Lectures notes for 2010 - KTH

A Tag Edge router labels a packet based on its destination, then the Tag Switches
make their switching decision based on this tag, without having to look at the
contents of the packet.
The Tag Edge routers and Tag Switch exchange tag data using Tag Distribution
Protocol (TDP).
Basics of Tag switching:
1.Tag edge routers and tag switches use standard routing protocols to identify routes through the internetwork.
2.Using the tables generated by the routing protocols the tag edge routers and switches assign and distribute tag
information via the tag distribution protocol (TDP). When the Tag routers receive this TDP information they build a
forwarding database.
3.When a tag edge router receives a packet it analyzes the network layer header, performs applicable network layer
services, selects a route for the packet from its routing tables, applies a tag, and forwards the packet to the next hop tag
switch.
4.The tag switch receives the tagged packet and switches the packet based solely on the tag.
5.The packet reaches the tag edge router at the egress point of the network, the tag is stripped off and the packet delivered
as usual.
Maguire Cisco’s Tag Switching 7: 64 of 70
maguire@kth.se 2010.03.21 Internetworking/Internetteknik