multicast across multiple switches

sheldonj22 · ‎03-27-2017

Hopefully someone can help me with this issue. I have 2 servers that are trying to cluster with multicast within the same vlan, i verified with tcpdump they are both sending IGMP / multicast but aren't receiving it. There are 3 switches between them: [server] => [Top of rack switch] => [6509] => [Top of rack switch] => [server] . There are zero configs regarding multicast/IGMP on any of the switches, thus no mrouter port. It seems that the problem is defined here [ http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/68131-cat-multicast-prob.html ]. I was going to statically assign the mrouter port to be the port-channel going to the core switch, but when I lab this out, the two multicast clients are able to communicate which leads me to believe that the mrouter port is not the problem.

Is there something I'm misunderstanding about this scenario or will adding the port-channel as the mrouter port fix my issue and why could it not be needed in my lab environment?

Jon Marshall · ‎03-27-2017

From the topology you posted that certainly seems to be the issue you are facing. I usually recommend enabling the IGMP snooping querier function which was introduced for this type of thing but you can define the mrouter port if you want. They should both fix your issue.

As to why you are not seeing it in the lab all I can say is that from my own experience and time spent on these forums multicast with IGMP snooping can behave differently depending on the switch models you are using.

I am assuming that in your lab IGMP snooping is enabled which it should be by default.

Jon

sheldonj22 · ‎03-27-2017

Thanks for your reply. Would I need to set the mrouters on the core switch as well or will setting them on the two TOR switches work?

My Lab environment, which two linux clients using omping are able to send/recieve multicast from each other, is described below with shortened versions of the configs, if I can figure out why my lab is acting differently itd make me a lot confident that I won't impact our production environment.

[Client] => [Bottom 3560 ] --|port channel |--> [ Top 2960 ] --|port channel |--> [Middle 3550 ] => [Client]

----------

hostname top
!
interface Port-channel1
switchport mode trunk
!
interface Port-channel2
switchport mode trunk
!
interface FastEthernet0/1
switchport mode trunk
channel-group 1 mode active
!
interface FastEthernet0/3
switchport mode trunk
channel-group 1 mode active
!
interface FastEthernet0/22
!
interface FastEthernet0/23
switchport mode trunk
channel-group 2 mode desirable
!
interface FastEthernet0/24
switchport mode trunk
channel-group 2 mode desirable
!
interface GigabitEthernet0/1
!
interface GigabitEthernet0/2
!
interface Vlan1
ip address 10.1.1.101 255.255.255.0
no ip route-cache
!

-----------

hostname middle
!
ip subnet-zero
ip routing
spanning-tree extend system-id
no spanning-tree vlan 1
no spanning-tree vlan 13
!
interface Port-channel1
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
!
interface FastEthernet0/1
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
channel-group 1 mode passive
!
interface FastEthernet0/3
switchport trunk encapsulation dot1q
switchport mode trunk
no ip address
channel-group 1 mode passive
!
interface FastEthernet0/15
switchport mode access
no ip address
!
interface FastEthernet0/16
switchport mode access
no ip address
!
interface FastEthernet0/17
switchport mode access
no ip address
!
interface FastEthernet0/23
switchport mode access
no ip address
!
interface FastEthernet0/24
switchport trunk encapsulation dot1q
switchport mode access
no ip address
!
interface Vlan1
ip address 10.1.1.100 255.255.255.0
ip igmp version 3
!

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

hostname bottom
!
spanning-tree mode pvst
spanning-tree etherchannel guard misconfig
spanning-tree extend system-id
no spanning-tree vlan 1,13
spanning-tree vlan 2 priority 24576
!
vlan internal allocation policy ascending
!
!
!
interface Port-channel1
switchport trunk encapsulation dot1q
switchport mode trunk
!
interface FastEthernet0/1
switchport trunk encapsulation dot1q
switchport mode trunk
channel-group 1 mode auto
!
interface FastEthernet0/2
!
interface FastEthernet0/3
switchport trunk encapsulation dot1q
switchport mode trunk
channel-group 1 mode auto
!
interface FastEthernet0/4
!
interface FastEthernet0/6
!
interface FastEthernet0/7
!
interface FastEthernet0/8
!
interface FastEthernet0/9
!
interface FastEthernet0/24
!
interface GigabitEthernet0/1
!
interface GigabitEthernet0/2
!
interface Vlan1
ip address 10.1.1.102 255.255.255.0
!

Jon Marshall · ‎03-27-2017

I'll have a look at the configs in more detail but as to your first question that is why I would use the IGMP snooping querier function because you would only need to enable it on the 6500 which definitely supports it.

Jon