3com 3031 Instruccion De Instalación
524
C
HAPTER
41: I
NTEGRATED
IS-IS C
ONFIGURATION
IS-IS circumvents the above problem by a process called ‘Route Leaking’. This is the
process by which Level-2 routes are advertised into the Level-1 routing domain,
allowing the Level-1 routers to build a more comprehensive Link State Database.
process by which Level-2 routes are advertised into the Level-1 routing domain,
allowing the Level-1 routers to build a more comprehensive Link State Database.
Address Structure of
IS-IS Routing Protocol
Address Structure
Figure 135 Address structure of IS-IS protocol
ISO adopts the address structure as shown in the above figure, namely NSAP,
which consists of Initial Domain Part (IDP) and Domain Specific Part (DSP).
Stipulated in ISO, IDP specifies the authority, who assigns other parts of an
address, as well as the format that an address adopts. DSP is assigned by the
specified entity in IDP. The length of IDP and DSP is variable, but their total length
is of 20 bytes at most.
which consists of Initial Domain Part (IDP) and Domain Specific Part (DSP).
Stipulated in ISO, IDP specifies the authority, who assigns other parts of an
address, as well as the format that an address adopts. DSP is assigned by the
specified entity in IDP. The length of IDP and DSP is variable, but their total length
is of 20 bytes at most.
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Area Address
IDP consists of Authority and Format Indicator (AFI) and Initial Domain Identifier
(IDI). AFI decides the format of IDI. DSP is formed by multiple bytes. IDP, along
with HO-DSP of DSP, can identify both a routing domain and areas in a routing
domain; therefore, (IDP, HO-DSP) as a whole is also called an Area Address.
(IDI). AFI decides the format of IDI. DSP is formed by multiple bytes. IDP, along
with HO-DSP of DSP, can identify both a routing domain and areas in a routing
domain; therefore, (IDP, HO-DSP) as a whole is also called an Area Address.
Generally speaking, a router only needs to be configured with one area
address. Moreover, all the nodes in the same area have the same area address.
In order to support seamless combination, division and transformation of areas,
a router can be configured with 3 area addresses at most.
address. Moreover, all the nodes in the same area have the same area address.
In order to support seamless combination, division and transformation of areas,
a router can be configured with 3 area addresses at most.
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System ID
A system ID is used to uniquely identify an ES or a router in an area. Its length is
optional, being 48 bits (6 bytes). Normally, a Router_ID is adopted to
correspond with a system ID.
optional, being 48 bits (6 bytes). Normally, a Router_ID is adopted to
correspond with a system ID.
Suppose a router takes the IP address 168.10.1.1 of the interface Loopback0 as
its Router_ID, then its System ID used in IS-IS can be transformed with the
following method:
its Router_ID, then its System ID used in IS-IS can be transformed with the
following method:
Extend every part of the IP address 168.10.1.1 to 3 bits. Add 0 to the front of
the part that includes less than 3 bits.
the part that includes less than 3 bits.
Divide the extended address 168.010.001.001 into 3 parts, with each part
consisting of 4 digits.
consisting of 4 digits.
The reconstructed 1680.1000.1001 is just the System ID.
Actually, there are many ways to designate a System ID, as long as it can
uniquely identify an ES or a router.
uniquely identify an ES or a router.
AFI
IDI
High Order DSP
SyStem ID
SEL
(1 octet)
DSP
IDP
Area Address