OSPF Virtual-links

• If area authentication is enabled, all interfaces which have adjacencies on them must authenticate.
• A virtual-link is an area 0 interface.
• The far end of the virtual link is the ABR [for area x range ...]
• Interface authentication is independent of area authentication, and interface authentication overrides area authentication. This means that you could be using clear-text authentication throughout and area, and implement md5 authentication on a particular link within that area.
• 'area 0 authentication', the remote router where the virtual-link terminates would also have to say 'area 0 authentication'. It is not necessary to configure a key on the interface (or virtual-link in this case). OSPF authentication uses a "null" key by default.