Multiple topology-transparent zones having a common edge node

A method for virtualizing topology transparent zones (TTZs) in a network area, the network area having a first TTZ and a second TTZ, comprising:

• generating a link between a network node and an edge node of the first TTZ, wherein the network node is an edge node of both the first and the second TTZs;
• generating one or more first link state advertisements (LSAs) including description of the first link and an external link between the network node and an external node that is external to the first and second TTZs;
• generating one or more second LSAs including description of the first link and the external link;
• sending the one or more first LSAs to the external node;
• and
• sending the one or more second LSAs to an internal node of the second TTZ, wherein the internal node of the second TTZ is outside of the first TTZ,
• wherein the internal node of the second TTZ and a second internal link of the second TTZ between the network node and the internal node of the second TTZ are hidden from the external node and an internal node of the first TTZ, the internal node of the first TTZ being outside of the second TTZ.

A network system for virtualizing topology transparent zones (TTZs) in a network area, the network area having a first TTZ and a second TTZ, comprising:

• a network node as an edge node of both the first and the second TTZs;
• an edge node of the first TTZ;
• an external node that is external to the first and second TTZs;
• an internal node of the second TTZ, the internal node of the second TTZ being outside of the first TTZ;
• and
• an internal node of the first TTZ, the internal node of the first TTZ being outside of the second TTZ,
• wherein the network node is configured to
• generate a first link between the network node and the edge node of the first TTZ,
• generate one or more first link state advertisements (LSAs) including description of the first link and an external link between the network node and the external node,
• generate one or more second LSAs including description of the first link and the external link,
• send the one or more first LSAs to the external node, and
• send the one or more second LSAs to the internal node of the second TTZ,
• wherein a second internal link of the second TTZ between the network node and the internal node of the second TTZ and the internal node of the second TTZ are hidden from the external node and the internal node of the first TTZ.