MTU change

[brucexx]

I need to adjust MTU on an interface, not Proxmox interface but the interface facing ceph to make it more efficient over 10Gbps network.

It is a bonded interface let's say bond0, bonding eth2 and 3 added to vmbr1 interface.

I was planning to just do this after hours by issuing ifconfig bond0 mtu <size>. The node is in production but again I will be doing it after hours so minimal load.

Any comments, advise , anything can go wrong ?

 

[brucexx]

Just realized that this will only change the mtu temporarily. So what about changing it via /etc/network/interfaces adding the mtu size on bond0 and issuing ifdown bond0 && ifup bond0 would that do the job or I need to reboot ?

Thx

 

[udo]

Just realized that this will only change the mtu temporarily. So what about changing it via /etc/network/interfaces adding the mtu size on bond0 and issuing ifdown bond0 && ifup bond0 would that do the job or I need to reboot ?

Thx

Hi,
look here - 8972 bacause vlan-tagging - without 9000 also:

auto bond2
iface bond2 inet static
  bond-downdelay 200
  bond-updelay 200
  bond-miimon 100
  bond-mode active-backup
  bond-slaves eth2.3 eth3.3
  bond-primary eth2.3
  pre-up ( ifconfig eth2 mtu 9000 && ifconfig eth3 mtu 9000 )
  mtu 8972

Udo

 

[robhost]

You can simply use: ip link set dev eth0 mtu 9000 i.e.

The change in /etc/network/interfaces should also be made for persistence.

 

[brucexx]

Thank you,

Udo - what about the pre-up command, is it necessary to first set the mtu on the physical interface ethX, and then on bondX ? ..or you need it because you use the logical interfaces/subinterfaces eth2.3, eth3.3 to start with ?

I have dedicated only and was wondering if I need that setting or the mtu 9000 would suffice.

Thank you again.

 

[udo]

Thank you,

Udo - what about the pre-up command, is it necessary to first set the mtu on the physical interface ethX, and then on bondX ? ..or you need it because you use the logical interfaces/subinterfaces eth2.3, eth3.3 to start with ?

I have dedicated only and was wondering if I need that setting or the mtu 9000 would suffice.

Thank you again.

Hi,
it's not enough to set the mtu of an bridge to 9000 if the connected devices stay with an mtu of 1500.
The pre-up command set the right mtu to the bonded devices.

Udo

 

[RobFantini]

Udo - something has changed in network code since you wrote your advise.

I tried this:

       pre-up ( ifconfig eth2 mtu 9000 && ifconfig eth3 mtu 9000 )
       mtu 8972

and eth* ended at mtu 8972 ..

so i tried post-up instead of pre-up , same result.

after deleting the pre-up line, using just 'mtu 9000 ' the bond and eth* all came up at 9000

I rebooted for changes to take effect.

Question - you mentioned to reserve some mtu units for vlan . I wonder if that is now an issue?