Siemens RUGGEDCOM ROX II User Manual page 488

Chapter 13
Unicast and Multicast Routing
• Section 13.6.9, "Managing the Lifetime of LSPs"
• Section 13.6.10, "Managing LSP Refresh Intervals"
• Section 13.6.11, "Managing Network Entity Titles (NETs)"
• Section 13.6.12, "Managing Redistribution Metrics"
Section 13.6.1
IS-IS Concepts
IS-IS is an Interior Gateway Protocol (IGP) meant to exchange information within Autonomous Systems (AS). It is
designed to operate within an administrative domain or network using link-state information to decide optimal
data packet routing, similar to OSPF. IS-IS floods the network with link-state information and builds a database of
the network's topology. The protocol computes the best path through the network (using Dijkstra's algorithm) and
then forwards packets to their destination along that path.
Although it was originally designed as an ISO Connectionless-mode Network Protocol (CLNP), it was later adapted
for IP network use (Dual IS-IS) in
environments and better suited to stringy networks as opposed to central core based networks.
NOTE
In complex legacy networks, RIP, OSPF, BGP and IS-IS may all be active on the same router at the same
time. Typically, however, only one dynamic routing protocol is employed at one time.
CONTENTS
• Section 13.6.1.1, "IS-IS Routers"
• Section 13.6.1.2, "Network Entity Title (NET) Addresses"
• Section 13.6.1.3, "Advantages and Disadvantages of Using IS-IS"
Section 13.6.1.1
IS-IS Routers
IS-IS routers can be defined as Level-1, Level-2, or both. Level 1 routers form the area, while Level 2 routers form
the backbone of the network. By default, RUGGEDCOM ROX II configures areas to be both (or Level-1-2). This
allows the device to inter-operate between different areas with minimal configuration.
• Level-1 routers are intra-area routers. They maintain a single Link-State Database (LSD) that only contains
information about the Level-1 and Level-2 neighbors in its area. To communicate with routers in another area,
Level-1 routers forward traffic through their closest Level-2 router.
• Level-2 routers are inter-area routers, meaning they can communicate with routers in other areas. They also
maintain a single LSD, but it only contains information about other Level-2 routers from the router's area or
other areas. The router knows nothing about the Level-1 routers in its area.
• Level-1-2 routers are both inter- and intra-area routers, meaning they can communicate with Level-1 and
Level-2 routers in any area. They maintain separate LSDs for Level-1 and Level-2 routers in and outside the
router's area.
442
RFC 1195 [http://tools.ietf.org/html/rfc1195]. IS-IS is used primarily in ISP
RUGGEDCOM ROX II
CLI User Guide
IS-IS Concepts