Bridges With Single Uplink

  • 30 October 2020
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Nutanix AHV uses Open vSwitch(OVS) to connect to the CVM, the hypervisor and the user VMs to each other and to the physical network on each node. The CVM manages the OVS inside the AHV host. Since the OVS is an open source software switch that behaves like a layer-2 learning switch, it maintains a MAC address table. Each AHV server maintains an OVS instance, managed as a single logical switch through Prism. 

Bonds:

When multiple uplinks are used they are added to a bond acting as a single logical interface, to which the bridge is connected. Open vSwitch (OVS) does not support bonds with single uplink and as workaround we directly connect bridge to single uplink.

WARNING:

Avoid the use of a single uplink configuration and do not attempt to modify a single uplink configuration using manage_ovs if the version of AOS is 5.10.x prior to 5.10.4. 

Warning:

Updating uplinks can cause short network disconnect. It is strongly recommended performing network changes on a single node at the time after making sure that the cluster can tolerate node failure.

Caution:

  • Configuration changes using 'manage_ovs' to an OVS virtual switch bridge configured with a single uplink could result in a network loop.

  • Adding a Physical NIC directly to the bridge can cause an STP storm and broadcast storm if proper precautions are not taken. 

 

Let's configure bridges with single uplink

 

To connect bridge br1 to a single uplink using eth0, run the following command on the CVM:

 

nutanix@cvm:~$ manage_ovs --bridge_name br1 --interfaces eth0 update_uplinks

Attempting to update br1 to use eth1 instead of eth0(if the idea is to swap ports) will create a loop. Be careful !!!

Output:(truncated for clarity)

nutanix@cvm:~$ manage_ovs show_uplinks
Bridge: br1
Bond: eth0
bond_mode: active-backup
interfaces: eth0
lacp: off
lacp-fallback: false
lacp_speed: slow

From host:

[root@ahv ~]ovs-vsctl show
...
Bridge "br1"
...
Port "eth0"
Interface "eth0"

To remove all uplink from bridge:

[root@ahv ~]ovs-vsctl del-port <bridge> <bond>

 

Reference:

AHV | Bridges with single uplink


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