Server to Server Multicast Query

[Muhammad Anser Khan]

Dear All,

I have a below query related to Basic (Server to Server) multicast within the same subnet and vlan but connected to two different switches.

Below is the scenario:

In N5K = Acting as a layer 2 and "ip igmp snooping" is enabled

In Dist_CAT65K= Acting as a layer 2 for Vlan1 and "no ip igmp snooping" configured globally (disabled)

In Core_CAT65K= Acting as a layer 3 for Vlan1 (SVI) and "no ip igmp snooping" configured globally (disabled)

Server-1 ---> N5K-1 ---> Dist_CAT65K-1 ---> "Core_CAT65K-1 <<====>> Core_CAT65K-2" <--- Dist_CAT65K-2 <---- N5K-2 <----- Server-2 

Kindly suggest what is the best way to enable multicast end to end.

I have one solution to enable 'pim' under SVI in the core switch:

Core_CAT65K:
!
interface Vlan1
ip address 1.1.1.1 255.255.255.0
ip pim sparse-dense-mode
end
!

To enable 'pim,' Do we need to enable "ip multicast-rouing" in Core_CAT65K?

Do we need to enable "ip igmp snooping" in  Core_CAT65K?

Is it better to enable "ip igmp snooping" in Dist_CAT65K? What If we not enable IGMP Snooping on Dist_CAT65K?

Or Multicast will still work without doing anything because IGMP is disabled on Core_CAT65K &  Dist_CAT65K and Multicast packets will be treated as Broadcast in Core_CAT65K?

What is the best way?

Regards,

Anser

[Jon Marshall · Accepted solution]

Anser

In the same vlan you do not need to enable multicast routing and you do not need to configure PIM on the L3 SVI. You are correct when you say if IGMP snooping is disabled the multicast packets are simply flooded to all ports except the one it was received on.

If you want to set it up so that only the ports that need the multicast stream receive it then -

1) enable IGMP snooping on all switches

2) on one of the switches enable the IGMP snooping querier function. This is so IGMP queries are made within the vlan which are needed for IGMP snooping to listen to.  Note, if you enabled PIM on an interface IGMP queries would automatically be made but when there is no need for PIM you can use the querier function instead -

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/snooigmp.html#wp1119663

Jon

[Joseph W. Doherty]

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Posting

If you have a multicast capable router, my suggestion would be to use it for the IGMP querier - this to better position your network if you eventually do find a need to do multicast routing.

[Muhammad Anser Khan]

Hi Jon,

Thank for your useful response. I want to clarify some concepts. What will the result for the following scenarios:

1- Enable IGMP Snooping & IGMP Snooping Querier on Core_C65K (Inside SVI):

   In this scenario, IGMP snooping will remain disabled globally but enable under VLAN Interface (SVI) in Core_C65K

and IGMP snooping also disabled on Dist_C65K and only Nexus5K have IGMP snooping enabled but no IGMP Snooping Querier on N5K. Will this scenario work?

2- Enable IGMP Snooping Querier on Nexus5K (Inside VLAN):

   In this scenario, IGMP Snooping will remain disabled in Core_C65K & Dist_C65K globally & diabled under Vlan or SVI as well.

3- Enable IGMP Snooping on all the switches (N5K, Dist_C65K & Core_C65K) and configure IGMP Snooping Querier in SVI on Core_C65K:

   Is this scenario recommended by you?

4- What is the current multicast traffic status between N5Ks?

    In this scenario, IGMP Snooping is enabled in N5K only (No querier) but disabled in Dist_C65K & Core_C65K.

Appreciate your response.

Regards,

Anser

[Jon Marshall]

Anser

1) The querier function only needs to be enabled on one switch for the vlan so you don't need to configure it on both the 6500 and the Nexus switch.

If you don't enable IGMP snooping on  a switch then the switch has no way of mapping ports to a multicast stream so it will be flooded to all ports on that switch (other than the one it was received on).

2) Similiar answer to 1) just different switch using IGMP snooping querier. IGMP snooping and IGMP snooping querier are different functions.

3) Yes, this is the recommended solution because then the multicast stream will only be sent out to the ports that requested the stream. This is the most efficent scenario in terms of multicast traffic.

4) Not sure i understand. If there is no querier and you do not have PIM enabled (which you don't because the mutlicast is within the same vlan) then all switches would flood the multicast packets.

Jon

[Muhammad Anser Khan]

Hi Jon,

Thanks again. Just to clarify, What is the impact If I disable IGMP Snooping globally and enable on the specific SVI & vlan? e.g

Core_C65K:

Config# no ip igmp snooping

Config# no ip igmp snooping querier

Config# inter vlan 1

Config-if)#ip igmp snooping

Config-if)#ip igmp snooping querier

Dist_C65K:

Config# no ip igmp snooping

Config# vlan configuration 1

Config-vlan# ip igmp snooping

N5K:

Enable (ip igmp snooping) globally & Vlan as well.

Can I get the optimal multicast traffic between the same VLAN with the above configuration?

Regards,

Anser

[Jon Marshall]

Anser

You should only need to enable IGMP snooping within the specific vlan if the switch supports it. Because you are not routing the multicast traffic then you do not need to enable IGMP snooping globally.

Note though that IGMP snooping is a hardware based feature so even if you did enable it globally you should not see any significant increase in CPU/memory use. In fact on most switches it is enabled globally by default.

Jon

[Muhammad Anser Khan]

Hi Jon,

Thanks.

I have a requirement to control the multicast traffic within the same vlan.

I have couple of server in the same vlan & subnet and they want to communicate with specific servers e.g.

VLAN 10 (Subnet 10.1.1.0/24)

The multicast stream between the Server IPs: 10.1.1.1 to 10.1.1.4 donot interfere/reach with Servers IPs: 10.1.1.10 to 10.1.1.15.

What are the possible ways to control multicast within the VLAN?

Who is responsible to control multicast groups? Network or Application?

Regards,

Anser

[Jon Marshall]

Anser

Then you should use IGMP snooping together with the IGMP snooping querier so only those servers receive the stream. The other servers will not receive the stream.

That said though, if you want to actually stop certain servers from actually requesting and receiving the stream you would need to use acls on the actual ports connected to those servers. But they would still only receive the stream if they requested it ie. if you know these servers will never request the stream and simply want to make sure the stream is not flooded to them IGMP snooping + querier is the way to go.

The network team are responsible for controlling multicast on the network equipment. The actual application setup in terms of TTL settings etc. is usually down to the server team.

Jon

[Muhammad Anser Khan]

Hi Jon,

I will implement the below scenario as discussed earlier:

3) Yes, this is the recommended solution because then the multicast stream will only be sent out to the ports that requested the stream. This is the most efficent scenario in terms of multicast traffic.

I hope there will be no interference from the network infrastructure.

Regards,

Anser