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CCNP Tutorial For The BSCI Exam:

An Illustrated Look At IGMP Versions 2 and 3

Chris Bryant, CCIE #12933

 

Vital Reading And Watching For All Cisco Certification Candidates:

The July 2010 CCNP Changes (And How To Beat Them!)

 

In the previous section of this CCNP multicasting tutorial, we saw how and why multicast trees are built and how IGMP version 1 operates.

We also saw that IGMP v1 isn't particularly efficient! Thankfully, we have two other versions of IGMP to use in today's networks - and on the BSCI exam!

We'll take an illustrated look at IGMP versions 2 and 3 right after this brief yet important note - and I look forward to continuing to help you earn your CCNP!

Earn Your CCNP With The Personal Guarantee Of Chris Bryant, CCIE #12933:

“I GUARANTEE You'll Pass The Current CCNP Exams - BSCI, ONT, ISCW, and BCMSN - Before The July 31, 2010 Cutoff Date With My CCNP Study Packages ...

... And If You Don't Pass FOR ANY REASON Before That Time, I'll Give You a 100% Free CCNP Study Package Download For The New Exam Track!"

You Also Get A FREE CCNA Security Study Package With The Purchase Of Any CCNP Study Package!

CCNP BSCI Study PackageCCNP Certification Exam Study Bundle

A major difference between IGMP v1 and v2 is that IGMPv2 hosts that wish to leave a group do not just stop sending Membership Reports, and there's no three-minute wait to have the membership age out. 

Instead, IGMPv2 hosts send a Leave Group message to the reserved multicast address 224.0.0.2, the "all routers on this segment" address. 

IGMPv2 Leave Group

 

In return, the Querier will send a group-specific query, which will be seen by all hosts on the segment.  This query specifically asks all hosts on the segment if they would like to receive multicast traffic destined for the group the initial host left. 

If another host wants to continue to receive that traffic, that host must send a Membership Report back to the Querier.

IGMP v2 Group Specific Query

If the Querier sends that group-specific query and gets no response, the Querier will stop forwarding multicast traffic for that group onto that segment.  

Another major difference between IGMPv1 and v2 is that there is a one-step way to make a certain IGMPv2 router become the Querier, and that's to make sure it has the lowest IP address on the shared segment.

As you'd expect, there are some issues that arise when you've got some hosts on a segment running IGMPv1 and others running IGMPv2, or one router running IGMPv1 and another router running IGMPv2. 

The possible scenarios are beyond the scope of the BSCI exam, but for those of you who'd like to learn more about the interoperability of the IGMP versions (and especially if you'd like to be a CCIE one day), get a copy of RFC 2236 off the Internet and start reading!

IGMP Version 3 is also now available on many Cisco devices.  The major improvement in IGMPv3 is source filtering , meaning that the host joining a multicast group not only indicates the group it wants to join, but also chooses the source of the multicast traffic.

Multicast group members sent IGMP v3 messages to 224.0.0.22.

When a host makes that choice regarding the source of the multicast stream, it can take one of two forms:

"I will accept multicast traffic from < source x > "

"I will accept multicast traffic from any source except <source x> "

If you'd like to do some additional reading on any IGMP version, here are the RFC numbers:

IGMP v1:  RFC 1112

IGMP v2:  RFC 2236

IGMP v3:  RFC 3376

Now that the hosts are using IGMP to join the desired multicast group, we've got to get that traffic to them. For that, we'll use PIM - Protocol Independent Multicast. 

There are three modes of PIM you must be fluent with to pass the BSCI exam, as well as two different PIM versions.  You'll see all these modes and versions in production networks as well, so it's vital to understand the concepts of all of them. 

We'll take a look at those in the next installment of this CCNP Multicasting tutorial series, coming the week of March 22, 2010. See you then!

Bookmark the BSCI Exam Resource Page and visit every day in March and April for new CCNP study material - and watch the Bulldog Blog, too!

 

Earn Your CCNP With The Personal Guarantee Of Chris Bryant, CCIE #12933:

“I GUARANTEE You'll Pass The Current CCNP Exams - BSCI, ONT, ISCW, and BCMSN - Before The July 31, 2010 Cutoff Date With My CCNP Study Packages ...

... And If You Don't Pass FOR ANY REASON Before That Time, I'll Give You a 100% Free CCNP Study Package Download For The New Exam Track!"

You Also Get A FREE CCNA Security Study Package With The Purchase Of Any CCNP Study Package!

CCNP BSCI Study PackageCCNP Certification Exam Study Bundle

 

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