requirements. If multiple LSP exclusions are configured in the attribute-set, they can be added to the path
message along with an appropriate LSP connection diversity sub-object.
Path Message without an ERO
In GMPLS UNI, UNI-C nodes send a request for a connection to UNI-N node. The connection request does
not contain an end-to-end path, because, UNI-C nodes do not have knowledge of the topology of the optical
network and therefore cannot determine the end-to-end path. The UNI-C node signals a connection request
without an ERO.
When no ERO is present in a received path message, the UNI-N node calculates a route to the destination and
includes that route in an ERO, before forwarding the path message. If no route is found, the UNI-N returns a
path error message with an error code and subcode of
24,5 - "No route available toward destination"
.
The destination address of a GMPLS LSP can be either the optical router-id of the tail UNI-C node, or the
optical address of the ingress interface to the tail UNI-C node. Supplying the router-id allows the UNI-N to
route the tunnel to the tail UNI-C node via any attached UNI-N node; supplying the UNI-C's ingress interface
address forces the tunnel's path to traverse the UNI-N node attached to that interface.
The optical router-ids and interface addresses may or may not be the same as the packet ones.
Note
XRO Attribute-set
An optional XRO attribute-set can be specified as part of the path-option to specify LSP diversity requirements.
An empty XRO attribute set results in the GMPLS tunnel being signaled with no exclusions, and therefore
no XRO.
A non-existent XRO attribute-set can be configured in the GMPLS UNI tunnel path-option; in this case
no attempt will be made to bring up the GMPLS tunnel until the configuration is complete.
Note
Connection Diversity
Connection diversity is required to ensure that GMPLS tunnels can be established without sharing resources,
thus, greatly reducing the probability of simultaneous connection failures. For example, an edge-node wishes
to establish multiple LSPs towards the same destination edge-node, and these LSPs need to have few or no
resources in common.
Connection diversity supports the establishment of a GMPLS LSP which is diverse from the path taken by
an existing LSP. An XRO is added to the tunnel's path message with appropriate LSP diversity sub-objects
or exclusions. A maximum of 20 connection diversity exclusions per XRO is supported.
GMPLS RSVP VRF Signaling
The Cisco IOS XR software supports a single non-default VRF for the GMPLS RSVP signaling. This allows
GMPLS signaling to work even when the only available communication between the UNI-C and UNI-N
Cisco IOS XR MPLS Configuration Guide for the Cisco CRS Router, Release 5.1.x
373
Implementing GMPLS UNI
GMPLS RSVP VRF Signaling
