IS-IS - IS-IS packet - Link State PDUs

10 important questions on IS-IS - IS-IS packet - Link State PDUs

What is the abbreviation of link state PDU and what does it?

Link state protocol data unit (LSP). LSP is vaguely similar to an OSPF link State Update packet containing one or more link state advertisements.

Used to advertise routing information

What are the three parts that identify IS-IS LSPs? 3

-System ID
-Pseudonode ID
-LSP Number

What is the Pseudonode ID used for?

Differentiates between LSP describing the router itself and the LSPs for multiaccess network in which the router is a Designated IS (1 octet)
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What is the LSP number used for?

Denoting (aanduiden) the fragment number of this LSP (1 octet). The LSP number is also called simply the fragment number or fragment for short.

What is the abbreviation of LSPID and what does it consist of?

Link state PDU ID

-System ID + Pseudonode ID + LSP Number

If the TLV exceed the MTU. How are TLV's advertised?

Route create multiple LSP's

LSP's are identified with same System and Pseudonode ID, but with
an increasing LSP number as the fragment number starting with 0.

On what device is fragmentation of the LSP performed?

Only on the router that originates the LSP.

What is the IS-IS command to show the system-id and the related hostname?

show isis hostname

R1# show isis hostname
Level System ID Dynamic Hostname (notag)
* 0000.0000.0001 R11 0000.0000.0002 R2

What is the IS-IS command to show the IS-IS database?

show isis database

IS-IS Level-1 Link State Database:
LSPID LSP Seq Num LSP Checksum LSP Holdtime ATT/P/OL
R1.00-00 * 0x00000002 0x4BD3 676 0/0/0
R1.00-01 * 0x00000002 0xF403 708 0/0/0
R1.00-02 * 0x00000003 0xF86B 643 0/0/0R2.00-00 0x00000003 0x449C 574 0/0/0

What does a single LSP contain? 3

-Adjancencies to neighboring routers/network (similar type 1 LSA)
-Intra-area and inter-area prefixes (similar to type 1,2,3 LSA's)
-External prefixes (similar to type 5/7 LSAs)

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