RE: If bridge have no sub-interfaces, it's status may be still with 'RUNNING'

Hi Stephen,
  When we up a bridge without sub-interfaces,  it has "RUNNING" flag as below. Is it correct or not?

1. brctl addbr br0
2. ifconfig br0 up
3. ifconfig br0 
br0 Link encap:Ethernet HWaddr e6:6c:84:a6:fc:64 
          inet6 addr: fe80::e46c:84ff:fea6:fc64/64 Scope:Link 
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0 
          TX packets:2 errors:0 dropped:0 overruns:0 carrier:0 
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 B) TX bytes:168 (168.0 B)

Best Regards
Kuaikuai Wu

-----Original Message-----
From: Stephen Hemminger [mailto:stephen@networkplumber.org] 
Sent: Saturday, February 14, 2015 2:31 AM
To: Zhu, Yanjun
Cc: netdev; Wu, Kuaikuai; Tao, Yue
Subject: Re: If bridge have no sub-interfaces, it's status may be still with 'RUNNING'

On Fri, 13 Feb 2015 17:57:45 +0800
yzhu1 [off-list ref] wrote:

Hi, all

I made this test on ubuntu 14.04 with kernel 3,19-rc7:

1. brctl addbr br0

2. ifconfig br0 up

3. ifconfig br0 (br0's status is with 'RUNNING')

4. brctl addif br0 eth0

5. brctl delif br0 eth0

6. ifconfig br0 (br0's status is without 'RUNNING')

When there is no sub-interface, the flag "RUNNING" is missing after 
the last sub-interface is removed.

As such, should we keep "RUNNING" flag after the last sub-interface is 
removed?

This is intentional. If there are no active ports in bridge, then we want to tell applications that packets will go nowhere.