The Extcommunity-filter is used only in BGP. The extended community of BGP supports only the Route-Target (RT) extended community of Virtual Private Network (VPN). The Extcommunity-filter specifies matching rules for the extended community attribute.
You can use an extended community filter when using the route target (RT) attribute to filter routes in a VPN scenario.
ip extcommunity-filter { basic-extcomm-filter-num | basic basic-extcomm-filter-name } { deny | permit } { rt { as-number:nn | 4as-number:nn | ipv4-address:nn } } &<1-16>
or
ip extcommunity-filter { advanced-extcomm-filter-num | advanced advanced-extcomm-filter-name } { deny | permit } regular-expression