Even the STP is enabled through brctl stp switch on on a looped network, the packets cannot be forwarded successfully. Please note that if there is no loop in the network, then everything is ok.
The problem is described as followed.
I have three Linux boards (i.e., SW1, SW2, SW3) with the ring topology as shown:
SW1
/ \
SW2 ———— SW3
The IP configurations are:
SW1:192.168.20.2
SW2:192.168.20.3
SW3:192.168.20.4
Each Linux board has 4 physical ports, and the connections are:
SW1.swp2 <---> SW2.swp2
SW1.swp0 <---> SW3.swp1
SW2.swp3 <---> SW3.swp3
The bridge configuration of SW1 is as shown below, the others are as same as this one except for the IP address of "switch".
ifconfig switch 192.168.20.2 # the "192.168.20.2" is the IP of SW1,
ip link set switch up
ip link set swp0 master switch && ip link set swp0 up
ip link set swp1 master switch && ip link set swp1 up
ip link set swp2 master switch && ip link set swp2 up
ip link set swp3 master switch && ip link set swp3 up
route add default gw 192.168.20.1
brctl stp switch on
ip link set up dev switch
The STP is enabled successfully:
brctl show switch
bridge name bridge id STP enabled interfaces
switch 8000.06f5bc4466d2 yes swp0
swp1
swp2
swp3
The STP status for SW1:
brctl showstp switch
switch
bridge id 8000.06f5bc4466d2
designated root 8000.067b22fa77a2
root port 1 path cost 4
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 300.00
hello timer 0.00 tcn timer 0.00
topology change timer 0.00 gc timer 239.55
flags
swp0 (1)
port id 8001 state forwarding
designated root 8000.067b22fa77a2 path cost 4
designated bridge 8000.067b22fa77a2 message age timer 19.82
designated port 8002 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
swp1 (2)
port id 8002 state disabled
designated root 8000.06f5bc4466d2 path cost 100
designated bridge 8000.06f5bc4466d2 message age timer 0.00
designated port 8002 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
swp2 (3)
port id 8003 state forwarding
designated root 8000.067b22fa77a2 path cost 4
designated bridge 8000.06f5bc4466d2 message age timer 0.00
designated port 8003 forward delay timer 0.00
designated cost 4 hold timer 1.41
flags
swp3 (4)
port id 8004 state disabled
designated root 8000.06f5bc4466d2 path cost 100
designated bridge 8000.06f5bc4466d2 message age timer 0.00
designated port 8004 forward delay timer 0.00
designated cost 0 hold timer 0.00
The STP status for SW2:
brctl showstp switch
switch
bridge id 8000.9a32d1ec24fe
designated root 8000.067b22fa77a2
root port 4 path cost 4
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 300.00
hello timer 0.00 tcn timer 0.00
topology change timer 0.00 gc timer 58.07
flags
swp0 (1)
port id 8001 state disabled
designated root 8000.9a32d1ec24fe path cost 100
designated bridge 8000.9a32d1ec24fe message age timer 0.00
designated port 8001 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
swp1 (2)
port id 8002 state disabled
designated root 8000.9a32d1ec24fe path cost 100
designated bridge 8000.9a32d1ec24fe message age timer 0.00
designated port 8002 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
swp2 (3)
port id 8003 state blocking
designated root 8000.067b22fa77a2 path cost 4
designated bridge 8000.06f5bc4466d2 message age timer 19.43
designated port 8003 forward delay timer 0.00
designated cost 4 hold timer 0.00
flags
swp3 (4)
port id 8004 state forwarding
designated root 8000.067b22fa77a2 path cost 4
designated bridge 8000.067b22fa77a2 message age timer 19.43
designated port 8004 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
The STP status for SW3:
brctl showstp switch
switch
bridge id 8000.067b22fa77a2
designated root 8000.067b22fa77a2
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 300.00
hello timer 0.62 tcn timer 0.00
topology change timer 0.00 gc timer 98.80
flags
swp0 (1)
port id 8001 state forwarding
designated root 8000.067b22fa77a2 path cost 4
designated bridge 8000.067b22fa77a2 message age timer 0.00
designated port 8001 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
swp1 (2)
port id 8002 state forwarding
designated root 8000.067b22fa77a2 path cost 4
designated bridge 8000.067b22fa77a2 message age timer 0.00
designated port 8002 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
swp2 (3)
port id 8003 state forwarding
designated root 8000.067b22fa77a2 path cost 19
designated bridge 8000.067b22fa77a2 message age timer 0.00
designated port 8003 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
swp3 (4)
port id 8004 state forwarding
designated root 8000.067b22fa77a2 path cost 4
designated bridge 8000.067b22fa77a2 message age timer 0.00
designated port 8004 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
In SW1, I ping SW2:
ping 192.168.20.3
PING 192.168.20.3 (192.168.20.3): 56 data bytes
64 bytes from 192.168.20.3: seq=9 ttl=64 time=0.330 ms
64 bytes from 192.168.20.3: seq=37 ttl=64 time=0.291 ms
64 bytes from 192.168.20.3: seq=63 ttl=64 time=0.289 ms
64 bytes from 192.168.20.3: seq=90 ttl=64 time=0.310 ms
64 bytes from 192.168.20.3: seq=117 ttl=64 time=0.305 ms
64 bytes from 192.168.20.3: seq=145 ttl=64 time=0.286 ms
64 bytes from 192.168.20.3: seq=172 ttl=64 time=0.311 ms
As we can see, the ping packets can not be transmitted continually.
Is there any good idea? Again, when I disconnected the loop, the ping is ok.
