DCN configurations
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Hierarchical routing
Hierarchical routing is used for large networks when the number of NSAP entries in
the RIB databases of the Intermediate Systems is too large. When this happens, it
causes an exponential increase of exchanged LSPs between Intermediate Systems. This
in turn causes the performance of the DCN to decrease due to the computation of the
shortest path first algorithm.
Hierarchical routing definition
In hierarchical routing, the DCN addressing domain is divided into a number of areas.
Each area is assigned a unique identifier. The value of the Area Identifier of each
node’s NSAP address is set according to the area the node is part of.
Level 1, Level 2 definition
Each area contains a number of:
• End Systems,
• first level (Level 1) Intermediate Systems and,
• second level (Level 2) Intermediate Systems.
Level 1 Intermediate Systems provide interconnectivity between nodes within the same
area. Level 2 Intermediate Systems provide interconnectivity between nodes belonging
to different areas.
Level 2 subdomain
The complete set of Level 2 Intermediate Systems is also referred to as the Level 2
Subdomain. All areas in a network are connected via the Level 2 Subdomain.
Area-divisioning of a DCN
Partitioning is configuration of the DCN in such a way that the exchange of LSPs
between Intermediate Systems is limited.
When networks are partitioned into areas, the RIB database(s) in the systems are much
smaller and hence the routing overhead is significantly reduced. Intermediate Systems
in an area only exchange information (LSPs) on nodes with other systems in their own
area. Information on other areas is exchanged by Level 2 Intermediate Systems only
and maintained by the Level 2 Intermediate Systems of the area.
In this way, the data management load in the network is strongly reduced, while
keeping the dynamic re-routing capabilities of Intermediate Systems in case of failures
intact. It is important to notice that although the DCN is divided into areas, ES-ES
communication between all nodes in the DCN is still possible.
The figure below illustrates how a network can be partitioned into areas, connected by
Level 2 Intermediate Systems. Each area has at least one Level 2 Intermediate System
assigned and can have a number of Level 1 Intermediate Systems and End Systems.
Management communication setup
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365-312-807R7.2
Issue 4, May 2007
Alcatel-Lucent - Proprietary
See notice on first page
4-7
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