xwen01
1 Copper

port mirroring and multicast

Hi,

I am trying to do some test of multicast in local network. The scenario I am trying to test is as follows:

1. Server 1 is the source of multicast traffic and it sends multicast to group 239.1.1.1. Server 2 is on the same VLAN and is able to receive multicast from group 239.1.1.1. Both Server 1 and Server 2 use iperf for the test. 

2. Then I configured port mirroring on powerconnect 6248 switch. The source port is configured as the port Server 2 is connected, and destination port (which is on another VLAN) is the port another server (Server  3) is connected. 

3. I am expecting to receive the same multicast on Server 3. However, I cannot receive any multicast either using iperf or tcpdump.

No multicast routing protocol configured. No igmp snooping enabled. 

Any help is appreciated.

Calvin

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11 Replies

Re: port mirroring and multicast

It is possible the multicast packets are timing out. It looks like you would apply this to the VLAN interface where the multicast is entering the switch.  ie .. the VLAN that Server 1 is on.  

ip multicast ttl-threshold

Use the ip multicast ttl-threshold command in Interface Configuration mode to apply a ttlvalue to a routing interface. ttlvalue is the TTL threshold which is applied to the multicast Data packets forwarded through the interface.

The following example applies a ttlvalue of 5 to the VLAN 15 routing interface.

console(config)#interface vlan 15

console(config-if-vlan15)#ip multicast ttl-threshold 5

Do you still have configuration for a VLAN on the destination mirror port?  

Can you provide the output of this command for the destination mirror port that is connected to Server 3?

console#show interfaces detail ethernet x/x

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xwen01
1 Copper

Re: port mirroring and multicast

Thanks for the reply. 

I tried the multicast ttl-threshold - set to 5, however, it didn't help. I still got no multicast on the mirror destination. Here is the output: 

console#show interfaces detail ethernet 1/g36

Port Type Duplex Speed Neg Admin Link
State State
----- ------------------------------ ------ ------- ---- ----- -----
1/g36 Gigabit - Level Full 1000 Auto Up Up


Port Description
---- --------------------------------------------------------------------------
1/g36

Flow Control:Enabled

Thanks again for your help. 
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xwen01
1 Copper

Re: port mirroring and multicast

Some update:

I am able to see the icmp traffic on the mirror destination. But still no multicast traffic.

Thanks for any help.

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vt1012
3 Argentium

Re: port mirroring and multicast

Hello!

Somtimes there is another TTL/hop count in the application itself.  When routing between vlans I had to increase this for it to work on another VLAN.  I used a rather larger number like 16 and it worked.  Don't know if your app has this setting, but I did see one when I setup VLC media player.     

Another thing you should probably look at is using diffserv to do this. 

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xwen01
1 Copper

Re: port mirroring and multicast

Barrett, thanks for the reply. It should not be TTL in the application, since I can receive multicast on the mirror source interface. The problem is even I see multicast on the mirror source, I don't see it on mirror destination.

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Highlighted

Re: port mirroring and multicast

Barrett may have a pretty good point.  If it gets to the source port then not to the destination.  Something is not keeping it alive, blocking or incorrect configuration.

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xwen01
1 Copper

Re: port mirroring and multicast

Thanks. However, I did set application TTL to 16, and still cannot make it work. I am using iperf for the test. The command for the multicast source:

iperf -c 239.1.1.1 -u -T 16 -t 100 -i 1

where -T 16 should set the TTL to 16. And I even cannot see any udp traffic been mirrored to the mirror destination, by using "tcpdump udp -i ethx". (ethx is the interface connects to the mirror destination interface)

Any other possible problems? Thanks.

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vt1012
3 Argentium

Re: port mirroring and multicast

hmmm.  I am not too familiar with iperf, but from what I've read it seems the source (server) has the -s switch whereas the client has the -c switch.  I also read that the source must bind the multicast address using the -B switch.  So here is one example:

Source:  iperf -s -u -B 239.1.1.1  (and of cource the TTL would go here)

Client:    iperf -c -239.1.1.1 -u  

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xwen01
1 Copper

Re: port mirroring and multicast

Actually, it is the other way around. The client is the one sends out the multicast packets and sets the TTL, where the server just listens to the multicast group (binding to the multicast group address).

Can you suggest other tool for testing? I can give it a try. Thanks for your help.  

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