3Com S7906E Configuration Manual page 725

IS-IS TE
IS-IS Traffic Engineering (TE) creates and maintains the Label Switched Path (LSP).
When creating the Constraint-based Routed LSP (CR LSP), MPLS needs to get the traffic attribute
information of all links in the local area. The Traffic Engineering information of links is obtained from
IS-IS.
For detailed configuration of the IS-IS TE, refer to MPLS TE Configuration in the MPLS Volume.
Management tag
Management tag simplifies routing information management by carrying the management information
of the IP address prefixes (to control route redistribution from other routing protocols) and BGP
community and extended community attributes.
LSP fragment extension
IS-IS advertises link state information by flooding LSPs. One LSP carries a limited amount of link state
information; therefore, IS-IS fragments LSPs. Each LSP fragment is uniquely identified by a
combination of the System ID, Pseudonode ID (0 for a common LSP or a non-zero value for a
Pseudonode LSP), and LSP Number (LSP fragment number) of the node or pseudo node that
generated the LSP. The one-byte LSP Number field, allowing a maximum of only 256 fragments to be
generated by an IS-IS router, limits the amount of link information that the IS-IS router can advertise.
The LSP fragment extension feature allows an IS-IS router to generate more LSP fragments. Up to 50
additional virtual systems can be configured on the router, and each virtual system is capable of
generating 256 LSP fragments to enable the IS-IS router to generate up to 13056 LSP fragments.
1) Terms
Originating System
It is the router actually running IS-IS. After LSP fragment extension is enabled, additional virtual
systems can be configured for the router. Originating system is the actual IS-IS process that originally
runs.
System ID: System ID of the originating system.
Additional System ID
Additional virtual system IDs are configured for the IS-IS router after LSP fragment extension is enabled.
Each additional system ID can generate 256 LSP fragments. Both the additional system ID and the
system ID must be unique in the entire routing domain.
Virtual System
A virtual system is identified by an additional system ID and generates extended LSP fragments.
Original LSP
It is the LSP generated by the originating system. The system ID in its LSP ID field is the system ID of
the originating system.
Extended LSP
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