Posts from ‘IP Multicast’


This week I will be running the following free online classes:

*Free for AAP Members

INE will also be offering the following free upcoming online classes:

  • CCNA R&S Overview and Preparation – Tues April 21st @ 09:00 PDT (16:00 UTC)
  • CCNP R&S Overview and Preparation – Thurs April 23rd @ 09:00 PDT (16:00 UTC)
  • CCNP R&S TSHOOT Overview and Preparation – Thurs April 30th @ 09:00 PDT (16:00 UTC)

More information on these classes can be found here.

CCIE Service Provider v4 Kickoff

This class marks the kickoff of INE’s CCIE SPv4 product line for the New CCIE Service Provider Version 4 Blueprint, which goes live May 22nd 2015!  In this class we’ll cover the v3 to v4 changes, including exam format changes and topic adds and removes, recommended readings and resources, INE’s new CCIE SPv4 hardware specification and CCIE SPv4 Workbook, and the schedule for INE’s upcoming CCIE Service Provider Version 4 Advanced Technologies Class.  Class runs tomorrow, Tuesday April 14th at 09:00 PDT (16:00 UTC), and is free to attend.  Simply sign up for an INE Members account or visit this direct link for the class.

CCIE Routing & Switching v5 Overview and Preparation

This class is an update for our previous How to pass the CCIE R&S with INE’s 4.0 Training Program write-up. This session covers in detail the recommended process of preparing for, and ultimately passing, the CCIE R&Sv5 Lab Exam. Class topics include how to develop a study plan, recommended readings and resources, how to get the most out of INE’s CCIE RSv5 Workbook & Advanced Technologies Class (ATC), an overview of our new upcoming CCIE Routing & Switching Lab Cram Session, and final strategy for the actual day of the Lab Exam. Class runs Thurs April 16th at 09:00 PDT (16:00 UTC), and is free to attend.  Simply sign up for an INE Members account or visit this direct link for the class.

Intro to IPv4 & IPv6 Multicast

This class is for engineers looking to get their feet wet in learning why and how to implement IP Multicast Routing for both IPv4 and IPv6 based networks. This one-day class will focus on IPv4 & IPv6 Multicast practical use cases, how Protocol Independent Multicast (PIM), IPv4 Internet Group Management Protocol (IGMP), & IPv6 Multicast Listener Discovery (MLD) work from a theory point of view, and implementation examples of configuring and verifying multicast routing operations on Cisco IOS based platforms. This class will also benefit candidates preparing for the CCIE RSv5 or CCIE SPv4 certifications. Class runs Friday April 17th at 09:00 PDT (16:00 UTC), and is free to attend for All Access Pass members. More information on All Access Pass subscriptions and benefits can be found here. AAP members will find the link to this class on Friday via their INE Members account, or via this direct link for the class.

I hope to see you all in class this week!


Today launches the first of many of our new INE Video Blog series.  Our first video covers the advanced design issues with running Multicast and Auto-RP over NBMA networks such as Frame-Relay Hub-and-Spoke.  Specifically this video focuses on possible solutions such as sparse-dense mode, sparse-mode with auto-rp listener, sparse-mode with a default RP placement, and PIM Join issues related to point-to-point vs multipoint interfaces and their underlying IGP protocols.
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In this short article we’ll take a look at Cisco IOS static multicast routes (mroutes) and the way they are used for RPF information selection. Multicast routing using PIM is not based on propagation of any type of multicast routes – the process that was used say, in DVMRP. Instead, router performs RPF checks based on the contents of unicast routing table, populated by regular routing protocols. The RPF checks could be classified as either data-plane or control-plane. Data-plane RPF check applies when router receives a multicast packet, to validate if the interface and upstream neighbor sending the packet match RPF information. For data-plane multicast, the packet must be received from an active PIM neighbor on the interface that is on the shortest path to the packet source IP address, or RPF check would fail. Control-plane RPF check is performed when originating/receiving control-plane messages, such as sending PIM Join or receiving MSDP SA message. For example, PIM needs to know where to send the Join message for a particular (S,G) or (*,G) tree, and this is done based on RPF lookup for the source IP or RP address. Effectively for PIM, RPF check influences the actual multicast path selection in the “reversed way”: it carves the route that PIM Join message would take and thus affects the tree construction. In both control and data-plane RPF check cases, the process is similar, and based on looking through all available RPF sources.

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I recently received an email from a student with a question about an example I did in our multicast bootcamp. After an hour into testing and drafting my email response, I realized this commonly misunderstood multicast design would make a great blog writeup! The original question is as follows:

Dear Brian

I am a customer of INE and bought the multicast bootcamp. Maybe I missed some important note, but I am confused related to the issue mentioned below. I am following the test bed you have shown in the presentation while describing the theory of sparse mode (Day 1 – Part 6) in which you have explained the RP Register, Join and SPT-Join.

Suppose the two trees are established, and traffic is flowing from the source to RP, and then RP to receiver. Also suppose that SPT-Join is disabled (e.g. threshold is infinity), and traffic always follows the shared trees.

Suppose that the multicast traffic flow is initiated from the source to the RP as follows:

R2 –> R4 –> R3 (RP)

Then traffic flows from the RP to receiver:

R3 –> R4 –>R5

When multicast traffic is coming from the RP on R4, will RPF check fail? I assume so, since multicast traffic is entering the interface in which RPF will be failed. Is there any other rule to follow if traffic is coming from RP?

Best Regards


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After working with the December 2010 London Bootcamp on Multicast for the better part of Day 4 in our 12-day bootcamp, I returned to the hotel to find the following post on my Facebook page – “Multicast is EVIL!”

Why do so many students feel this way about this particular technology? I think one of the biggest challenges is that troubleshooting Multicast definitely reminds us of just what an “art” solving network issues can become. And speaking of troubleshooting, in the Version 4 Routing and Switching exam, we may have to contend with fixing problems beyond the scope of our own “self-induced” variety. This is, of course, thanks to the initial 2 hour Troubleshooting section which may indeed include Multicast-related Trouble Tickets.

Your very best defense against any issues in the lab exam regarding this technology – the new 3-Day Multicast technology bootcamp. Also, be sure to enjoy the latest free vSeminar from Brian McGahan – Troubleshooting IP Multicast Routing.

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INE is proud to announce the release of our Multicast Class-on-Demand! Taught by myself, this 15-hour Class-on-Demand series covers IPv4 and IPv6 Multicast Routing on Cisco IOS, including both technology lectures and hands-on CLI examples. More information on the Multicast Class-on-Demand can be found here.

To celebrate the release of this new Class-on-Demand, I will be running a free vSeminar on Troubleshooting IP Multicast Routing this Thursday, October 14th, at 10:00 am PDT (17:00 GMT). This free seminar will run about an hour long, and will cover CLI examples of how to troubleshoot common IP Multicast problems, including RPF failure and the use of static multicast routes & mtrace. For those unable to attend, this vSeminar will be available in recorded Class-on-Demand format at a later date. The url to attend is

Click here to register for notifications about new upcoming vSeminars.

Hope to see you there!

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When we ask students “what are your weakest areas” or “what are your biggest areas of concern” for the CCIE Lab Exam, we typically always here non-core topics like Multicast, Security, QoS, BGP, etc. As such, INE has responded with a series of bootcamps focused on these disciplines.

The IPv4/IPv6 Multicast 3-Day live, online bootcamp, and the associated Class On-Demand version seeks to address the often confounding subject of Multicast. Detailed coverage of Multicast topics for the following certifications is provided:

Cisco Certified Network Professional (CCNP)

Cisco Certified Design Associate (CCDA)

Cisco Certified Design Professional (CCDP)

Cisco Certified Design Expert (CCDE)

Cisco Certified Internetwork Expert Routing & Switching (CCIE R&S)

Cisco Certified Internetwork Expert Service Provider (CCIE Service Provider)

Cisco Certified Internetwork Expert Security (CCIE Security)

To purchase the live and on-demand versions of the course for just an amazing $295 – just click here. The live course runs 11 AM to 6 PM EST US on September 29,30, and October 1.

The preliminary course outline is as follows:

  • Module 1 Introduction to Multicast

Lesson 1 The Need for Multicast

Lesson 2 Multicast Traffic Characteristics and Behavior

Lesson 3 Multicast Addressing

Lesson 4 IGMP

Lesson 5 Protocol Independent Multicast

  • Module 2 IGMP

Lesson 1 IGMP Version 1

Lesson 2 IGMP Version 2

Lesson 3 IGMP Version 3

Lesson 4 CGMP

Lesson 5 IGMP Snooping

Lesson 6 IGMP Optimization

Lesson 7 IGMP Security

Lesson 8 Advanced IGMP Mechanisms

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This publication illustrates some common techniques for troubleshooting multicast issues in IP networks. Common problems and their causes are discussed, troubleshooting techniques demonstrated. PIM Sparse mode is used for most of the examples, due to the fact that this is the most complicated mode of multicast signaling. The suggested troubleshooting approach separates control plane from data-plane troubleshooting and heavily relies on the mroute command for the control-plane verification. This publication requires solid understanding of intra-domain multicast routing technologies.

Common Reasons for Multicast Problems

In short, one common reason for all issues with multicast routing is the PIM and logical/physical topology incongruence. Ideally, multicast should be deployed in a single IGP domain with PIM enabled on all links running the IGP with all links preferably being point-to-point or broadcast multiple-access. If you have multicast running across the domain that has multiple IGPs, or you don not have PIM enabled on all links or finally you have NBMA links in the topology – you have open possibilities for a problem. Unfortunately, the “problem” conditions just described are very common in the CCIE lab exam environment.

The most common type of multicast issue is the RPF Failure. RPF checks are used both at the control and data plane of multicast routing. Control plane involves PIM signaling – some PIM messages are subject to RPF checks. For example, PIM (*,G) Joins are sent toward the shortest path to RP. Next, the BSR/RP address in the BSR messages is subject to RPF check as well. Notice that this logic does not apply to PIM Register messages – the unicast register packet may arrive on any interface. However, RPF check is performed on the encapsulated multicast source to construct the SPT toward the multicast source.

Data plane RPF checks are performed every time a multicast data packet is received for forwarding. The source IP address in the packet should be reachable via the receiving interface, or the packet is going to be dropped. Theoretically, with PIM Sparse-Mode RPF checks at the control plane level should preclude and eliminate the data-plane RPF failures, but data-plane RPF failures are common during the moments of IGP re-convergence and on multipoint non-broadcast interfaces.

PIM Dense Mode is different from SM in the sense that data-plane operations preclude control-plane signaling. One typical “irresolvable” RPF problem with PIM Dense mode is known as “split-horizon” forwarding, where packet received on one interface, should be forwarded back out of the same interface in the hub-and-spoke topology. The same problem may occur with PIM Sparse mode, but this type of signaling allows for treating the NBMA interface as a collection of point-to-point links by the virtue of PIM NBMA mode.
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A pretty important topic that is very easy to overlook when studying multicast is the PIM Assert Mechanism.  After working with the TechEdit Team in the IEOC it is obvious that more than just a handful of students are confused about what this mechanism does and how it works. In this blog post (the first of many dedicated to multicasting), we will examine the PIM Assert mechanism and put this topic behind us in our preparation in mastering multicast.

In Figure 1, R1 and R4 have a route to the source (the multicast source), and share a multi-access connection to R6. R6’s FastEthernet0/0 interface has joined the multicast group

Figure 1

Figure 1

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Hello everyone!

I am updating Practice Exam 2 (In Progress) for the CCIE Written Exam Bootcamp in your Members’s Site. I will be adding questions over the next couple of weeks. Currently, you will find some new Multicast Addressing/IGMP/MLD questions in there for your entertainment.

I am focusing on Practice Exam 2 right now for two main reasons. 1) It is allowing me to address some deficiencies with Practice Exam 1 and the lectures, and 2) More and more students are using this bootcamp as a prep tool for the dreaded Core Knowledge section.

Let us examine one of the new questions and walk through my solution logic.

Q. How does a router respond after receiving an IGMP Leave Group message?

a. The router does nothing

b. The router responds with a Membership Report

c. The router responds with a Group Specific Query

d. The router responds with a General Query

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