bgp-ls (OSPF view)

Function

The bgp-ls identifier command configures an OSPF topology ID.

The undo bgp-ls identifier command deletes an OSPF topology ID.

The bgp-ls enable command enables OSPF topology advertisement to BGP.

The undo bgp-ls enable command disables OSPF topology advertisement to BGP.

By default, the OSPF topology ID is 0.

By default, OSPF topology advertisement to BGP is disabled.

Format

bgp-ls enable

bgp-ls identifier identifier-value

undo bgp-ls enable

undo bgp-ls identifier [ identifier-value ]

Parameters

Parameter	Description	Value
identifier identifier-value	Specifies an OSPF topology ID.	The value is an integer ranging from 2 to 65535.

Parameter

Description

Value

identifier identifier-value

Specifies an OSPF topology ID.

The value is an integer ranging from 2 to 65535.

Views

OSPF view

Default Level

2: Configuration level

Task Name and Operations

Task Name	Operations
ospf	write

Usage Guidelines

Usage Scenario

Each BGP node identifies topologies based on their IDs and reports topology information to the controller.

The topology information saved on all OSPF devices in the same area is the same. Therefore, the topology information about the area can be reported to the controller as long as BGP-LS is enabled on one BGP node. Deploying BGP-LS on two BGP nodes is recommended because they can back up each other. If BGP-LS is deployed on more than one node, identifier-value must remain the same on all these nodes to ensure that the collected topology information is correct.

BGP-LS is a new method of collecting topology information.

Without BGP-LS, forwarders use an IGP (OSPF or IS-IS) to collect topology information of each AS, and the IGP reports the information to the controller. This topology information collection method has the following disadvantages:

The controller must have high computing capabilities and support the IGP and its algorithm.
The controller cannot gain the complete inter-AS topology information and therefore is unable to calculate optimal E2E paths.
Different IGPs report topology information separately to the controller, which complicates the controller's analysis and processing.
With powerful routing capabilities of BGP, BGP-LS has the following advantages:
Reduces computing capability requirements and spares the necessity of IGPs on the controller.
Facilitates route selection and calculation on the controller by using BGP to summarize and report process or AS topology information to the controller.
Requires only one routing protocol to report topology information to the controller.
To enable OSPF topology advertisement to BGP, run the bgp-ls enable command. The topology information that OSPF reports to BGP includes node, link, and prefix information.

Prerequisites

OSPF topology advertisement to BGP has been enabled using the bgp-ls enable command.

Implementation Procedure

OSPF topology information can be flooded only within an area. As a result, the controller can obtain OSPF topology information about only one area. To address this problem, deploy at least one BGP node in each OSPF area and establish a BGP peer relationship between each BGP node and the controller so that BGP-LS collects and reports topology information to the controller.

Configuration Impact

BGP-LS advertises all topology information (node, link, and prefix information), and the controller needs to save all topology information, consuming a large number of memory resources.
Any change in the topology information collected by BGP-LS will trigger LSA flooding, which may burden the controller. As a result, the maximum number of OSPF neighbors supported and the topology size will be affected.
BGP-LS requires topology synchronization between OSPF and BGP, which further consumes CPU resources. As a result, OSPF convergence is slowed down.

Precautions

The bgp-ls enable command is inapplicable to VPN views.

Example

# Enable OSPF topology advertisement to BGP and set the OSPF topology ID to 20.

<HUAWEI> system-view
[~HUAWEI] ospf
[*HUAWEI-ospf-1] bgp-ls enable
[*HUAWEI-ospf-1] bgp-ls identifier 20

# Enable OSPF topology advertisement to BGP.

<HUAWEI> system-view
[~HUAWEI] ospf
[*HUAWEI-ospf-1] bgp-ls enable