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CLI-based Configuration Guide - IP Unicast Routing

AR100, AR120, AR150, AR160, AR200, AR1200, AR2200, AR3200, and AR3600 V200R010

This document describes the concepts and configuration procedures of IP Service features on the device, and provides the configuration examples.
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OSPF Traffic Engineering (TE) is a new feature developed on the basis of OSPF to support MPLS TE and establish and maintain the Label Switch Path (LSP) of TE. In the MPLS TE architecture described in "Principles" in the Configuration Guide - MPLS - MPLS TE Configuration, OSPF functions as the information advertising component, responsible for collecting and advertising MPLS TE information.

In addition to the network topology, TE also needs to know network constraints, such as the bandwidth, TE metric, administrative group, and affinity attribute. Current OSPF functions, however, cannot meet these requirements. Therefore, OSPF needs to be extended by introducing a new type of LSAs to advertise network constraints. Based on the network constraints, the Constrained Shortest Path First (CSPF) algorithm can calculate the path that satisfies certain constraints.

Figure 5-7 Function of OSPF in the MPLS TE architecture

Function of OSPF in the MPLS TE Architecture

In the MPLS TE architecture, OSPF functions as the information advertising component:

  • Collects related information about TE.

  • Floods TE information to devices in the same area.

  • Uses the collected TE information to form the TE database (TEDB) and provides it for CSPF to calculate routes.

OSPF does not consider what the specific information is or how MPLS uses the information.


OSPF uses a new type of LSAs, namely, Type 10 opaque LSAs, to collect and advertise TE information. This type of LSAs contains the link status information required by TE, including the maximum link bandwidth, maximum reservable bandwidth, current reserved bandwidth, and link color. Type 10 opaque LSAs synchronize link status information among devices in an area through the OSPF flooding mechanism. By so doing, a uniform TEDB is formed for route calculation.

Interaction Between OSPF TE and CSPF

OSPF collects TE information in an area by using Type 10 LSAs, including the bandwidth, priority, and link metric. After processing the collected TE information, OSPF provides it for CSPF to calculate routes.

IGP Shortcut and Forwarding Adjacency

OSPF supports IGP shortcut and forwarding adjacency. The two features allow OSPF to use a tunnel interface as an outgoing interface to reach a destination.

Differences between IGP shortcut and forwarding adjacency are as follows:

  • A device enabled with IGP shortcut uses a tunnel interface as an outgoing interface, but it does not advertise the link of the tunnel interface to neighbors. Therefore, other devices cannot use this tunnel.

  • A device enabled with forwarding adjacency uses a tunnel interface as an outgoing interface, and advertises the tunnel interface to neighbors. Therefore, other devices can use this tunnel.

  • IGP shortcut is unidirectional and needs to be configured only on the device that uses IGP shortcut.


DiffSer Aware Traffic Engineering (DS-TE) controls and forwards flows differently based on Class of Service (CoS). DS-TE combines the advantages of MPLS TE and Differentiated Services (DiffServ) and controls flow paths precisely. By so doing, DS-TE effectively uses network resources and reserves required resources for different service flows. For details, see "Principles" in the Configuration Guide - MPLS - MPLS TE Configuration.

To support DS-TE in MPLS, OSPF supports the local overbooking multiplier TLV and bandwidth constraint (BC) TLV in the TE-LSA, which are used to advertise and collect the reservable bandwidths of class types (CTs) with different priorities on the link (A CT refers to a collection of bandwidths of an LSP or a group of LSPs with the same CoS.)


OSPF supports the applications of the Shared Risk Link Group (SRLG) in MPLS by obtaining information about the SRLG that floods TE information to devices in an area. For details, see "Principles" in the Configuration Guide - MPLS - MPLS TE Configuration.

Updated: 2019-05-20

Document ID: EDOC1100034072

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