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RSVP Elements
1
LSRs make a bandwidth reservation on a per-LSP basis. Only Controlled-Load
service
requests are supported. When bandwidth is requested, it is possible for the the LSP to
be established, even when the requested bandwidth is not reserved. You must verify
that the requested bandwidth was actually reserved. In cases when the bandwidth
reserved is less than the amount requested, you can manually tear down the LSP and
resignal it using a different path. CSPF is not supported. To specify a best effort LSP,
configure the reserved bandwidth as zero.
Bandwidth Accounting
ExtremeWare RSVP-TE supports the accounting of bandwidth reserved. The available
bandwidth specified in the Adspec object is not modified when the path message is
forwarded to the LSP endpoint. As reserve messages are processed, the reserved
bandwidth specified in the Flowspec is added to the total reserved bandwidth for the
appropriate VLANs. LSP path message setup and hold priorities are not used to
preempt previously established LSPs established through an Extreme LSR.
ExtremeWare does not support SE style labels. Therefore, increasing the reserved
bandwidth parameter for an LSP will force the LSP to be torn down. If the LSP is torn
down, the LSP is resignaled with the new reserved bandwidth value. There are no
guarantees that the LSRs along the path will be able to accommodate the increased
bandwidth reservation request.
RSVP State
State is installed at each device traversed by the path message, but no resources are
reserved. Among other things, the state identifies the adjacent RSVP nodes, which
describes the path for the reservation. Resources are not actually reserved until the
receiver responds to the path message with a reserve message.
Upon receiving a path message, a destination may examine the Tspec and the AdSpec
from the sender, in conjunction with local status/policy information, to determine the
actual QoS specification that is to be included in the reserve message. The reserve
message follows the reverse of the path established by the path message and the
appropriate resources are reserved at each node.
The state maintained by RSVP is temporary, or soft. Consequently, path and reserve
messages must be periodically retransmitted to maintain an active reservation. Soft
state is advantageous because it naturally adapts to changing network conditions, such
1.
Controlled Load service is defined in RFC 2211.
MPLS Module Installation and User Guide
5-7
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