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ME60 V800R010C10SPC500 Feature Description - WAN Access 01

This is ME60 V800R010C10SPC500 Feature Description - WAN Access
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Community Attribute

Community Attribute

A community is a set of destination addresses with the same characteristics. It is four bytes long. On the ME60, the community attribute is expressed in the format of aa:nn or as a community number.

  • aa:nn: aa indicates an AS number and nn indicates the community identifier defined by an administrator. The value of aa or nn ranges from 0 to 65535, which is configurable. For example, if a route is from AS 100 and the community identifier defined by the administrator is 1, the community is 100:1.

  • Community number: It is an integer ranging from 0 to 4294967295. As defined in standard protocols, numbers from 0 (0x00000000) to 65535 (0x0000FFFF) and from 4294901760 (0xFFFF0000) to 4294967295 (0xFFFFFFFF) are reserved.

The community attribute is used to simplify the application, maintenance, and management of routing policies. With the community attribute, a group of BGP peers in multiple ASs can share the same routing policy. The community attribute is a route attribute. It is transmitted between BGP peers and is not restricted by the AS. Before advertising a route with the community attribute to peers, a BGP peer can change the original community attribute of this route.

The peers in a peer group share the same policy, while the routes with the same community attribute share the same policy.

The well-known communities are described in the next section. Users can also create their own communities to filter routes.

Well-known Community

Table 9-1 lists well-known communities of BGP routes.

Table 9-1 Well-known communities of BGP routes

Community Name

Community Identifier

Description

Internet

0

(0x00000000)

By default, all routes belong to the Internet community. A route with this attribute can be advertised to all BGP peers.

No_Export

4294967041 (0xFFFFFF01)

A route with this attribute cannot be advertised beyond the local AS.

No_Advertise

4294967042 (0xFFFFFF02)

A route with this attribute cannot be advertised to any other BGP peers.

No_Export_Subconfed

4294967043 (0xFFFFFF03)

A route with this attribute cannot be advertised beyond the local AS or to other sub-ASs.

Usage Scenario

On the network shown in Figure 9-8, EBGP connections are established between Device A and Device B, and between Device B and Device C. If the community attribute of No_Export is configured on Device A and Device A sends a route with the community attribute to Device B, Device B does not advertise the route to other ASs after receiving it.

Figure 9-8 Networking for BGP communities

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Updated: 2019-01-04

Document ID: EDOC1100059473

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