Downstream Tag Allocation Scheme

For each route in its FIB a switch:
- allocates a tag
- creates an entry in its TIB with the incoming tag set to the allocated tag
- advertises binding between the incoming tag and the route to all of the adjacent switches
When a switch receives tag binding information for a route, if the information was received from the next hop for that route, the switch places the tag into the outgoing tag of the TIB entry associated with the route