Introduction

Overview

The IS-IS routing protocol an interior gateway protocol (IGP) that is used for routing within a single domain. If the domain contains a large number of nodes, nodes must be split into a number of logical areas. IS-IS Level 1 Routing provides routing between nodes and other Layer 1 routers within a single area. IS-IS Level 2 Routing provides routing between the other Layer 2 routers in the network areas that compose the domain.

Support of Level 2 routing by Alcatel-Lucent 1850 TSS-5 means that it can be used to support routing between areas within large domains.

Both the assignment of NEs to areas and the enabling of NEs as Level 2 routers is accomplished by provisioning (refer to Network services access point and Level 2 routing, respectively).

OSI node vs. Network Element terminology

Each Alcatel-Lucent 1850 TSS-5 is an NE that functions as a single OSI node. Some NEs support multiple OSI nodes in a single device. So, the term OSI node, when used to describe network size, may not correspond with the number of NEs in that network.

Symbols

The graphical examples is this appendix use the symbols that are defined in the following figure. The following figure illustrates an example network with nodes assigned to four different areas connected by Level 2 routers.

Figure 6-8: Network with Level 2 routers