OVS – Remove Interface from Bond

I needed to temporary ‘steal’ an interface from a server for other purposes. The problem is the interface was one of two interfaces used in an Open vSwitch bond.

I found a couple of ways to remove it, but my goal was to do it with either no service interruption or as little interruption as possible. One of the recommendations I found online was to delete the bond interface and recreate it but due to inexperience with OVS I didn’t want to risk this.

The method I selected was to make database commands to remove the interface instead; I found this post on the OVS discussion mailing list which was very helpful.

Interface Removal

My goal was to remove port eth5 from bond0:

root@server:~# ovs-vsctl show
0d4a7b35-119c-4e18-88c1-dc474bd8f458
    Bridge "vmbr0"
        Port "tap122i0"
            tag: 60
            Interface "tap122i0"
...
        Port "bond0"
            Interface "eth5"
            Interface "eth9"

This was done in a single command:

ovs-vsctl --id=@eth5 get Interface eth5 -- remove Port bond0 interfaces @eth5

There was a very short interruption of traffic (2-3 seconds) after which everything continued to worked fine. If I am feeling a bit more brave one day I would do some more testing; I suspect the interruption could have been avoided completely by downing the port on the switch side first

Adding/Replacing Interface

To add either the same or a different interface back into the bond a single command can be used:

ovs-vsctl --id=@eth5 create Interface name=eth5 -- add Port bond0 interfaces @eth5

Verification

For those not familiar with checking the status of the bond interface:

root@server:~# ovs-appctl bond/show bond0
---- bond0 ----
bond_mode: balance-tcp
bond may use recirculation: yes, Recirc-ID : 1
bond-hash-basis: 0
updelay: 0 ms
downdelay: 0 ms
next rebalance: 7296 ms
lacp_status: negotiated
active slave mac: 3c:fd:fe:0b:6f:42(eth9)

slave eth5: enabled
        may_enable: true
...

slave eth9: enabled
        active slave
        may_enable: true

As the bond interface is using LACP:

root@server:~# ovs-appctl lacp/show bond0
---- bond0 ----
        status: active negotiated
        sys_id: 3c:fd:fe:0b:6f:40
        sys_priority: 65534
        aggregation key: 1
        lacp_time: fast

slave: eth5: current attached
        port_id: 1
        port_priority: 65535
        may_enable: true

        actor sys_id: 3c:fd:fe:0b:6f:40
        actor sys_priority: 65534
        actor port_id: 1
        actor port_priority: 65535
        actor key: 1
        actor state: activity timeout aggregation synchronized collecting distributing

        partner sys_id: d4:04:ff:fc:64:80
        partner sys_priority: 127
        partner port_id: 55
        partner port_priority: 127
        partner key: 5
        partner state: activity timeout aggregation synchronized collecting distributing

slave: eth9: current attached
        port_id: 2
        port_priority: 65535
        may_enable: true

        actor sys_id: 3c:fd:fe:0b:6f:40
        actor sys_priority: 65534
        actor port_id: 2
        actor port_priority: 65535
        actor key: 1
        actor state: activity timeout aggregation synchronized collecting distributing

        partner sys_id: d4:04:ff:fc:64:80
        partner sys_priority: 127
        partner port_id: 54
        partner port_priority: 127
        partner key: 5
        partner state: activity timeout aggregation synchronized collecting distributing

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