Technical Tip: Community lists in BGP to achieve logical 'AND' or 'OR' operations

[syao]

Description	This article explains how to use community lists in BGP to achieve logical 'AND' or 'OR' operations when matching prefixes with multiple BGP communities. This can help filter or manipulate routes based on specific combinations of community attributes.
Scope	FortiGate v6.2 or above.
Solution	Consider a situation where FortiGate is receiving the following BGP prefixes (1.1.1.1/32, 2.2.2.2/32, 3.3.3.3/32) with each containing community attributes. To match the community attribute of 100:100 OR 200:200, use the community list format as shown below: config router community-list     edit "OR"         config rule             edit 1                 set action permit                 set match "100:100"             next                 edit 2                     set action permit                     set match "200:200"                 next             end         next     end To match the community attribute of 100:100 AND 200:200,  use the community list format as shown below: config router community-list     edit "AND"         config rule             edit 1                 set action permit                 set match "100:100 200:200"             next         end     next end Additionally, it is possible to check the BGP prefixes that match the community list using the command 'get router info bgp network community-list <community-list-name>':