Currently in Migration - Jason Edelman's Old Blog
  • Home
  • About
  • Contact

Nexus FEX "SMART" Multicast Replication

12/11/2011

1 Comment

 
The Nexus 2000 as we all know gets its intelligence from its parent switch, i.e. Nexus 7000 or 5000.  The Nexus 2000 for the most part is just a dumb device, otherwise known as a Fabric Extender (FEX).  It may be a surprise for some, but even communication between two ports on the same fabric extender goes like this: FEX Source Port – Parent Switch – FEX Destination port.  The same holds true for the Cisco UCS Fabric Interconnect (6100 and 6200 series) and the local FEX that resides in a UCS Blade Enclosure. 

After having a recent conversation with Cisco and a financial customer around how L2 multicast works between a UCS 6120 and a FEX, it actually uncovered something interesting with regards to how this multicast flows.

When looking at a multicast stream that has N destinations in the same blade enclosure (Cisco UCS B-Series), a few of us were thinking there would be N streams sent from the fabric interconnect to the actual FEX or blade enclosure.  But, when thinking about the same example from the point of view of a Nexus 5K/2K, that would be utter non-sense – it would be the most inefficient way to distribute multicast in any data center fabric design.  I think it was just the “blade” + “FEX” that was causing some confusion because the FEX is just a dumb device, right?

Well, let’s be honest, it is.  A fabric extender is nothing, nada, zilch without its parent switch, but there is *some* intelligence when it comes to multicast replication.  One stream would be sent from the parent switch to the FEX (2248, etc.) and the FEX would then replicate the packet out to all required ports, just like a L2 switch running IGMP snooping. 

Here is a Cisco slide (source: Cisco LIVE 2011) that depicts the Nexus 2000 multicast forwarding architecture – this should clear up any concern one may have around multicast in a FEX architecture.  The same holds true for UCS designs as well.

Picture
1 Comment
jiri slintak
8/21/2013 09:04:25 pm

Hello,
thx for nice update, is it same principal used for broadcast traffic so N5k just only single stream and N2k replicate into ports?

Reply



Leave a Reply.

    Author

    Jason Edelman, Founder of Network to Code, focused on training and services for emerging network technologies. CCIE 15394.  VCDX-NV 167.


    Enter your email address:

    Delivered by FeedBurner


    Top Posts

    The Future of Networking and the Network Engineer

    OpenFlow, vPath, and SDN

    Network Virtualization vs. SDN

    Nexus 7000 FAQ

    Possibilities of OpenFlow/SDN Applications 

    Loved, Hated, but Never Ignored #OpenFlow #SDN

    Software Defined Networking: Cisco Domination to Market Education

    OpenFlow, SDN, and Meraki

    CAPWAP and OpenFlow - thinking outside the box

    Introduction to OpenFlow...for Network Engineers


    Categories

    All
    1cloudroad
    2011
    2960
    40gbe
    7000
    Arista
    Aruba
    Big Switch
    Brocade
    Capwap
    Christmas
    Cisco
    Controller
    Data Center
    Dell Force10
    Embrane
    Extreme
    Fex
    Hadoop
    Hp
    Ibm
    Isr G2
    Juniper
    Limited Lifetime Warranty
    Meraki
    Multicast
    N7k
    Nexus
    Nicira
    Ons
    Opendaylight
    Openflow
    Openstack
    Presidio
    Qsfp
    Quick Facts
    Routeflow
    Sdn
    Sdn Ecosystem
    Security
    Ucs


    Archives

    May 2015
    April 2015
    February 2015
    January 2015
    December 2014
    November 2014
    October 2014
    September 2014
    August 2014
    June 2014
    May 2014
    March 2014
    February 2014
    January 2014
    December 2013
    November 2013
    October 2013
    September 2013
    August 2013
    July 2013
    June 2013
    May 2013
    April 2013
    March 2013
    February 2013
    January 2013
    December 2012
    November 2012
    October 2012
    June 2012
    May 2012
    April 2012
    March 2012
    February 2012
    January 2012
    December 2011
    November 2011


    RSS Feed


    View my profile on LinkedIn
Photo used under Creative Commons from NASA Goddard Photo and Video