Learn ISIS for IPv4 and IPv6

Name: Learn ISIS for IPv4 and IPv6
Rating: 4.5 (363 reviews)

from Basic to Advance level.

Created bySikandar Shaik, Shaik Gouse Moinuddin

Last updated 12/2013

English

What you'll learn

Master ISIS from Basics

Course content

3 sections • 11 lectures • 2h 51m total length

introduction to ISIS6:25
ISIS features

·Open standard (OSI)

oFirst developed by DEC and It was standardized by theISOin 1992 communication between network devices which are termed Intermediate Systems by the ISO.

·Link-state routing protocol

·Classless

oFLSM, VLSM and Manual summary

·Work on SPF or Dijkstra algorithm

·Incremental / trigger updates

·Updates are send as unicast /multicast (Layer 2)

·Metric= default (Cisco)

·Administrative distance = 115

·It is used by large ISP

·Protocol independent i.e. Support IP, IPX, Apple Talk
Understanding Levels in ISIS16:45
IS-IS Levels

·ISIS has a 2 layer hierarchy

oLevel-2 (the backbone)

oLevel-1 (the areas)

·IS-IS support three type of router levels

1.Level-1 (L1) router (intra-area routing)

2.Level-2 (L2) router (inter-area routing)

3.Level-1-2 (L1L2) router (intra and inter-area routing)

·Manually Need to define IS-type

·Default is level 1/Level 2
understanding NSAP address in ISIS14:24
NSAP Address (Network Service Access Point)

·The simplest NSAP format used by most companies running IS-IS as their IGP is as follows:

·AFI set to 49

oReserved for private use.

·Area ID

oMust be at least one byte.

·SystemID: Defines an ES or IS in an area; Cisco implements

§a fixed length of 6 octets for the SystemID

·NSEL ( NSAP selector)

oAlways set to 00 for a ISIS in router.

·NSAP with NSEL 00 is also called as NET

oNET: Network Entity Title.

o Is the address of the network entity itself

o A NET is an NSAP where n-selector is 0 (common practice)

oA NET implies the routing layer of the IS itself (no transport layer)

o ISs (routers) do not have any transport layer (selector=0)

·Examples:

oExample : 49.0001.0000.0000.0007.00

LAB : Basic ISIS lab22:52
LAB: ISIS:

Configure ISIS routing for IPV4 and IPV6 as per the diagram

·Routers R1-R3–R4 should be in the same area 49.0134

·Use NET addresses in the format 49.0134.0000.0000.000X.00, where X is the router Numbers for routers R1-R3–R4

·Advertise the connected and Loopback interfaces of all the routers

·Enable Ipv6 unicast routing on all routers
ISIS DIS (Designated Intermediate System)12:55
·Unlike ospf, The ISIS DIS allows preemption,

· The default interface priority is 64 and the device with the highest SNPA (Layer2 identifier) becomes the DIS.

· If the SNPA addresses are the same then the system-id is the tie breaker.

·The DIS can be identified with either the show clns is-neighboror show isis neighbor. The device listed under the Circuit-Id field is the DIS.
LAB : Changing ISIS Levels30:58
IS-IS Levels

·ISIS has a 2 layer hierarchy

oLevel-2 (the backbone)

oLevel-1 (the areas)

·IS-IS support three type of router levels

1.Level-1 (L1) router (intra-area routing)

2.Level-2 (L2) router (inter-area routing)

3.Level-1-2 (L1L2) router (intra and inter-area routing)

·Manually Need to define IS-type

·Default is level 1/Level 2
ISIS Metrics8:33
·To change metric (default is 10)

oRouter(config-if)# isis metric

ISIS Authentication8:17
TASK

·Configure authentication between the link R3 – R4 using clear text password cisco123

·Configure authentication between thelink R5– R6 using MD5 password ccie123
ISIS Route leaking17:59
IS-IS Route Leaking for IPV4

·Configure IS-IS Route Leaking from Level 2 to Level 1 on the L1/L2 routers as follows:

oR1 should advertise the L2 prefix 6.6.6.6/32 to its L1 routers (R3, R4)

oR2 should advertise the L2 prefix 4.4.4.4/32 to its L1 routers (R5, R6)

By default R4/R3 will receive a default route for all the routes coming from different area ( AREA 49.0256) from the nearest L1/L2 router (R1)

in order to allow some of the specific routes to get from nearest L1/L2 router ( R1) to all the inside L1 routers (R3/R4) generally called as route leaking feature.
ISIS single Multi topology23:43
Here I said Spanning-tree for SPF ( but it is shortest path first for ISIS ) ..

ISIS SINGLE AND MULTITOPOLOGY

ISIS supports routing for both IPv6 and IPv4. There are new TLVs which are encoded inside the ISIS to support IPv6 addressing. IPv6 routing can be configured as either Multi-topology or Single-topology

Single Topology IS-IS

·Single Topology IS-IS is used when multiple protocol stacks, such as IPv4 and IPv6, are configured in an identical 1:1 basis on all interfaces in the topology.

·Single topology has the following characteristics –

Shares path calculation with IPv4 routing Table. Only one SPF calculation.

It requires 1:1 correlation of IPv4 and IPv6 interfaces i.e Ipv4 and IPv6 interfaces should be same.

·Simplifying database single calculation and protocol overhead as multiple protocol stacks (IPv4 and IPv6) configured in an identical 1:1 basis.

·In other words, for single topology IS-IS to work, each interface that runs IPv4 must also run IPv6, and each interface that runs IPv6 must also run IPv4.

·This is one of the design advantages of IS-IS over OSPF, as OSPFv2 and OSPFv3 are unrelated protocols used to route IPv4 and IPv6 respectively, while IS-IS can route both with a single calculation, arguably resulting in a more efficient design.

·By default :Regular IOS --> IS-IS instances run in Single Topology modeIOS XR --> ISIS instances run in Multiple Topology mode

Multi Topology IS-IS

In Multi Topology IS-IS, separate protocol stacks maintain separate database structures and use separate SPF runs, which means that one topology is independent of another.

However enabling multi-topology mode will have following effect

·Independent path calculation from IPv4 routing table. Separate SPF calculation.

·IPv4 and IPv6 configuration are completely different i.e IPv4 & IPv6 interfaces can be asymmetric.

Multi -Topology IS-IS is most useful in practical IPv4 to IPv6 migration scenarios, where IPv6 is slowly introduced to the already existing IPv4 core. During migration the IPv4 and IPv6 topologies are kept separate from a database calculation point of view inside of IS-IS. Once the migration is complete and IPv4 and IPv6 run on a 1:1 basis with each other, Single Topology IS-IS can be enabled, which means that both IPv4 and IPv6 topology share the same database and SPF run.

Note that this design is only possible if IPv4 runs on all interfaces that IPv6 runs on and vice-versa, otherwise database inconsistencies can occur which can result in loss of reachability in the network
ISIS Trouble shooting ISIS8:30
ISIS troubleshooting

·Sh isis neighbor

·sh run part router isis

·sh run int ---

=====================

·sh ip route isis

·sh ipv6 route isis

=======================ISIS issues

·net id is correct according to quetion

·ip router isis /ipv6 router isis missing under interface

·isis protocol shutdown under interface

int g0/0.10

isis protocol shutdown

end

·level mismatch ( router mode/interface mode)

·network type under interface

·In case of the below, routes will not be exchanged but still forms neighbors

·metric-style mismatch

·topology mismatch

Requirements

Basic CCNA, CCNP Routing & switching Knowledge
using Gns3 Software for simulating Labs

Description

Course Description – IS-IS Routing Protocol (Beginner to Advanced)

In recent years, the IS-IS (Intermediate System to Intermediate System) routing protocol has gained significant popularity, especially within large Service Provider networks. While many engineers are already familiar with OSPF, EIGRP, and RIP, IS-IS offers unique advantages in scalability, stability, and operational simplicity, making it a preferred choice for carrier-grade environments.

IS-IS is widely deployed inside Service Provider backbones and is commonly used as the IGP in MPLS, IPv4, and IPv6 networks. Unlike OSPF, IS-IS was originally designed for CLNS but has evolved to support modern IP networks with exceptional robustness. As a result, mastering IS-IS has become an essential skill for engineers working in Service Provider, Data Center, and Multi-Vendor environments.

This course is ideal for anyone who wants to learn IS-IS from the ground up. It covers core concepts, packet structure, adjacency formation, LSP flooding, SPF calculation, multi-level design, authentication, and advanced deployment scenarios. All lessons are explained in a clear and practical manner with real lab configurations.

IS-IS for IPv4 and IPv6 is already part of Cisco’s CCNA, CCNP Service Provider, and CCIE Service Provider blueprints, and has also been added to the new CCIE Routing and Switching v5 curriculum. This makes IS-IS not only valuable for real-world operations but also essential for engineers preparing for professional and expert-level Cisco exams.

By the end of this course, you will have a strong understanding of IS-IS concepts, configuration, and troubleshooting techniques that apply directly to production networks and certification preparation.

Who this course is for:

candidate preparing for Cisco Service Provider Track ( CCNA to CCIE) any
Candidates preparing for new CCIE RS version 5

Learn ISIS for IPv4 and IPv6

What you'll learn

Explore related topics

Course content

ISIS3 lectures • 38min

ISIS lab Verfication4 lectures • 1hr 15min

Advance ISIS4 lectures • 58min

Requirements

Description

Who this course is for: