Adjacency establishment

In the router, the adjacency management is done through the establishment of a Service Distribution Path (SDP) object, which is a service entity in the Nokia service model.

The Nokia service model uses logical entities that interact to provide a service. The service model requires the service provider to create configurations for four main entities:

customers
services
Service Access Paths (SAPs) on the local routers
Service Distribution Points (SDPs) that connect to one or more remote routers

An SDP is the network-side termination point for a tunnel to a remote router. An SDP defines a local entity that includes the system IP address of the remote routers and a path type. Each SDP comprises:

the SDP ID
the transport encapsulation type, either MPLS or GRE
the far-end system IP address

If the SDP is identified as using LDP signaling, then an LDP extended Hello adjacency is attempted.

Note: If the tldp option is selected as the mechanism for exchanging service labels over an MPLS or GRE SDP and the T-LDP session is automatically established, an explicit T-LDP session that is subsequently configured takes precedence over the automatic T-LDP session. However, if the explicit, manually-configured session is then removed, the system does not revert to the automatic session and the automatic session is also deleted. To address this, recreate the T-LDP session by disabling and re-enabling the SDP using the shutdown and no shutdown commands. To address this in MD-CLI, recreate the T-LDP session by using the admin-state command to administratively disable and then enable the SDP.

If another SDP is created to the same remote destination, and if LDP signaling is enabled, no further action is taken, because only one adjacency and one LDP session exists between the pair of nodes.

An SDP is a unidirectional object, so a pair of SDPs pointing at each other must be configured in order for an LDP adjacency to be established. When an adjacency is established, it is maintained through periodic Hello messages.