[ovs-discuss] OVC port MTU 1500 dhcp-options mtu 9000

Numan Siddique numans at ovn.org
Thu Nov 19 11:40:52 UTC 2020


On Thu, Nov 19, 2020 at 4:48 PM Brendan Doyle <brendan.doyle at oracle.com> wrote:
>
> So It works if I manually configure the br-int MTUs:
>
> #ovs-vsctl set interface vnet1 mtu_request=8900
> #ovs-vsctl set interface vnet1 mtu=8900
> #ovs-vsctl set interface vnet2 mtu_request=8900
> #ovs-vsctl set interface vnet2 mtu=8900#ovs-vsctl get interface vnet2 mtu
> 8900
> # ovs-vsctl get interface vnet1 mtu
> 8900
>
>
> But I'm thinking that I should be able to modify the VM  KVM XLM, to specify an MTU for the openvswitch interface, something like:
>
>   <interface type='bridge'>
>       <mac address='00:13:97:b6:0f:3c'/>
>       <source bridge='br-int'/>
>       <virtualport type='openvswitch'>
>         <parameters interfaceid='e2ce9e04-25f3-11eb-9180-0010e0c3df92'/>
>       </virtualport>
>       <model type='virtio'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
>        <mtu size='8900'/>
>     </interface>
>
>
> Then hopefully the libvert plugin will configure the OVS bridge MTUs to 8900

I think that's what Openstack Nova or any other compute service
would/should do when it  boots a VM.

Numan

>
> Brendan
>
> On 19/11/2020 10:53, Brendan Doyle wrote:
>
> Folks,
>
> I'm trying to get OVN working in a 9000 MTU config so :
>
>  ovn-nbctl list dhcp-option
> _uuid               : 00f684c8-42bb-4fad-a248-f5697926778d
> cidr                : "10.225.1.0/24"
> external_ids        : {}
> options             : {lease_time="3600", mtu="9000", router="10.225.1.1", server_id="10.225.1.1", server_mac="00:13:97:60:de:6a"}
>
> The hypervisor phys interface MTU is 9000, so I know the above should specify MTU of 8950 to account
> for the geneve header, in any case I manually lower the MTU on the VM node but things still don't work.
> And I think the reason is that when I looked at the OVS br-int, I see the OVN port MTU is 1500. How
> do I get OVN to create the br-int port with a 9000/8950 MTU?
>
> Is this something we have to manually configure on the OVS bridge?
>
> ovs-vsctl list interface vnet1
> _uuid               : 49637687-3870-4eea-911a-e22c6c2ef19a
> admin_state         : up
> bfd                 : {}
> bfd_status          : {}
> cfm_fault           : []
> cfm_fault_status    : []
> cfm_flap_count      : []
> cfm_health          : []
> cfm_mpid            : []
> cfm_remote_mpids    : []
> cfm_remote_opstate  : []
> duplex              : full
> error               : []
> external_ids        : {attached-mac="00:13:97:32:18:d6", iface-id="dc5bca80-2948-11eb-96a2-0010e0c3df92", iface-status=active, vm-id="11b14a04-59ed-45e9-9445-665b8847fba7"}
> ifindex             : 26
> ingress_policing_burst: 0
> ingress_policing_rate: 0
> lacp_current        : []
> link_resets         : 1
> link_speed          : 10000000
> link_state          : up
> lldp                : {}
> mac                 : []
> mac_in_use          : "fe:13:97:32:18:d6"
> mtu                 : 1500
> mtu_request         : []
> name                : "vnet1"
> ofport              : 13
> ofport_request      : []
> options             : {}
> other_config        : {}
> statistics          : {collisions=0, rx_bytes=88983, rx_crc_err=0, rx_dropped=0, rx_errors=0, rx_frame_err=0, rx_over_err=0, rx_packets=470, tx_bytes=33425, tx_dropped=0, tx_errors=0, tx_packets=279}
> status              : {driver_name=tun, driver_version="1.6", firmware_version=""}
> type                : ""
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