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RSVP Features
Route Recording
The route a path takes can be recorded. Recording the path allows the ingress LER to
know, on a hop-by-hop basis, which LSRs the path traverses. Knowing the actual path
of an LSP can be especially useful for diagnosing various network issues.
Network path recording is configurable per path. If enabled, the record route object
(RRO) is inserted into the path message using a single RRO subobject, representing the
ingress LER. When a path message is received by an Extreme LSR that contains an
RRO, an RRO IPv4 subobject representing the /32 address of the outgoing interface of
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the path message is pushed onto the top
of the first RRO. If the setup of an LSP
originates from an Extreme LER for which route recording is enabled, the path message
is originated with an RRO containing a single RRO subobject specifying the outgoing
interface address of the path message. The updated RRO is returned in the reservation
message.
The label recording flag is not supported by Extreme LSRs. This flag instructs all LSRs
along the LSP to include the advertised downstream label in a label object as part of the
RRO. If an Extreme LSR receives a path message with the label recording flag set in the
RRO, the LSR does not push a label subobject onto the RRO.
If a path message is received that contains an RRO, the Extreme LSR uses the RRO to
perform loop detection. The RRO is scanned to verify that the path message has not
already traversed this LSR. If the RRO contains an IPv4 subobject that represents a local
LSR interface, the path message is dropped and a "Routing Problem" error message is
sent to the originating LER with an error value of "Loop detected."
Explicit Route Path LSPs
An explicit route is a specified path through a routed network topology. The path may
be strictly or loosely specified. If strictly specified, each node or group of nodes along
the path must be configured. Thus, no deviation from the specified path is allowed.
Loosely specified paths allow for local flexibility in fulfilling the requested path to the
destination. This feature allows for significant leeway by the LSR in choosing the next
hop when incomplete information about the details of the path is generated by the LER.
Each node along the path may use other metrics to pick the next hop along the path,
such as bandwidth available, class of service, or link cost.
1.
RRO is organized as a LIFO stack.
MPLS Module Installation and User Guide
5-11
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