Cisco Cisco IOS Software Release 12.0(22)S

Multiprotocol label switching (MPLS) is a packet forwarding technology that uses a short, fixed-length 
value called a label in packets to determine the next hop for packet transport through an MPLS network 
by means of label switching routers (LSRs). 

A fundamental MPLS principle is that LSRs in an MPLS network must agree on the definition of the 
labels being used for packet forwarding operations. Label agreement is achieved in an MPLS network 
by means of procedures defined in the Label Distribution Protocol (LDP). 

LDP operations begin with a discovery (Hello) process during which an LDP entity (a local LSR) finds 
a cooperating LDP peer in the network and negotiates basic operating procedures between them. The 
recognition and identification of a peer by means of this discovery process results in an Hello adjacency, 
which represents the context within which label binding information is exchanged between the local 
LSR and its LDP peer. LDP functionality then creates an active LDP session between the two LSRs to 
effect the exchange of label binding information. The result of this process, when carried to completion 
with respect to all the LSRs in an MPLS network, is a label switched path (LSP), which constitutes an 
end-to-end packet transmission pathway between the communicating network devices. 

By means of LDP, LSRs can collect, distribute, and release label binding information to other LSRs in 
an MPLS network, thereby enabling the hop-by-hop forwarding of packets in the network along 
normally routed paths. 

The MPLS LDP MIB has been implemented to enable standard, SNMP-based network management of 
the label switching features in Cisco IOS. Providing this capability requires SNMP agent code to execute 
on a designated network management station (NMS) in the network. The NMS serves as the medium for 
user interaction with the network management objects in the MPLS LDP MIB. 

The SNMP agent embodies a layered structure that is compatible with Cisco IOS and presents a network 
administrative and management interface to the objects in the MPLS LDP MIB and, thence, to the rich 
set of label switching capabilities supported by Cisco IOS. 

By means of an SNMP agent, you can access MPLS LDP MIB objects using standard SNMP GET 
operations to accomplish a variety of network management tasks. All the objects in the MPLS LDP MIB 
follow the conventions defined in the Internet Engineering Task Force (IETF) draft MIB entitled 
draft-ietf-mpls-ldp-mib-07.txt, which defines network management objects in a structured and 
standardized manner. This draft MIB is continually being evolved toward the status of a standard. 
Accordingly, the MPLS LDP MIB will be implemented in a manner that tracks the evolution of this IETF 
document. 

Slight differences that exist between the IETF draft MIB and the implementation of equivalent functions 
in Cisco IOS require some minor translations between the MPLS LDP MIB objects and the internal data 
structures of Cisco IOS. Such translations are accomplished by the SNMP agent, which runs in the 
background on the NMS workstation as a low priority process.

The extensive label switching capabilities supported in Cisco IOS provide an integrated approach to 
managing the large volumes of traffic carried by wide area networks (WANs). These capabilities are 
integrated into the Layer 3 network services, thus optimizing the routing of high volume traffic through 
Internet service provider backbones while, at the same time, ensuring the resiliency of the network to 
link or node failures.

This release of Cisco IOS supports the following functionality in relation to the MPLS LDP MIB:

Generation and sending of event notification messages to signal changes in the status of 
LDP sessions.

Enabling and disabling of event notification messages by means of extensions to existing SNMP CLI 
commands.