Tag Switching, a technology developed by Cisco Systems, merges the intelligence of routing with the performance of layer 2 switching networks. It was designed for routed IP networks or switched ATM, Frame Relay and Ethernet networks. Tag switching relies on two principal components: forwarding and control. The forwarding component uses the tag information (tags) carried by packets and the tag-forwarding information maintained by a tag switch to perform packet forwarding. The control component is responsible for maintaining correct tag-forwarding information among a group of interconnected tag switches.

Tag Distribution Protocol (TDP) is proposed and used for this purpose. It has tagging algorithms that can tag packets for a specific destination or tagged to flow along specified routes for balancing loads. Basically, the process of tag switching is as follows:

• Edge device applies tag to packet
• Tag switches forward according to label swapping tables
• Edge device removes tag and forwards packet

Tag switching is replaced by Multi-Protocol label Switch (MPLS) technologies, which is the IETF standard combined advantages of multiple technologies such as Ipsillon IP switching, Cisco tag switching, IBM ARIS (Aggregate Route IP Switch) and Toshiba CSR (Cell Switched Router).

Tag Switch

Related Terms: multilayer switch, Layer 2 router, Layer 3 switch, IP switch, routing switch, switching router, wirespeed router, tag switch, MPLS Protocols, TDP

Reference Links: http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/tagswtch.htm: Tag Switching