MPLS Guide MPLS and RSVP-TE
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Therefore, both RSVP-TE and the IGP-TE (that is, OSPF-TE or IS-IS-TE for the
7705 SAR) must be enabled and running simultaneously.
The following TE capabilities are supported:
• hop limit — the hop limit is the maximum number of LSRs that a given LSP can
traverse, including the ingress and the egress LERs. Typically, the hop limit is
used to control the maximum delay time for mission-critical traffic such as voice
traffic.
The hop limit applies to the primary LSP, any backup LSPs, and LSPs
configured to be used in Fast Reroute (FRR) situations.
• admin groups — administrative groups provide a way to define which LSR
nodes should be included or excluded while signaling an LSP. For example, it
might be desirable to avoid some nodes or links that are known to be used
heavily from being included in the path of an LSP, or to include a specific LSR
node to ensure that a newly signaled RSVP-TE tunnel traverses that LSR node.
Administrative groups apply to both primary and secondary LSPs. They are
defined under the config>router>if-attribute context, and are applied at the
MPLS interface level, as well as at the LSP and the primary and secondary LSP
levels through include and exclude commands.
• bandwidth — the bandwidth capability (supported by RSVP-TE), is similar to the
Connection Admission Control (CAC) function in ATM. During the establishment
phase of RSVP-TE, the LSP PATH message contains the bandwidth reservation
request. If the requested capacity is available, the RESV message confirms the
reservation request. The amount of reserved bandwidth stated in the request is
deducted from the amount of reservable bandwidth for each link over which the
LSP traverses.
The bandwidth capability applies to both primary and secondary LSPs, and
LSPs configured to be used in Fast Reroute (FRR) situations.
3.3.1.3 Hello Protocol
The Hello protocol detects the loss of a neighbor node (node failure detection) or the
reset of a neighbor’s RSVP-TE state information. In standard RSVP, neighbor
monitoring occurs as part of the RSVP soft-state model. The reservation state is
maintained as cached information that is first installed and then periodically
refreshed by the ingress and egress LERs. If the state is not refreshed within a
specified time interval, the LSR discards the state because it assumes that either the
neighbor node has been lost or its RSVP-TE state information has been reset.
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