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Community Member

Multicast Problems Between VLANs on 3750

Multicast Nightmare

Hello, can someone please help me, I have been tearing my hair out with this problem for the last few days without success.

I have a 3750 with IP Services Image. On Monday I will have a phone system on VLAN7 My Voice VLAN that will send multicast traffic that needs to be recevied by an App on some PCs on VLAN3. The 3750 is routing between the VLANs.

As the system is not here I have been testing multicast using VLC which can send and receive from Multicast addresses. Although I can send and receive multicast on the same VLAN as I would expect I cannot get it to work across VLANs using PIM.

I am now totally confused about how it should work. The switch by default has IGMP snooping enabled.

My first question relates to how it should work with just one VLAN. The thing is I dont want that multicast stream broadcast out every port on the switch in the same VLAN as the sender, as the devices on that VLAN do not want to receive the stream, but that is what appears to be happening. A test device on the same VLAN as the stream sender that is not interested in the stream is receiving it, I can see this via tcpdump.

But when I look on the switch it seems to know about where to send the stream...

wd-swh01#sh ip igmp snooping groups

Vlan Group Type Version Port List

-----------------------------------------------------------------------

7 224.1.2.3 igmp v2 Gi1/0/47

7 239.255.255.250 igmp v2 Gi1/0/48

224.1.2.3 is the stream in question. But I am seeing it on Gi7/0/2 where my tcpdump is running.

Also nothing is recorded in this output:

wd-swh01#sh mac address-table multicast

Vlan Mac Address Type Ports

---- ----------- ---- -----

Is that expected? should that not show the mutlicast address associated to various ports?

Now moving on to try to get the stream to route between VLANs I have enabled pim

Now if move port Gi1/0/47 into VLAN 3, get an IP in the new VLAN, and try to receive the stream from there I cannot.

Please see attaced config and show outputs.

I have tried completely disabling IGMP snooping on the switch to see if that was the problem but it has not helped.

I have learnt about multicast but never used it before so I dont know what to look for.

I have searched many documents without success and I would really appreicate any assistance that anyone can give me.

Thanks is advance

Steve

4 REPLIES
Cisco Employee

Re: Multicast Problems Between VLANs on 3750

Steve,

For the multicast test between the two vlans, did you set the TTL to something greater than 1.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Cisco Employee

Re: Multicast Problems Between VLANs on 3750

Also since you only have one router, you do not really need to run auto-RP. static RP would be far less complicated.

int lo0

ip pim sparse-mode

interface Vlan3

ip pim sparse-mode

interface Vlan7

ip pim sparse-mode

ip pim rp-address 1.1.1.1

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Community Member

Re: Multicast Problems Between VLANs on 3750

I love coming across a very old post that solves my problem.  This post perfectly described my situation, right down to the hair pulling.  The answer that @Harold Ritter gave also perfectly solved my problem.  The app I was using had TTL set for 1.  Wouldn't have thought to check for that.  

 

FYI, if you want to enable multicast routing across VLANS on a switch, do NOT enable igmp snooping querier.  It won't help and it will be disabled anyways when you enable PIM on the SVI.

Community Member

Re: Multicast Problems Between VLANs on 3750

enable multicast routing and then type following command "Switch2(config)#ip igmp snooping querier".it will send the multicast traffic to intersted receivers only.

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