Learn ISIS for IPv4 and IPv6

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  • Lectures 11
  • Length 3 hours
  • Skill Level All Levels
  • Languages English
  • Includes Lifetime access
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About This Course

Published 12/2013 English

Course Description

In recent years, the IS-IS routing protocol has become increasingly popular, with widespread usage among Service Providers a part from OSPF.

Many Cisco Engineers are good with routing protocols ( like OSPF, EIGRP, RIPv2)

ISIS is the protocol majorly used inside Service providers Networks apart from OSPF.

This course will be very handy for anyone who want to master ISIS from basics.

ISIS for IPV4/IPV6 already part of Cisco ( CCNA,CCNP,CCIE ) service Provider Track and even added to new CCIE RS version 5 .

What are the requirements?

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

What am I going to get from this course?

  • Master ISIS from Basics

Who is the target audience?

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

What you get with this course?

Not for you? No problem.
30 day money back guarantee.

Forever yours.
Lifetime access.

Learn on the go.
Desktop, iOS and Android.

Get rewarded.
Certificate of completion.


Section 1: ISIS

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


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


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


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)


oExample : 49.0001.0000.0000.0007.00

Section 2: ISIS lab Verfication


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


·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.


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


·To change metric (default is 10)

oRouter(config-if)# isis metric

Section 3: Advance ISIS


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

·Configure authentication between thelink R5– R6 using MD5 password ccie123


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 to its L1 routers (R3, R4)

oR2 should advertise the L2 prefix 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.


Here I said Spanning-tree for SPF ( but it is shortest path first for ISIS ) ..


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 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


    ·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

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Instructor Biography

Senior Technical Instructor/Network Consultant

Sikandar Shaik, a dual CCIE (RS/SP# 35012), is a highly experienced and extremely driven senior technical instructor and network consultant. He has been training networking courses for more than 10 years, teaching on a wide range of topics including Routing and Switching, Service Provider and Security (CCNA to CCIE). In addition, he has been developing and updating the content for these courses. He has assisted many engineers in passing out the lab examinations and securing certifications.

Sikandar Shaik is highly skilled at designing, planning, coordinating, maintaining, troubleshooting and implementing changes to various aspects of multi-scaled, multi-platform, multi-protocol complex networks as well as course development and instruction for a technical workforce in a varied networking environment. His experience includes responsibilities ranging from operating and maintaining PC's and peripherals to network control programs for multi-faceted data communication networks in LAN, MAN and WAN environments.

Sikandar Shaik has delivered instructor led trainings in several states in India as well as in abroad in countries like China, Kenya and UAE. He has also worked as a Freelance Cisco Certified Instructor globally for Corporate Major Clients.

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