Tag Switching - Overview

What is tag switching ? Well, it is this thing that speeds up the net by "tagging" the packets so network devices can forward the packets to their destinations quickly. It involves tag edge routers, tag switches, and tag distribution protocol (tdp). What would it do to ease the network managers' lives ? It has tagging algorithms that can tag packets for a specific destination or tagged to flow along specified routes for balancing loads.

Although tag switching has been submitted to the IETF for standardization, different vendors can implement it in such a way that provides maximum benefits for their equipment. For example, Cisco's implementation in IOS 11.1CT or later features the following:

• Tag switch path tunnels (tsp tunnels): create alternative paths or connections between source and destination
• Traffic engineering: define traffic that will traverse a tsp tunnel
• Ships in the night: support atm and tag switching services simultaneously on the same atm backbone
• Tag distribution protocol: assign tags to routes and communicate assignments to peers. Runs in conjunction with layer 3 routing protocols.
• Dynamic tag switching: allocate and distribute tags based on routing topology discovered by layer 3 protocols. Runs in conjunction with layer 3 routing protocols
• Static tag switching: allocate and distribute tags based on RSVP signaling
• Support for ospf, is-is, rip, and eigrp: build routing topology used by the tag distribution protocol
• tag switch controller: enables bpx 8620 and 8650 to participate in a tag switching network

Tag information can be carried in a packet in many ways:

• As a small "shim" tag header inserted between the layer and the network layer headers
• As part of the layer header if the layer header provides sufficient semantics
• As part of the network layer header using the flow label field in ipv6 with properly modified semantics

Any media type including point-to-point links, multi-access links, and atm can use tag switching.

Since this is just an overview, the specifics will be discuss in a future article. So we have all this good stuff but what about actually using it ?

Case in point, let us look at an example. Suppose we have company abc who wants to migrate to use tag switching. This company has a switch environment and will use routers with tag switching to scale up. One of the solution is the following:

Some of the configurations are done under the interface prompt:

(config-if)#tag-switching ?
   ip                   Configure IP dynamic Tag Switching
   mtu                Set tag switching Maximum Transmission Unit
   tsp-tunnels     Configure TSP tunnels