IS-IS - OSI Network Layer and Addressing

14 important questions on IS-IS - OSI Network Layer and Addressing

What is abreviation of ES and what is it uses for?

ES End system use for hosts

What does the therm (IS-IS)  System mean?

Network node

What is the abbreviation of CLNP and what does it mean?

ConnectionLess-mode Network Protocol

Connectionless mode operates like IP, pure datagram service without any prior session establishment


CLNP is like IPv4/IPv6
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What is the abbreviation for ITU-T?

International Telecommunication Union Telecommunications sector

What two parts does the NSAP address consist of?

-Initial Domain Part (IDP)
-Domain Specific Part (DSP)

What two fields does the IDP consist of?

AFI
IDI

What is the abbreviation for IDI and what does it mean?

Initial domain identifier

IDI field has variable length depending on the address format indicated by AFI and might be omitted.

What three fields does the DSP consist of?

-HO-DSP
-System-ID
-SEL

What is the abbreviation for HO-DSP and what does it mean?

High-Order Domain Specific part


An area part of a domain in which a node is located

What is the system-ID and what is the current implementation fixed lenght?

Unique identifier of the node

6 octets

AABB:CCDD:EEFF

Octet: AA

What is the abbreviation for (N)SEL?

NSAP Selector

What is the NSAP selector used for?

1-octed-long field that identifies the particular service in or above the network layer on the destination node that should process the datagram (In IP world like tcp)

In IP world would be particular protocol above IP, or the transport port

What does the SEL value indicates?

It indicates the transport protocol (eg 2F indicates GRE IP-over-CLNP tunneling)

What does the value 0 means for SEL and what does it mean?

No particular service is being addressed

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