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8-28 neighbor { ip-address peer- group - name } send-communitySyntax Description:
Purpose: By default, BGP community attributes are not advertised to peers. The neighbor send-community command enables the sending of BGP community attributes to BGP peers. Routing policies can be based on a neighbor address, a peer group name, or AS path information. Situations might arise in which you need to apply policies to routes that do not have any of the previously mentioned attributes in common. A community value is a numerical value or set of values that can be attached to a BGP route. Routing policies can then be applied to routes that contain a particular community value or attribute. Cisco IOS Software Release: 10.3. The peer-group-name option was added in Release 11.0. Configuration Example: NO-EXPORT Community ValueTwo well-known community values are NO-EXPORT and NO-ADVERTISE. If a route carries the NO-EXPORT community value, the route is not advertised outside the AS. The behavior of the NO-EXPORT community value is illustrated in Figure 8-29. The NO-ADVERTISE community value prevents a router from advertising the route to any peer, as shown in Figure 8-30. To configure a COMMUNITY attribute, we will use an outbound route map on Router A, as shown in the following configuration. For a complete discussion of route maps, see Appendix C. Figure 8-29. NO-EXPORT Community
Figure 8-30. NO-ADVERTISE Community
Router A router bgp 65530 network 172.16.0.0 mask 255.255.255.0 network 172.16.1.0 mask 255.255.255.0 network 172.16.2.0 mask 255.255.255.0 network 172.16.3.0 mask 255.255.255.0 neighbor 10.1.1.2 remote-as 1 neighbor 10.1.1.2 send-community neighbor 10.1.1.2 route-map setnoexport out ! access-list 1 permit 172.16.1.0 0.0.0.255 ! route-map setnoexport permit 10 match ip address 1 set community no-export route-map setnoexport permit 20 __________________________________________________________________________ Router B router bgp 1 neighbor 10.1.1.1 remote-as 65530 neighbor 10.1.2.2 remote-as 2 __________________________________________________________________________ Router C router bgp 2 neighbor 10.1.2.1 remote-as 1 For this configuration, Router B should receive the four 172.16 prefixes from Router A. Because the 172.16.1.0 prefix has the NO_EXPORT community value, Router B should not advertise this route to Router C. Verify the effect of the NO_EXPORT community value by checking the BGP tables on Routers B and C: rtrB# show ip bgp BGP table version is 41, local router ID is 10.1.1.2 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 10.1.1.1 0 0 65530 i *> 172.16.1.0/24 10.1.1.1 0 0 65530 i *> 172.16.2.0/24 10.1.1.1 0 0 65530 i *> 172.16.3.0/24 10.1.1.1 0 0 65530 i __________________________________________________________________________ rtrC# show ip bgp BGP table version is 41, local router ID is 10.1.2.2 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.0.0/24 10.1.2.1 0 0 1 65530 i *> 172.16.2.0/24 10.1.2.1 0 0 1 65530 i *> 172.16.3.0/24 10.1.2.1 0 0 1 65530 i The community values of routes can be checked using the show ip bgp community command: rtrB# show ip bgp community no-export BGP table version is 41, local router ID is 10.1.1.2 Status codes: s suppressed, d damped, h history, * valid, > best, i - internal Origin codes: i - IGP, e - EGP, ? - incomplete Network Next Hop Metric LocPrf Weight Path *> 172.16.1.0/24 10.1.1.1 0 0 65530 i Troubleshooting
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