Is-Is Routers; Network Entity Title (Net) Addresses - Siemens RUGGEDCOM ROX II User Manual

RUGGEDCOM ROX II
CLI User Guide
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
ISP 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.
The following sections describe IS-IS in more detail:
• Section 5.18.1.1, "IS-IS Routers"
• Section 5.18.1.2, "Network Entity Title (NET) Addresses"
• Section 5.18.1.3, "Advantages and Disadvantages of Using IS-IS"
Section 5.18.1.1

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.
Section 5.18.1.2

Network Entity Title (NET) Addresses

IS-IS routers are identified by their Network Entity Title (NET) address, which is in Network Service Access Point
(NSAP) format (RFC 1237
consist of the Authority and Format Identifier (1 byte), the Area ID (0 to 12 bytes), the System ID (6 bytes) and the
selector (1 byte).
The following is an example of an NSAP address:
NSAP address: 49.0001.1921.6800.1001.00
AFI: 49 (typical for IS-IS NET addresses)
Area ID: 0001 (typically 4 bytes)
System ID: 1921.6800.1001 (equates to the IP address 192.168.1.1)
Selector: 00 (NET addresses always have a selector of 00)
IS-IS Routers
RFC 1195
[http://tools.ietf.org/html/rfc1237]). NSAP addresses range from 8 to 20 octets and
[http://tools.ietf.org/html/rfc1195]. IS-IS is used primarily in
Chapter 5
Setup and Configuration
295