Como posso ativar quadros jumbo em uma interface ponte Xen unida?

Question

Eu tenho um servidor Debian Jessie 8.2 servindo como um host Xen VM. O servidor possui duas interfaces de rede físicas que são ligadas entre si usando o LACP. Há também uma interface xenbr0 . Eu gostaria de habilitar quadros jumbo, no entanto eu sou incapaz de. Aqui está a configuração da rede:

auto eth0
iface eth0 inet manual
   bondmaster bond0
   mtu 9000

auto eth1
iface eth1 inet manual
   bondmaster bond0
   mtu 9000

auto bond0
iface bond0 inet manual
   bond-mode 4
   bond-miimon 100
   bond-lacp-rate 1
   bond-slaves eth0 eth1
   mtu 9000

auto xenbr0
iface xenbr0 inet static
   bridge_ports bond0
   address 10.0.0.12
   gateway 10.0.0.1
   netmask 255.255.255.0
   mtu 9000

Depois de adicionar o MTU a cada interface, executei sudo ifdown bond0 && sudo ifup bond0 . O MTU ainda é relatado como 1.500. Eu tentei o mesmo com a interface xenbr0 , no entanto, recebo a seguinte saída:

user@host:~$ sudo ifdown xenbr0 && sudo ifup xenbr0
ifdown: interface xenbr0 not configured

Waiting for xenbr0 to get ready (MAXWAIT is 32 seconds).
RTNETLINK answers: File exists
Failed to bring up xenbr0.

Aqui está a saída de ip a , sem interfaces virtuais para convidados da VM:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP group default qlen 1000
    link/ether e8:94:f6:08:aa:30 brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP group default qlen 1000
    link/ether e8:94:f6:08:aa:30 brd ff:ff:ff:ff:ff:ff
4: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue master xenbr0 state UP group default 
    link/ether e8:94:f6:08:aa:30 brd ff:ff:ff:ff:ff:ff
17: xenbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default 
    link/ether e8:94:f6:08:aa:30 brd ff:ff:ff:ff:ff:ff
    inet 10.0.0.12/24 brd 10.0.0.255 scope global xenbr0
       valid_lft forever preferred_lft forever
    inet6 2001:****:****:****:****:****:****:****/64 scope global mngtmpaddr dynamic 
       valid_lft 2591736sec preferred_lft 604536sec
    inet6 fe80::ea94:f6ff:fe08:aa30/64 scope link 
       valid_lft forever preferred_lft forever

O que eu fiz de errado?