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ME60 V800R010C10SPC500 Feature Description - WAN Access 01

This is ME60 V800R010C10SPC500 Feature Description - WAN Access
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Active-Route-Advertise

Active-Route-Advertise

Background

Active-route-advertise allows a device to advertise only optimal routes in an IP routing table.

Active-route-advertise prevents changes to data forwarding paths that may occur after independent BGP route selection is deployed. Independent BGP route selection enables a device to advertise an optimal BGP route in a BGP routing table to BGP peers, regardless of whether this optimal BGP route is optimal in an IP routing table. Therefore, if a device is upgraded to support independent BGP route selection, previously selected data forwarding paths may change. If you do not expect the changes, configure active-route-advertise on the device.

Related Concepts

IP routing table: stores routes that are optimal in each available protocol routing table, selects optimal routes from the stored routes, and delivers the selected optimal routes to the forwarding information base (FIB) table.

Independent BGP route selection: enables a device to advertise an optimal BGP route in a BGP routing table to BGP peers, regardless of whether this optimal BGP route is optimal in an IP routing table.

Implementation

As shown in Figure 9-34, an RR is deployed between Device A and Device B, an Open Shortest Path First (OSPF) neighbor relationship is established between Device A and the RR, an External BGP (EBGP) peer relationship is established between Device B and Device C, and Device A and Device C are not directly connected.

Figure 9-34 Active-route-advertise networking diagram

The route 100.0.0.0/8 is imported to the BGP and OSPF routing tables on Device A, and the RR learns both the BGP route 100.0.0.0/8 and OSPF route 100.0.0.0/8. By default, an OSPF route has a higher priority over a BGP route. Therefore, the OSPF route 100.0.0.0/8 is an optimal route in the IP routing table, and the BGP route 100.0.0.0/8 is inactive in the IP routing table. Table 9-3 describes the changes after the RR is upgraded to support independent BGP route selection, including the changes in the optimal route in the BGP routing table, route advertisement, and data forwarding path.

Table 9-3 Change description

Item

In the Source Version

In the Target Version Without Active-Route-Advertise

In the Target Version with Active-Route-Advertise

Optimal route in the BGP routing table

The BGP route 100.0.0.0/8 is an optimal route in the BGP routing table, but not optimal in the IP routing table.

Route advertisement

Independent BGP route selection is not supported. The RR does not advertise the BGP route 100.0.0.0/8 to Device B. Device C learns routes advertised by Device E but not by Device B.

Independent BGP route selection is supported. The RR advertises the BGP route 100.0.0.0/8 to Device B. Device C learns routes advertised by both Device B and Device E.

The BGP route 100.0.0.0/8 is not an optimal route in the IP routing table on the RR. The RR does not advertise the BGP route 100.0.0.0/8 to Device B. Device C learns routes advertised by Device E but not by Device B.

Available data forwarding path

Link B

Link A and Link B

Link B

Actually selected data forwarding path

Device C selects Link B to send data to 100.0.0.0/8.

Device C selects Link A to send data to 100.0.0.0/8.

Device C selects Link B to send data to 100.0.0.0/8.

As described in Table 9-3, active-route-advertise ensures that the data forwarding path Link B is still used after independent BGP route selection is deployed.

NOTE:

Before you configure active-route-advertise, check whether BGP routes are optimal routes in the IP routing table. If all BGP routes are optimal routes in the IP routing table, data forwarding paths do not change after active-route-advertise is configured. If only some BGP routes are optimal routes in the IP routing table, analyze the impacts of active-route-advertise and determine whether to configure this feature.

Advantages

Active-route-advertise prevents changes to data forwarding paths that may occur after independent BGP route selection is deployed.

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Updated: 2019-01-04

Document ID: EDOC1100059473

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