca <s...@queasysnail.net> > Reviewed-by: Stefano Brivio <sbri...@redhat.com> Applied, thank you.
