Re: [fedora-virt] Cannot set MTU on bridge

[Andrew Cathrow]

Did you try setting the mtu on the physical interface?

-------- Original Message --------
 From: Ian Pilcher 
 Sent: Thu, 01/11/2012 06:22 PM
 To: [e-mail]
 CC: 
 Subject: [fedora-virt] Cannot set MTU on bridge

I am trying to create a bridge for use as an iSCSI storage network.  The
iSCSI target will run on the host (Fedora 17) and the initiators will
all run on KVM VMs.  Thus, no physical interface will be added to the
bridge.

For optimum performance, I want to use jumbo frames on the storage
network, so I've created ifcfg-stor0 as follows:

IPADDR=192.168.0.254
    NETMASK=255.255.255.0
    DEVICE=stor0
    ONBOOT=yes
    TYPE=Bridge
    IPV6INIT=no
    DELAY=0
    STP=off
    NM_CONTROLLED=no
    MTU=9000

When starting the interface with ifup, I get "RTNETLINK answers:
Invalid argument", and the MTU is set to 1500.

Trying to set the MTU with ifconfig gives me "SIOCSIFMTU: Invalid
argument".

The workaround I've found so far is to attach a dummy device with the
desired MTU to the bridge:

DEVICE=dummy0
    ONBOOT=yes
    MTU=9000
    IPV6INIT=no
    BRIDGE=stor0
    NM_CONTROLLED=no

This works, and it's even possible to remove the dummy device after the
MTU is set.

The questions is how can I do this without this awful hack?

TIA!

Cannot set MTU on bridge

[Ian Pilcher]

On 11/01/2012 06:03 PM, Andrew Cathrow wrote:
> Did you try setting the mtu on the physical interface?

There is no physical interface.  (See below.)
> -------- Original Message --------
>  From: Ian Pilcher 
>  Sent: Thu, 01/11/2012 06:22 PM
>  To: [e-mail]
>  CC: 
>  Subject: [fedora-virt] Cannot set MTU on bridge
>
> I am trying to create a bridge for use as an iSCSI storage network.  The
> iSCSI target will run on the host (Fedora 17) and the initiators will
> all run on KVM VMs.  Thus, no physical interface will be added to the
> bridge.
>
> For optimum performance, I want to use jumbo frames on the storage
> network, so I've created ifcfg-stor0 as follows:
> IPADDR=192.168.0.254
> NETMASK=255.255.255.0
> DEVICE=stor0
> ONBOOT=yes
> TYPE=Bridge
> IPV6INIT=no
> DELAY=0
> STP=off
> NM_CONTROLLED=no
> MTU=9000
>
> When starting the interface with ifup, I get "RTNETLINK answers:
> Invalid argument", and the MTU is set to 1500.
>
> Trying to set the MTU with ifconfig gives me "SIOCSIFMTU: Invalid
> argument".
>
> The workaround I've found so far is to attach a dummy device with the
> desired MTU to the bridge:
> DEVICE=dummy0
> ONBOOT=yes
> MTU=9000
> IPV6INIT=no
> BRIDGE=stor0
> NM_CONTROLLED=no
>
> This works, and it's even possible to remove the dummy device after the
> MTU is set.
>
> The questions is how can I do this without this awful hack?
>
> TIA!