HPE FlexNetwork HSR6800 Configuration Manual page 142

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GR helper—A neighbor of the GR restarter. It helps the GR restarter to complete the GR
process.
After an IS-IS GR restarter restarts, it must complete the following tasks to synchronize the LSDB
with its neighbors:
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Obtain IS-IS neighbor information without changing adjacencies.
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Obtain the LSDB.
To complete these tasks, the GR restarter sends an OSPF GR signal to GR helpers so that the GR
helpers keep their adjacencies with the GR restarter, and restores the neighbor table after receiving
responses from neighbors. The GR restarter then synchronizes the LSDB with all GR-capable
neighbors, calculates routes, updates its routing table and forwarding table, and removes stale
routes. The IS-IS routing convergence is then complete.
IS-IS NSR
Nonstop routing (NSR) is a new feature that overcomes the application limit of GR:
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In standalone mode, NSR backs up IS-IS link state information from the active MPU to the
standby MPU. When an active/standby MPU switchover occurs, NSR can complete link state
recovery and route regeneration without requiring the cooperation of other devices.
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In IRF mode, NSR backs up IS-IS link state information from the global active MPU to the global
standby MPU. When a global active/standby MPU switchover occurs, NSR can complete link
state recovery and route regeneration without requiring the cooperation of other devices.
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 must get the traffic attributes of
all links in the local area. The traffic engineering information of links is obtained from IS-IS. For more
information about configuring IS-IS TE, see MPLS Configuration Guide.
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. Because one LSP carries a limited amount
of link state information, 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 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.
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Terms:
Originating system—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 IS-IS process that
originally runs.
System ID—The 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.
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