IP Routing : All routers within domains that carry transit traffic have to maintain both interior and exterior routing information. Problem: Additional resource required by the routers Increasing routing convergence time. Tag Switching :
All routers within domains that carry transit traffic have to maintain both interior and exterior routing information.
Additional resource required by the routers
Increasing routing convergence time
Complete decoupling of interior and exterior routing
Tag switches within the domain just maintain routing information provided by interior routing.
Tag switches on the border of a domain maintain both exterior and interior routes.
Reduces the routing load on nonborder switches and shortens routing convergence time.Hierarchy of Routing Knowledge
ib switch: ingress border tag switch
eb switch: egress border tag switch
Packet Tag Stack
tag binding direction
packet travel direction
limits the ability to influence the actual paths taken by packets
limits the ability to distribute traffic evenly
limits ISP’s ability to segregate different classes with respect to the links used by those classes.
not adequate to routing with resource reservations
routing with resource reservations (Qos routing)
allows installation of tag binding in tag switches that do not corresponding to the destination-based routing pathsFlexible Routing