tap interfaces disabled in linux bridge - Carrier (IFF_RUNNING)

https://serverfault.com/questions/540831/tap-interfaces-always-disabled-in-linux-bridge

tap interfaces always disabled in linux bridge

I have a physical interface eth0, and I want to create two virtual interfaces and bridge them with eth0. For this purpose I do:

#Create the virtual interfaces
tunctl -t tap0
tunctl -t tap1
ifconfig tap0 up
ifconfig tap1 up

#Create the bridge
brctl addbr br0
brctl stp br0 off
brctl addif br0 eth0
brctl addif br0 tap0
brctl addif br0 tap1

#Turning up the bridge
ifconfig br0 up

However my problem if that the tap interfaces always appear disabled in the bridge, and no traffic flows to them.

$brctl show br0
bridge name bridge id       STP enabled interfaces
br0     8000.080027cabeba   no          eth2
                                        tap0
                                        tap1

$brctl showstp br0
br0
 bridge id      8000.080027cabeba
 designated root    8000.080027cabeba
 root port         0            path cost          0
 max age          20.00         bridge max age        20.00
 hello time        2.00         bridge hello time      2.00
 forward delay        15.00         bridge forward delay      15.00
 ageing time         300.01
 hello timer           0.00         tcn timer          0.00
 topology change timer     0.00         gc timer         298.42
 flags          


eth2 (1)
 port id        8001            state            forwarding
 designated root    8000.080027cabeba   path cost          4
 designated bridge  8000.080027cabeba   message age timer      0.00
 designated port    8001            forward delay timer   12.97
 designated cost       0            hold timer         1.24
 flags          

tap0 (2)
 port id        8002            state              disabled
 designated root    8000.080027cabeba   path cost        100
 designated bridge  8000.080027cabeba   message age timer      0.00
 designated port    8002            forward delay timer    0.00
 designated cost       0            hold timer         0.00
 flags          

tap1 (3)
 port id        8003            state              disabled
 designated root    8000.080027cabeba   path cost        100
 designated bridge  8000.080027cabeba   message age timer      0.00
 designated port    8003            forward delay timer    0.00
 designated cost       0            hold timer         0.00
 flags    

Is there any way to set the tap interfaces in forwarding state? I do not understand why they are not because STP is disabled.

Cheers

Daniel

==========================================================================================

Answer

Carrier (IFF_RUNNING) is only set on a tap when a user has the device handle open.

For a persistent tap created with tunctl, you need an application which attaches to the tap, eg:

• http://backreference.org/2010/03/26/tuntap-interface-tutorial/

or

        http://blog.csdn.net/ztguang/article/details/72890346