Is-Is Cheat Sheet

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IS-IS
P
1
ART
packetlife.net
Protocol Header
Attributes
4
8
12
16
Type
Link-State
IRPD
Packet Length
Algorithm
Dijkstra
Version/Protocol ID Extension
ID Length
Metric
Default (10)
R
R
R
PDU Type
Version
AD
115
Reserved
Maximum Area Addresses
Standard
ISO 10589
Type
Length
Protocols
IP, CLNS
Value ...
Transport
Layer 2
Authentication Plaintext, MD5
NSAP Addressing
Routing Levels
Interdomain Part
Domain-Specific Part
Level 0
Used to locate end systems
NSAP
AFI
IDI
HODSP
Level 1
Routing within an area
System ID
SEL
Condensed
Area
Level 2
Backbone between areas
Example
47
0005.80ff.f800.0000
0001
0000.0c00.1234
00
Level 3 Inter-AS routing
Interdomain Part (IDP)
Terminology
Portion of the address used in routing between autonomous
Type-Length-Value (TLV)
systems; assigned by ISO
Variable-length modular datasets
Domain-Specific Part (DSP)
Link State PDU (LSP)
Portion of the address relevant only within the local AS
Carry TLVs encompassing link state
information
Authority and Format Identifier (AFI)
Identifies the authority which dictates the format of the address
Sequence Number Packet (SNP)
Used to request and advertise LSPs; can
Initial Domain Identifier (IDI)
be complete (CSNP) or partial (PSNP)
An organization belonging to the AFI
Hello Packet
High Order DSP (HODSP)
Establishes and maintains neighbor
The area within the AS
adjacencies
System ID
Designated Intermediate System
Unique router identifier; 48 bits for Cisco devices (often taken from
A pseudonode responsible for emulating
a MAC address)
point-to-point links across a multi-access
segment
NSAP Selector (SEL)
Identifies a network layer service; always 0x00 in a NET address
Adjacency Requirements
Network Types
Interface MTUs must match
Broadcast
Point-to-Point
Levels must match
DIS Elected Yes
No
Areas must match (if level 1)
Neighbor Discovery Yes
Yes
System IDs must be unique
Hello/Dead Timers 10/30
10/30
Authentication must succeed
Troubleshooting
DIS Election
show ip route
show isis spf-log
Highest-priority interface elected
show ip protocols
debug isis spf-events
Highest SNPA (MAC/DLCI) breaks tie
show [clns|isis] neighbor
debug isis adjacencies-packets
Highest system ID breaks SNPA tie
show [clns|isis] interface
debug isis spf-statistics
Default interface priority is 64
show isis database
debug isis update-packets
Current DIS may be preempted
by Jeremy Stretch
v2.0

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