Cisco BGP - see communities on advertised-routes?



Border Gateway Protocol (BGP) is a routing protocol used in large networks, such as those of Internet Service Providers (ISPs). BGP is used to carry out path selection and routing decisions based on a variety of factors, such as the origin of the route, the path length, and the administrative weight assigned to each route. BGP also allows for the attachment of additional information to routes, known as BGP Communities. This can be used to limit the propagation of routes between ISPs, as well as to identify routes that belong to a specific group of networks (e.g. customers of a particular ISP).

In order to view BGP Communities associated with a particular route, you need to first enable BGP Community display on the device. This can be done with the command ‘show ip bgp community ’, where is the IP address prefix of the route (e.g. 192.168.0.0/24).

Once BGP Community display is enabled, you can use the ‘show ip bgp neighbors advertised-routes’ command to view the routes advertised by a particular BGP neighbor. This command will also display the BGP Communities associated with each route.

In addition to viewing the BGP Communities associated with a route, you can also view the BGP Communities associated with a particular BGP neighbor. This can be done with the ‘show ip bgp neighbors community’ command. This will display all of the BGP Communities that have been configured for that neighbor.

Finally, you can also view the BGP Communities associated with a particular network. This can be done with the ‘show ip bgp community’ command, where is the IP address prefix of the network (e.g. 192.168.0.0/24). This will display all of the BGP Communities configured for that network.

In summary, BGP Communities can be used to limit the propagation of routes between ISPs, as well as to identify routes that belong to a specific group of networks. To view BGP Communities associated with a particular route, you need to first enable BGP Community display on the device, and then use the ‘show ip bgp neighbors advertised-routes’ command. You can also view the BGP Communities associated with a particular BGP neighbor or network by using the ‘show ip bgp neighbors community’ or ‘show ip bgp community’ commands, respectively.

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