In RFC 6724 section 5 on "Source Address Selection" rule 2 says to "Prefer appropriate scope":

If Scope(SA) < Scope(SB): If Scope(SA) < Scope(D), then prefer SB and otherwise prefer SA. Similarly, if Scope(SB) < Scope(SA): If Scope(SB) < Scope(D), then prefer SA and otherwise prefer SB.

This rule does not seem to forbid selecting an address that has a smaller scope than the destination address.

Is this ever valid? If yes, can you give an example?

1 Answer 1


Sure, consider for example a LAN where global scope addresses are managed by DHCPv6 or manually and where the "A" bit is not set in router advertisements so hosts do not auto-configure global addresses (but do get the routes for on-link addresses). Now consider what happens when a host without a global address pings a global address on the same LAN.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.