Showing results for 
Search instead for 
Did you mean: 

Multicasting - Windows Deployment Services


Hello everyone,

We have recently implemented Windows Deployment Services on our local network, but everytime we do a multicast image deployment the network get flooded to point of total saturation.

We have Netgear switches and a Cisco 2800 series router. IGMP Snooping has been enabled on all Switches, however, we are unsure on how to implement multicasting on the router.

The whole network is flat - no VLANs over than the default VLAN1. We only want multicasting to work within our local network and does not need to go out the other side of the router as that is the connection to the internet.

We would be grateful if anyone could give us some ideas on how to get the Cisco router configured properly to enable multicasting to not flood the network. It seems that even if we were to image 4 PCs using multicast this is enough to completely get the network flooded.

Also, am I right in thinking that IGMP needs to be enabled on all of the Switches?

This issue is starting to become urgent.

Thanks for your help, it is much appreciated!

Jonathan Worth.


Ton V Engelen


i dont have any experience with both Netgear and the 2800 series, so i m afraid i m not of much help.

But i ll try and give a description of what we did as we have this working with multicast. (w/ 6500 and 3750 switches)

At the 6500 switch (l3) i enabled

- ip multicast routing (global)

- ip pim sparse mode at l3 interfaces level (or else dense or sparse-dense mode at l3 interface command level)

- i use ip sparse mode, so i defined 2 RP's.

at the 3750 switch (l2)

- ip igmp snooping

I use the following commands to check

at the switch

- show ip igmp snooping (is it enabled? )

at the router

- show ip igmp membership (How many mc sessions are there, what are they, is "my" multicast sesion there? How many members has it)

I also use wireshark at the server and at a client (do i see multicast packets, and what is the mc address)

show ip igmp membership | i

This outputs hosts which are member of that session.

I know that much of the success depends on how the W servers are configured for distribution with multicast, so make sure the W servers are configured correctly or have it double checked.

(Btw, to do a quick test, install wireshark on a client and check if you see any multicast traffic coming in from the server.)

Good luck.


I'm not sure why I need router to deploy computers using multicast if server and clients are in the same network. Can someone please explain this to me?

I would like to multicast deploy computers using WDS with only my server, clients and Catalyst 3750 switch as my infrastructure. If this is not possible, can someone please explain how should server, router, switch and clients be connected (physical connections, what subnets should I use and where, how should a router and switch be configured)? I'm asking just for test environment specifications, nothing more complex.

Thank you!

Best wishes,


Peter Paluch
Hall of Fame Cisco Employee Hall of Fame Cisco Employee
Hall of Fame Cisco Employee


For a multicast in a single network, no router is necessary as there is no routing involved. However, there is a more mundane thing to watch for: Cisco switches use a technique called IGMP Snooping to dynamically find out through which ports should a received multicast stream be replicated. This is used to optimize the multicast stream delivery within a switched network because otherwise, the stream would be delivered to all stations just like a broadcast. This IGMP Snooping mechanism is based on intercepting the IGMP Join (or better called, Membership Report) message sent by subscribed stations. The gotcha here is that after the station joins a group, it sends a single IGMP Join message but after that, it will only send the IGMP Join again when it receives an IGMP Membership Query message. These Queries are usually sent by multicast-enabled router and are vital to keep stations periodically announcing their subscription to selected groups.

Now, in a network without a multicast-enabled router, there is nobody to send these queries. That would cause the entries on switches created by IGMP Snooping to expire soon, and the multicast delivery would be stopped.

That is why Catalyst switches actually implement a so-called IGMP Snooping Querier functionality - the capability of the switch itself to send IGMP Query packets to periodically refresh the subscription status of the connected stations, even though the switch is not going to perform true multicast routing. So with IGMP Snooping Querier, you do not need any multicast-enabled router in your network at all - if you're fine with multicasting being confined to a single VLAN only.

The IGMP Snooping Querier must be activated manually. In order for it to work correctly, you should configure a SVI for the VLAN you want to use the multicast in at your 3750, assign it an appropriate IP address, and then enter the following command in the global config mode:

ip igmp snooping querier

That should do the necessary trick.

Best regards,



This sounds great, thank you!

I will try it.

Best wishes,



can you please check if this looks OK to you? It is configured on Cisco SG300-52 switch (I have entered "ip igmp snooping vlan 3 querier", because I will be deploying computers on VLAN 3 - server and clients are on this VLAN):

sw-01#show ip igmp snooping interface 3

IGMP Snooping is globaly disabled
IGMP Snooping admin: Disabled
IGMP Snooping oper mode: Disabled
Routers IGMP version: 3
Groups that are in IGMP version 2 compatibility mode:
Groups that are in IGMP version 1 compatibility mode:
IGMP snooping querier admin: enabled
IGMP snooping querier oper: disabled
IGMP snooping querier address admin:
IGMP snooping querier address oper:
IGMP snooping querier admin version: 2
IGMP snooping robustness: admin 2  oper 2
IGMP snooping query interval: admin 125 sec oper 125 sec
IGMP snooping query maximum response: admin 10 sec oper 10 sec
IGMP snooping last member query counter: admin 2  oper 2
IGMP snooping last member query interval: admin 1000 msec oper 1000 msec
IGMP snooping last immediate leave:  disable
Automatic learning of multicast router ports is enabled

Thank you!

Best wishes,


Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: