Subject: Re: [PATCH] bonding: correct the MAC address for "follow" fail_over_mac policy

From: Nikolay Aleksandrov <[email-masked]>
Date: Thu, 16 Jul 2015 11:24:16 +0200

On 07/16/2015 10:30 AM, Ding Tianhong wrote:
> The "follow" fail_over_mac policy is useful for multiport devices that
> either become confused or incur a performance penalty when multiple
> ports are programmed with the same MAC address, but the same MAC
> address still may happened by this steps for this policy:
> 
> 1) echo +eth0 > /sys/class/net/bond0/bonding/slaves
>    bond0 has the same mac address with eth0, it is MAC1.
> 
> 2) echo +eth1 > /sys/class/net/bond0/bonding/slaves
>    eth1 is backup, eth1 has MAC2.
> 
> 3) ifconfig eth0 down
>    eth1 became active slave, bond will swap MAC for eth0 and eth1,
>    so eth1 has MAC1, and eth0 has MAC2.
> 
> 4) ifconfig eth1 down
>    there is no active slave, and eth1 still has MAC1, eth2 has MAC2.
> 
> 5) ifconfig eth0 up
>    the eth0 became active slave again, the bond set eth0 to MAC1.
> 
> Something wrong here, then if you set eth1 up, the eth0 and eth1 will have the same
> MAC address, it will break this policy for ACTIVE_BACKUP mode.
> 
> This patch will fix this problem by finding the old active slave and
> swap them MAC address before change active slave.
> 
> Signed-off-by: Ding Tianhong <[email-masked]>
> ---
>  drivers/net/bonding/bond_main.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 

This doesn't seem to be true:
~# cat /sys/class/net/bond0/bonding/fail_over_mac 
follow 2
root@debian:~# ip l sh eth1
3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
root@debian:~# ip l sh eth2
4: eth2: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
root@debian:~# ip l sh bond0
26: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default 
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff

*eth1 is the first and active slave and bond0 has taken its mac.
Now trying your steps:
Step 3) (bringing down the active eth1)
root@debian:~# ip l set eth1 down
root@debian:~# ip l sh bond0
26: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default 
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
root@debian:~# ip l sh eth1
3: eth1: <BROADCAST,MULTICAST,SLAVE> mtu 1500 qdisc pfifo_fast master bond0 state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
root@debian:~# ip l sh eth2
4: eth2: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff

*The mac addresses of eth1 and eth2 are correctly swapped, so far so good.

Step 4) (bringing down the active eth2)
root@debian:~# ip l set eth2 down
3: eth1: <BROADCAST,MULTICAST,SLAVE> mtu 1500 qdisc pfifo_fast master bond0 state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST,SLAVE> mtu 1500 qdisc pfifo_fast master bond0 state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
26: bond0: <NO-CARRIER,BROADCAST,MULTICAST,MASTER,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default 
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff

*eth2 has kept the mac address of the bond and they're both down now

Step 5) (bring eth1 up again and observe the macs)
~# ip l set eth1 up
3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST,SLAVE> mtu 1500 qdisc pfifo_fast master bond0 state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
26: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default 
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff

*The macs are correctly swapped and there's no such bug. 

Step 6(?) bring eth2 up
~# ip l set eth2 up
3: eth1: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST,SLAVE,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master bond0 state UP mode DEFAULT group default qlen 1000
    link/ether 52:54:00:4f:a5:99 brd ff:ff:ff:ff:ff:ff
26: bond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default 
    link/ether 52:54:00:3f:47:69 brd ff:ff:ff:ff:ff:ff

*Still correct.

Also the mac address that gets set is dev_addr which is changed when
the swapping is done, if you'd like to get the original mac address
you should be using slave->perm_hwaddr.

Cheers,
 Nik