Virtual Private LAN Services
7750 SR OS Services Guide Page 487
SDP Usage
Service Access Points (SAP) are linked to transport tunnels using Service Distribution Points
(SDP). The service architecture of the 77507450 platform allows services to be abstracted from
the transport network.
MPLS transport tunnels are signaled using the Resource Reservation Protocol (RSVP-TE) or by
the Label Distribution Protocol (LDP). The capability to automatically create an SDP only exists
for LDP based transport tunnels. Using a manually provisioned SDP is available for both RSVP-
TE and LDP transport tunnels. Refer to the appropriate OS MPLS Guide for more information
about MPLS, LDP, and RSVP.
Automatic Creation of SDPs
When BGP AD is used for LDP VPLS and LDP is used as the transport tunnel there is no
requirement to manually create an SDP. The LDP SDP can be automatically instantiated using the
information advertised by BGP AD. This simplifies the configuration on the service node.
Enabling LDP on the IP interfaces connecting all nodes between the ingress and the egress builds
transport tunnels based on the best IGP path. LDP bindings are automatically built and stored in
the hardware. These entries contain an MPLS label pointing to the best next hop along the best
path toward the destination.
When two endpoints need to connect and no SDP exists, a new SDP will automatically be
constructed. New services added between two endpoints that already have an automatically
created SDP will be immediately used. No new SDP will be constructed. The far-end information
is gleaned from the BGP next hop information in the NLRI. When services are withdrawn with a
BGP_Unreach_NLRI, the automatically established SDP will remain up as long as at least one
service is connected between those endpoints. An automatically created SDP will be removed and
the resources released when the only or last service is removed.
Manually Provisioned SDP
The carrier is required to manually provision the SDP if they create transport tunnels using RSVP-
TE. Operators have the option to choose a manually configured SDP if they use LDP as the tunnel
signaling protocol. The functionality is the same regardless of the signaling protocol.
Creating a BGP AD enabled VPLS service on an ingress node with the manually provisioned SDP
option causes the Tunnel Manager to search for an existing SDP that connects to the far-end PE.
The far-end IP information is gleaned from the BGP next hop information in the NLRI. If a single
SDP exists to that PE, it is used. If no SDP is established between the two endpoints, the service
will remain down until a manually configured SDP becomes active.
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