Ldp And Mpls - Nokia 7705 SAR-W Series Manual

MPLS Guide

5.1.1 LDP and MPLS

LDP performs dynamic label distribution in MPLS environments. The LDP operation
begins with a Hello discovery process network to form an adjacency with an LDP
peer in the network. LDP peers are two MPLS routers that use LDP to exchange
label/FEC mapping information. An LDP session is created between LDP peers. A
single LDP session allows each peer to learn the other's label mappings and to
distribute its own label information (LDP is bidirectional), and exchange label binding
information.
LDP signaling works with the MPLS label manager to manage the relationships
between labels and the corresponding FEC. For service-based FECs, LDP works in
tandem with the Service Manager to identify the virtual leased lines (VLLs) and
pseudowires (PWs) to signal.
An MPLS label identifies a set of actions that the forwarding plane performs on an
incoming packet before discarding it. The FEC is identified through the signaling
protocol (in this case LDP), and is allocated a label. The mapping between the label
and the FEC is communicated to the forwarding plane. In order for this processing
on the packet to occur at high speeds, optimized tables that enable fast access and
packet identification are maintained in the forwarding plane.
When an unlabeled packet ingresses the 7705 SAR, classification policies associate
it with a FEC, the appropriate label is imposed on the packet, and then the packet is
forwarded. Other actions can also take place on a packet before it is forwarded,
including imposing additional labels, other encapsulations, or learning actions. Once
all actions associated with the packet are completed, the packet is forwarded.
When a labeled packet ingresses the router, the label or stack of labels indicates the
set of actions associated with the FEC for that label or label stack. The actions are
performed on the packet and then the packet is forwarded.
The LDP implementation provides support for DU, ordered control, and liberal label
retention mode.
3HE 18686 AAAB TQZZA
• LDP Fast Reroute (FRR)
• LDP-to-Segment Routing Stitching for IPv4 /32 Prefixes (IS-IS)
• LDP FRR Remote LFA and TI-LFA Backup Using an SR Tunnel for IPv4 /32
Prefixes (IS-IS)
• TCP MD5 Authentication
Use subject to Terms available at: www.nokia.com
© 2022 Nokia.
Label Distribution Protocol
369