This document describes how to configure and troubleshoot Layer 2 (L2) multicast for Virtual Machines (VMs) upon setup of the Cisco Unified Computing System (UCS), Cisco Nexus 1000V Series switches (N1kV), and Cisco Nexus 5000 Series switches (N5k).
Cisco recommends that you have knowledge of these topics:
The information in this document is based on these software and hardware versions:
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command or packet capture setup.
Multicast was initially designed to use Layer 3 (L3) functionality, where multiple hosts from a network subscribe to a multicast address. The new trend is to use L2 multicast functionality, where traffic flows between VMs that participate in a multicast application across hosts on the same VLAN. Such multicast traffic stays within the same L2 domain and does not need a router.
When there is no multicast router in the VLAN that originates the queries, you must configure an Internet Group Management Protocol (IGMP) snooping querier in order to send membership queries. IGMP snooping is enabled by default on the UCS, N1kV, and N5k. You can enable IGMP snooping querier on either the UCS or a N5k, dependent upon the scope of the L2 multicast. If there are multicast receivers outside of the UCS, configure the snooping querier on the N5k.
When an IGMP snooping querier is enabled, it sends out periodic IGMP queries that trigger IGMP report messages from hosts that want to receive IP multicast traffic. IGMP snooping listens to these IGMP reports in order to establish appropriate forwarding.
The IGMP snooping software examines IGMP protocol messages within a VLAN in order to discover the interfaces that are connected to hosts or other devices interested in receiving this traffic. With the interface information, IGMP snooping can reduce bandwidth consumption in a multi-access LAN environment in order to avoid a flood of the entire VLAN. The IGMP snooping feature tracks the ports that are attached to multicast-capable routers in order to help manage the forwarding of IGMP membership reports. Also, the IGMP snooping software responds to topology change notifications.
Use this section in order to configure L2 multicast for VMs.
Here are some important notes about the network setup in this example:
There is no need to configure two queriers in the same VLAN (16). If there are multicast receivers outside of the UCS, configure the snooping querier on the N5k. If the multicast traffic is within the UCS domain, then create the snooping querier on the Cisco Unified Computing System Manager (UCSM).
Here is an example configuration of an IGMP querier on a N5k:
vlan 16
ip igmp snooping querier 172.16.16.2
!
int vlan 16
ip address 172.16.16.2/24
no shut
The querier IP address does not need to be for a switched-virtual interface, and it can be a different IP address within the same subnet of VLAN 16.
Complete these steps in order to configure the IGMP querier for UCS:
Use this section in order to verify that your configuration works correctly.
Verify that the multicast receivers TEST VM and AD-1 VM have joined multicast stream 239.14.14.14, from which MCAST VM sources traffic. This image shows that multicast receiver TEST VM receives the stream:
The N1kV snooping output shows the Group Address and the Veths of the multicast receiver, not the Veth of the VM that sources the multicast traffic (as expected):
This N1kV output shows the active ports for multicast and the IGMP querier:
At the host level, you can verify that multicast traffic is received by the VMs that participate. This output shows the VM AD-1, which is on Module 3 of the Virtual Supervisor Module (VSM):
This output shows the VM TEST, which is on Module 4 of the VSM:
This UCS output shows the active ports for multicast and the Group Address:
This UCS snooping output for VLAN 16 verifies that the querier is configured on the UCSM and the N5k, and it shows that only the querier on the N5k is currently active (as expected):
On the N5k, confirm that multicast group address 239.14.14.14 and the active port-channel is connected to the UCS Fabric Interconnects (FIs):
This section provides information that you can use in order to troubleshoot your configuration.
Here is a list of basic caveats about multicast in the L2 domain:
Revision | Publish Date | Comments |
---|---|---|
1.0 |
27-Jan-2014 |
Initial Release |