Service Manual

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Intermediate System to Intermediate System
Intermediate system to intermediate system (Is-IS) is supported on Dell Networking OS.
• IS-IS is supported on the S3048–ON with Dell Networking Operating System (OS) 9.7(0.1)
•
• The IS-IS protocol is an interior gateway protocol (IGP) that uses a shortest-path-rst algorithm. Dell Networking supports both
IPv4 and IPv6 versions of IS-IS.
• The IS-IS protocol standards are listed in the Standards Compliance chapter.
IS-IS Protocol Overview
The IS-IS protocol, developed by the International Organization for Standardization (ISO), is an interior gateway protocol (IGP) that
uses a shortest-path-rst algorithm.
NOTE: This protocol supports routers passing both IP and OSI trac, though the Dell Networking implementation
supports only IP trac.
IS-IS is organized hierarchically into routing domains and each router or system resides in at least one area. In IS-IS, routers are
designated as Level 1, Level 2 or Level 1-2 systems. Level 1 routers only route trac within an area, while Level 2 routers route trac
between areas. At its most basic, Level 1 systems route trac within the area and any trac destined for outside the area is sent to
a Level 1-2 system. Level 2 systems manage destination paths for external routers. Only Level 2 routers can exchange data packets
or routing information directly with external routers located outside of the routing domains. Level 1-2 systems manage both inter-area
and intra-area trac by maintaining two separate link databases; one for Level 1 routes and one for Level 2 routes. A Level 1-2 router
does not advertise Level 2 routes to a Level 1 router.
To establish adjacencies, each IS-IS router sends dierent protocol data units (PDU). For IP trac, the IP addressing information is
included in the IS-IS hello PDUs and the link state PDUs (LSPs).
This brief overview is not intended to provide a complete understanding of IS-IS; for that, consult the documents listed in Multi-
Topology IS-IS.
IS-IS Addressing
IS-IS PDUs require ISO-style addressing called network entity title (NET).
For those familiar with name-to-network service mapping point (NSAP) addresses, the composition of the NET is identical to an
NSAP address, except the last byte is always 0. The NET is composed of the IS-IS area address, system ID, and N-selector. The last
byte is the N-selector. All routers within an area have the same area portion. Level 1 routers route based on the system address
portion of the address, while the Level 2 routers route based on the area address.
The NET length is variable, with a maximum of 20 bytes and a minimum of 8 bytes. It is composed of the following:
• area address — within your routing domain or area, each area must have a unique area value. The rst byte is called the
authority and format indicator (AFI).
• system address — the router’s MAC address.
• N-selector — this is always 0.
The following illustration is an example of the ISO-style address to show the address format IS-IS uses. In this example, the rst ve
bytes (47.0005.0001) are the area address. The system portion is 000c.000a.4321 and the last byte is always 0.
Intermediate System to Intermediate System
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