Is-Is - 3Com 7700 Configuration Manual

IS-IS

areas. RTB belongs to area0, which complies with the backbone area
membership requirement. However, RTC does not belong to area0.
Therefore, a virtual link must be set up between RTC and RTB to insure that
area2 and area0 (the backbone area) are connected.
Figure 8 OSPF Areas
area0
RTB
RTA
The backbone area (area0) cannot be configured as the STUB area and the
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virtual link cannot pass through the STUB area. So, if a virtual link has been
set up between RTB and RTC, neither area1 nor area0 can be configured as
a STUB area. Only area2 can be configured as a STUB area.
Routers in the STUB area cannot redistribute the external routes.
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Intermediate System-to-Intermediate System (IS-IS) intra-domain routing
information exchange protocol is the dynamic routing protocol used in the AS
issued by the International Organization for Standardization (ISO). In the OSI
model reference, IS equals the router in the TCP/IP model reference. The IS-IS
protocol, based on the link state algorithm, uses the Shortest Path First (SPF)
algorithm and it is highly like the Open Shortest Path First (OSPF) protocol.
The integrated IS-IS is an implementation of the IS-IS regulated by IETF on IP.
This section introduces IS-IS routing protocol terms.
Intermediate System (IS). IS equals a router of TCP/IP. It is the basic unit in IS-IS
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protocol used for propagating routing information and generating routes. In
the following text, IS shares the same meaning with the router.
End System (ES). It equals the host system of TCP/IP. ES does not process the
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IS-IS routing protocol, and therefore it can be ignored in the IS-IS protocol.
Routing Domain (RD). A group of ISs exchange routing information with the
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same routing protocol in a routing domain.
Area. Area is the division unit in the routing domain.
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Link State DataBase (LSDB). All the link states in the network form the LSDB. In
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an IS, at least one LSDB is available. The IS uses the SPF algorithm and the LSDB
to generate its own routes.
Link State Protocol Data Unit (LSP). In the IS-IS, each IS will generate an LSP
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which contains all the link state information of the IS. Each IS collects all the
LSPs in the local area to generate its own LSDB.
Network Protocol Data Unit (NPDU). It is the network layer packets of ISO and
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equals the IP packet of TCP/IP.
Designated IS (DIS), is the elected router on the broadcast network, equivalent
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to the DR in OSPF.
Network Service Access Point (NSAP) is the network layer address of ISO. It
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identifies an abstract network service access point and describes the very
network address for ISO model routing.
area1 area2
RTC
IS-IS 99
RTD