BGP extended communities attribute is introduced with MPLS VPN/BGP technology. MPLS VPN/BGP expands capability of network infrastructure to provide VPN functionality. At the same time it requires a new framework for policy routing. With BGP Extended Communities Attribute we can use Route Target or Site of Origin for implementing network policy for MPLS VPN/BGP.
BGP Extended Communities Attribute is similar to BGP Communities Attribute. It is an optional transitive attribute. BGP Extended Communities Attribute can carry multiple Extended Community value. Each Extended Community value is eight octet length.
BGP Extended Communities Attribute provides an extended range compared with BGP Communities Attribute. Adding to that there is a type field in each value to provides community space structure.
There are two format to define Extended Community value. One is AS based format the other is IP address based format.
ASpart is 2 octets Global Administrator subfield in Extended Community value.
VALpart is 4 octets Local Administrator subfield.
7675:100represents AS 7675 policy value 100.
IP-Addresspart is 4 octets Global Administrator subfield.
VALpart is 2 octets Local Administrator subfield.