Case 3—Limit Tag Distribution on a Tag Switching Network
The third case demonstrates the full control that is available to you in determining the destination prefixes and paths for which Tag Switching is enabled.
Configure the routers so that packets addressed to Network A are tagged, all other packets are untagged, and only links R1-R3, R3-R4, R4-R6, and R6-R7 carry tagged packets addressed to Network A. For example, suppose the normally routed path for packets arriving at R1 addressed to Network A or Network B is R1-R3-R5-R6-R7. A packet addressed to Network A would flow tagged on links R1-R3 and R6-R7, and untagged on links R3-R5 and R5-R6. A packet addressed to Network B would follow the same path, but would be untagged on all links.