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VPLS Multicast Support

Answered Question
Sep 25th, 2006
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I want to deploy muticasr on VPLS, can you all tell me, wthether is it possible and also what are the design and implementation considerations i should have??


Brgds,


Correct Answer by swaroop.potdar about 10 years 10 months ago

There isnt anything like EoMPLS or VPLS support for multicast till now, as the PW VC are transaparent to the traffic being switched through them and the endpoints maintain the state what is to be sent on a PW.


Having said that, the forwarding decision are taken by the endpoint based on MAC table formed using the native ethernet method of flooding learning and forwarding.


Lets look at this topology;

SW1<--->SW2<-->SW3<--->SW1.



Now assume they are plain switches connected using normal ethernet ports and fibre/copper.

Now if we enable igmp snooping and start multicst traffic from SW1 to a receiver in SW2, then

first it would be flooded on interface connecting to both SW2 and SW3 from SW1.

Once the receiver state is dicovered and the outgoing interface is known as interface

connecting to SW2 the interface towards SW3 is pruned. and it will no more be flooded

across that interface for that group.


Now in VPLS these interconnecting interfaces are replaced by PW. so you have logical connection

between SW1 to SW2 and SW3. And also PE endpoints cannot maintain multicast state in relation to PW VC till now.


The working group on this VPLS draft is considering this aspect for introducing snooping or multicast state maintainence in relation ot PW VC's. till then it will be conisdered as unknwon and flooded across all the neighbors on a VPLS VFI instance.



So if you deploy Mcast on VPLS, it will be broadcasted across the connecting PW VC's,

to atleast make it scale you can thing of having a HUB-n-Spoke VPLS between the source

and destination. If you are trying to dpeloy such multicast over for a Metro-E Access clouds seperated over through MPLS cloud.


HTH-Cheers,

Swaroop

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ariela Wed, 09/27/2006 - 04:00
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Hi,


from http://www.cisco.com/en/US/products/hw/routers/ps368/products_white_paper09186a00801df1df.shtml


" VPLS is a multipoint L2 VPN technology that allows multiple sites to be connected over a simulated Ethernet broadcast domain that is supported across a provider provisioned IP/MPLS network. In other words, VPLS delivers multipoint Layer 2 connectivity over a Layer 3 network architecture. VPLS evolved as a logical extension of Ethernet over MPLS (EoMPLS), which was developed to enable point-to-point Ethernet-based L2 VPN services."


My question is: EoMPLS had multicast support?


VPLS seems to have that support:


" At a basic level, VPLS can be defined as a group of Virtual Switch Instances (VSIs) that are interconnected using EoMPLS circuits in a full mesh topology to form a single, logical bridge. In concept, a VSI is similar to the bridging function found in IEEE 802.1q bridges in that a frame is switched based upon the destination MAC and membership in a Layer 2 VPN (a virtual LAN or VLAN). If the destination address is unknown, or is a broadcast or multicast address, the frame is flooded to all ports associated with the VSI, where a port, in the context of VPLS, is an EoMPLS VC pseudowire."


But there's a problem with broadcast, that could be potentially dangerous for a multicast topology:


" The primary shortcoming of VPLS is the broadcast replication that it must perform whenever it is transmitting an Ethernet packet with either a multicast MAC address or an unknown MAC address. In both cases, the Ethernet packet must be broadcast throughout the VPLS. However, the VSI associated with a VPLS instance is a logical bridge entity that connects to all other VSIs in the VPLS using EoMPLS pseudowires. Therefore, the Ethernet packet to be broadcast must be replicated on all EoMPLS pseudowires that are associated with a particular VSI. This replication is usually not as efficient as the mechanism for transmitting broadcast traffic with Ethernet switching technology, because broadcast traffic need only be transmitted once per physical interface with Ethernet switching technology, but may need to be replicated multiple times over the same physical interface with VPLS technology. Furthermore, the amount of VPLS replication that must be performed increases exponentially as the number of end points in the VSI increases."


I'm sure a VPLS and EoMPLS guru will better explain that.


Regards

Andrea

Correct Answer
swaroop.potdar Wed, 09/27/2006 - 08:25
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There isnt anything like EoMPLS or VPLS support for multicast till now, as the PW VC are transaparent to the traffic being switched through them and the endpoints maintain the state what is to be sent on a PW.


Having said that, the forwarding decision are taken by the endpoint based on MAC table formed using the native ethernet method of flooding learning and forwarding.


Lets look at this topology;

SW1<--->SW2<-->SW3<--->SW1.



Now assume they are plain switches connected using normal ethernet ports and fibre/copper.

Now if we enable igmp snooping and start multicst traffic from SW1 to a receiver in SW2, then

first it would be flooded on interface connecting to both SW2 and SW3 from SW1.

Once the receiver state is dicovered and the outgoing interface is known as interface

connecting to SW2 the interface towards SW3 is pruned. and it will no more be flooded

across that interface for that group.


Now in VPLS these interconnecting interfaces are replaced by PW. so you have logical connection

between SW1 to SW2 and SW3. And also PE endpoints cannot maintain multicast state in relation to PW VC till now.


The working group on this VPLS draft is considering this aspect for introducing snooping or multicast state maintainence in relation ot PW VC's. till then it will be conisdered as unknwon and flooded across all the neighbors on a VPLS VFI instance.



So if you deploy Mcast on VPLS, it will be broadcasted across the connecting PW VC's,

to atleast make it scale you can thing of having a HUB-n-Spoke VPLS between the source

and destination. If you are trying to dpeloy such multicast over for a Metro-E Access clouds seperated over through MPLS cloud.


HTH-Cheers,

Swaroop

swaroop.potdar Fri, 09/29/2006 - 05:27
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  • Blue, 1500 points or more

Hows it going, did you try to test it further.


Do respond back if you have any further considerations or query.


HTH-Cheers,

Swaroop

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