Virtual Links

Virtual Links

• Used to connect an area to the backbone thru another area.
• Configuration uses router-id.
• Used to connect discontinuous Area O's.
• Any discontinuous area is a bad idea.
• If authentication is configured on Area O it must be configured on the far end virtual link router. Use " Area O authentication " on remote end

Nested Virtual Links

• You can extend to more than one area away.
• One Hope at a time.
• As you install Virtual link, you bring Area O outwards to the remote area.

OSPF without Area O

• In a single area system, Area O is not needed.
• Once you have more than one area, Area O is required.
• A virtual link by itself is part of Area O.
• To make a virtual link come up though, some area must exist in Area 0 already.
• Loopbacks work perfectly fine.

Link Metrics

• Router advertised dont include local link.
• Received Router have local link cost added.
• Frequently use " SH IP RO OS" to see changes.
• May influence simple path changes on Per Router Basis.
• May influence Area exit point choices if multiple ABR's exist.
• Use "SH IP O I | IN IS UP | COST"