Cisco Active Network Abstraction Reference Guide, 3.7.1
Multiprotocol Label Switching
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Multiprotocol Label Switching

Table Of Contents

Multiprotocol Label Switching

Technology Description

MPLS

LDP

Information Model Objects (IMOs)

MPLS Interface

Label Switching Entity

Equivalent Label Switching Entry

MPLS Entry

MPLS Aggregate Entry

LDP Service

LDP Peer

LDP Peer Discovery Source

Vendor-Specific Inventory and IMOs

Network Topology

Service Alarms


Multiprotocol Label Switching


This chapter describes the level of support that Cisco ANA provides for MPLS, as follows:

Technology Description

Information Model Objects (IMOs)

Vendor-Specific Inventory and IMOs

Network Topology

Service Alarms

Technology Description

This section provides the following MPLS technology descriptions:

MPLS

LDP

Please see Part 1: Cisco VNEs in this guide for information about which devices support the various technologies.

MPLS

MPLS was originally presented as a way of improving the forwarding speed of routers. It is now emerging as a crucial standard technology that offers new capabilities for large-scale IP networks. Traffic engineering (TE), the ability of network operators to dictate the path that traffic takes through the network, and VPN support, are examples of two key applications where MPLS is superior to any currently available IP technology. It integrates Layer 2 information about network links (bandwidth, latency, utilization) into Layer 3 (IP) within a particular autonomous system, or ISP, in order to simplify and improve IP packet exchange. It also gives network operators a great deal of flexibility in how they divert and route traffic around link failures, congestion, and bottlenecks.

When packets enter an MPLS-based network, label edge routers (LERs) give them a label identifier. These labels not only contain information based on the routing table entries (for example, destination, bandwidth, delay, and other metrics), but also refer to the IP header field (source IP address), Layer 4 socket number information, and differentiated service. Once this classification is complete and mapped, different packets are assigned to corresponding label switched paths (LSPs), where label switch routers (LSRs) place outgoing labels on the packets.

LDP

Label Distribution Protocol (LDP) enables neighboring provider or provider-edge routers acting as LSRs in an MPLS-aware network to exchange label prefix binding information, which is required for forwarding traffic. The LSRs discover potential peers in the network with which they can establish LDP sessions in order to negotiate and exchange the labels (addresses) to be used for forwarding packets.

LDP supports two types of peer discovery:

Basic discovery—Used to discover directly connected LDP LSRs. An LSR sends hello messages to the "all routers on this subnet" multicast address, on interfaces for which LDP has been configured.

Extended discovery—Used between indirectly connected LDP LSRs. An LSR sends targeted hello messages to specific IP addresses. Targeted sessions must be configured since the routers are not physically connected and broadcasting would not reach the peers. The IP addresses of both peers are required for extended discovery.

Information Model Objects (IMOs)

This section describes the following IMOs:

MPLS Interface (IMpls)

Label Switching Entity (ILse)

Equivalent Label Switching Entry (ILSEEntries)

MPLS Entry (IMplsEntry)

MPLS Aggregate Entry (IMplsAggregateEntry)

LDP Service (ILdpService)

LDP Peer (ILdpPeer)

LDP Peer Discovery Source (ILdpPeerDiscoverySource)

MPLS Interface

The network/data link layer MPLS Interface object represents an MPLS configuration in a router interface. It is bound by its Containing Termination Points attribute to a data link layer interface object, and is accessed primarily by the Network layer IP Interface bound by its Contained Connection Termination Points attribute. It is also accessed by the Label Switching Entity.

Table 15-1 MPLS Interface (IMpls)  

Attribute Name
Attribute Description
Scheme
Polling Interval

Distribution Protocol

Distribution protocol (Null, LDP, TDP, RSVP, TDP and LDP)

IPCore

Configuration

Outer and Inner Labels

Outer and inner labels for Path Tracer

IPCore

Configuration

Traffic Engineering Properties

Traffic engineering properties (MPLS TE Properties)

IPCore

Configuration

Resource Reservation Properties

Resource Reservation Protocol properties

IPCore

Configuration

IANA Type

Internet Assigned Numbers Authority (IANA) type of the sublayer

N/A

N/A

Containing Termination Points

Underlying termination points (connection or physical)

IPCore

N/A

Contained Connection Termination Points

Bound connection termination points

IPCore

N/A


Label Switching Entity

The Label Switching Entity object describes the protocol-independent forwarding component of an LSR. It is bound by its Logical Sons attribute to all the network or data link layer MPLS Interface objects among which this Label Switching Entity is switching IP packets.

Table 15-2 Label Switching Entity (ILse) 

Attribute Name
Attribute Description
Scheme
Polling Interval

MPLS Table

Array of Equivalent Label Switching Entries between MPLS interfaces

IPCore

Configuration

MPLS Aggregate Table

Array of Equivalent Label Switching Entries from MPLS interfaces into VRF tables

IPCore

Configuration

MPLS Tunnel Segments

Array of switched MPLS TE tunnel segments (GUI usage) (see Multiprotocol Label Switching Traffic Engineering)

IPCore

Configuration

LDP Service

LDP Service which holds the LDP Peers

IPCore

Configuration

Logical Sons

Array of all MPLS Interfaces among which this Label Switching Entity is switching IP packets

IPCore

N/A


Equivalent Label Switching Entry

The Equivalent Label Switching Entry, MPLS Entry, and MPLS Aggregate Entry objects describe an MPLS Label Switching table's entries. Each is an array of MPLS Entries or MPLS Aggregate Entries sharing a single ingress label.

Table 15-3 Equivalent Label Switching Entry (ILSEEntries)  

Attribute Name
Attribute Description
Scheme
Polling Interval

Label Switching Entries

Array of either MPLS Entries or MPLS Aggregate Entries (sharing a single ingress label)

IPCore

Configuration


MPLS Entry

Table 15-4 MPLS Entry (IMplsEntry)  

Attribute Name
Attribute Description
Scheme
Polling Interval

Incoming Label

Incoming label

IPCore

Configuration

Outgoing Interface and Label

Outgoing interface and label

IPCore

Configuration

Switching Action

Switching action (Null, Pop, Swap, Aggregate, Untagged, Pop, Act)

IPCore

Configuration

Next Hop IP Address

Next hop IP address

IPCore

Configuration

Destination Mask

IP subnet mask of the destination

IPCore

Configuration

Destination Address

Destination IP address

IPCore

Configuration


MPLS Aggregate Entry

Table 15-5 MPLS Aggregate Entry (IMplsAggregateEntry)  

Attribute Name
Attribute Description
Scheme
Polling Interval

Virtual Routing Entity

Virtual Routing and Forwarding (VRF) entity

IPCore

Configuration

Incoming Label

Incoming label

IPCore

Configuration

Outgoing Interface and Label

Outgoing interface and label

IPCore

Configuration

Switching Action

Switching action (Null, Pop, Swap, Aggregate, Untagged, Pop, Act)

IPCore

Configuration

Next Hop IP Address

Next hop IP address

IPCore

Configuration


LDP Service

The LDP Service object, which is used in MPLS network environments, describes the main attributes of the LDP service. It is accessed only by the Label Switching Entity's LDP Service attribute.

Table 15-6 LDP Service (ILdpService)  

Attribute Name
Attribute Description
Scheme
Polling Interval

Local Identification

Local LDP identifier

IPCore

Configuration

Status

Service status (Unknown, Running, Down)

IPCore

Configuration

LDP Peers

Array of LDP Peers

IPCore

Configuration


LDP Peer

The LDP Peer object describes a remote LDP entity that currently has an LDP session with the Local LDP Service. The LDP Peer is bound to the LDP Service by the latter's LDP Peer attribute.

Table 15-7 LDP Peer (ILdpPeer) 

Attribute Name
Attribute Description
Scheme
Polling Interval

Peer Identification

Peer LDP identifier

IPCore

Configuration

Transport Addresses

Peer transport IP addresses

IPCore

Configuration

Distribution Method

Label distribution method (Unknown, Downstream, Downstream On Demand)

IPCore

Configuration

Protocol Type

Peer protocol type (Unknown, LDP, TDP)

IPCore

Configuration

Path Vector Limit

Path vector limit for loop detection

IPCore

Configuration

Session Status

LDP session status type (Transient, Initialized, Open Received, Open Sent, Operational)

IPCore

Configuration

Protocol Version

LDP session protocol version

IPCore

Configuration

Hold Time

Hold time for maintaining the session without receiving traffic or keepalive

IPCore

Configuration

Hello Time Interval

Time interval at which hello (Keep Alive) packets should be sent

IPCore

Configuration

Peer Discovery Sources

Array of LDP Peer Discovery Sources

IPCore

Configuration


LDP Peer Discovery Source

The LDP Peer Discovery Source object describes the discovery source of the LDP Peer. Identification of the Peer is done using broadcast on MPLS Interfaces and a hello message exchanged between LSRs.

Table 15-8 LDP Peer Discovery Source (ILdpPeerDiscoverySource)  

Attribute Name
Attribute Description
Scheme
Polling Interval

Interface Name

MPLS interface name on which the peer was discovered

IPCore

Configuration

Source Addresses

Source IP addresses from which the hello message was sent

IPCore

Configuration

Type

Discovery type (Link, Targeted)

IPCore

Configuration


Vendor-Specific Inventory and IMOs

There are no vendor-specific inventory or IMOs for this technology.

Network Topology

Cisco ANA discovers MPLS network layer topology by searching for the existence of the local IP subnet in any one-hop-away remote side's MPLS Interface. In particular, it compares the local and remote IP subnets gathered from the upper IP network layers.

Service Alarms

The following alarms are supported for this technology:

Broken LSP Discovered, page 41-11

MPLS Black Hole Found, page 41-47

MPLS Interface Removed, page 41-48

LDP Neighbor Loss, page 41-41