5.7 Summary

5.7 Summary

Tag Switching is an approach to label switching that seeks to address many of the problems described in Chapter 1 . These include enhancing routing functionality and improving the scalability and stability of routing. In this respect it has a broader set of goals than the other approaches described so far. It also addresses IP/ATM integration and performance issues.

Tag Switching takes advantage of the flexibility provided by the label switching forwarding component by supporting in its Control Component a wide spectrum of forwarding granularities. At one end of the spectrum, Tag Switching allows FECs to be identified with address prefixes or even whole groups of prefixes, which is essential for providing scalable routing. Tag Switching also allows FECs to be associated with a source/destination address pair. This is essential for supporting multicast with Tag Switching. By associating FECs with a combination of source address, destination address, transport protocol, source port, and destination port, Tag Switching provides support for RSVP and application flows. Finally, Tag Switching allows association with FECs based on purely local rules in order to support explicit routes according to local policy.

Tag Switching allows any number of different FECs to coexist in a single TSR, as long as these FECs provide unambiguous (with respect to that TSR) partitioning of the universe of packets that could be seen by the TSR.

One of the key innovations of Tag Switching is the use of a hierarchy of tags, organized as a tag stack. This enables enhancements...

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Switching in IP Networks: IP Switching, Tag Switching, & Related Technologies

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