[Bridge] brctl problem: broadcast doesn't get through

[Bridge] brctl problem: broadcast doesn't get through

[Ireneusz Szcześniak]

Hi,

I'm creating a bridge, and then add to it two tap interfaces. No 
physical interface is added to the bridge. These are the commands:

brctl addbr test
ip tuntap add mode tap tap0
ip tuntap add mode tap tap1
ifconfig test up
ifconfig tap0 up
ifconfig tap1 up
brctl addif test tap0
brctl addif test tap1

The problem is that the bridge doesn't seem to work correctly. I sent 
through tap0 some broadcast frames (WOL frames), and they didn't reach 
tap1. I was sending packets with:

etherwake -b -i tap0 00:00:00:00:00:00

The tshark command for tap0 showed the frames being sent with tap0, 
but another tshark for tap1 didn't show them.

Then I added to tap0 the IP address 192.168.10.1/24, and did:

arping 192.168.1.2

I saw ARP request broadcast frames on tap0, but they didn't reach tap1.

This is the output of ifconfig for test, tap0, and tap1 interfaces:

root@computer:~# ifconfig test
test Link encap:Ethernet HWaddr 02:07:b1:eb:2c:2a
inet6 addr: fe80::944b:d9ff:fe10:b240/64 Scope:Link
UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:19 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:3377 (3.2 KiB)

root@computer:~# ifconfig tap0
tap0 Link encap:Ethernet HWaddr 02:07:b1:eb:2c:2a
inet addr:192.168.10.0 Bcast:192.168.10.255 Mask:255.255.255.0
inet6 addr: fe80::7:b1ff:feeb:2c2a/64 Scope:Link
UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:278 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)

root@computer:~# ifconfig tap1
tap1 Link encap:Ethernet HWaddr b2:ee:2c:f9:d5:0d
inet6 addr: fe80::b0ee:2cff:fef9:d50d/64 Scope:Link
UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:19 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)

The output of the brctl:

root@computer:~# brctl show
bridge name bridge id STP enabled interfaces
pan0 8000.000000000000 no
test 8000.0207b1eb2c2a no tap0
tap1
root@computer:~# brctl showmacs test
port no mac addr is local? ageing timer
1 02:07:b1:eb:2c:2a yes 0.00
2 b2:ee:2c:f9:d5:0d yes 0.00

The output of route:

root@computer:/home/iszczesniak# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.2.0 0.0.0.0 255.255.255.0 U 2 0 0 eth1
192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 tap0
169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 eth1
0.0.0.0 192.168.2.1 0.0.0.0 UG 0 0 0 eth1

What am I doing wrong?


Thanks,
Irek

-- 
Ireneusz (Irek) Szczesniak
http://www.irkos.org

Re: [Bridge] brctl problem: broadcast doesn't get through

[Stephen Hemminger]

On Sun, 24 Apr 2011 17:04:47 +0200
Ireneusz Szcześniak <irek.szczesniak@gmail.com> wrote:

> Hi,
> 
> I'm creating a bridge, and then add to it two tap interfaces. No 
> physical interface is added to the bridge. These are the commands:
> 
> brctl addbr test
> ip tuntap add mode tap tap0
> ip tuntap add mode tap tap1
> ifconfig test up
> ifconfig tap0 up
> ifconfig tap1 up
> brctl addif test tap0
> brctl addif test tap1
> 
> The problem is that the bridge doesn't seem to work correctly. I sent 
> through tap0 some broadcast frames (WOL frames), and they didn't reach 
> tap1. I was sending packets with:
> 
> etherwake -b -i tap0 00:00:00:00:00:00
> 
> The tshark command for tap0 showed the frames being sent with tap0, 
> but another tshark for tap1 didn't show them.
> 
> Then I added to tap0 the IP address 192.168.10.1/24, and did:
> 
> arping 192.168.1.2
> 
> I saw ARP request broadcast frames on tap0, but they didn't reach tap1.
> 
> This is the output of ifconfig for test, tap0, and tap1 interfaces:
> 
> root@computer:~# ifconfig test
> test Link encap:Ethernet HWaddr 02:07:b1:eb:2c:2a
> inet6 addr: fe80::944b:d9ff:fe10:b240/64 Scope:Link
> UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:19 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:0
> RX bytes:0 (0.0 B) TX bytes:3377 (3.2 KiB)
> 
> root@computer:~# ifconfig tap0
> tap0 Link encap:Ethernet HWaddr 02:07:b1:eb:2c:2a
> inet addr:192.168.10.0 Bcast:192.168.10.255 Mask:255.255.255.0
> inet6 addr: fe80::7:b1ff:feeb:2c2a/64 Scope:Link
> UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:0 errors:0 dropped:278 overruns:0 carrier:0
> collisions:0 txqueuelen:500
> RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
> 
> root@computer:~# ifconfig tap1
> tap1 Link encap:Ethernet HWaddr b2:ee:2c:f9:d5:0d
> inet6 addr: fe80::b0ee:2cff:fef9:d50d/64 Scope:Link
> UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:0 errors:0 dropped:19 overruns:0 carrier:0
> collisions:0 txqueuelen:500
> RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
> 
> The output of the brctl:
> 
> root@computer:~# brctl show
> bridge name bridge id STP enabled interfaces
> pan0 8000.000000000000 no
> test 8000.0207b1eb2c2a no tap0
> tap1
> root@computer:~# brctl showmacs test
> port no mac addr is local? ageing timer
> 1 02:07:b1:eb:2c:2a yes 0.00
> 2 b2:ee:2c:f9:d5:0d yes 0.00
> 
> The output of route:
> 
> root@computer:/home/iszczesniak# route -n
> Kernel IP routing table
> Destination Gateway Genmask Flags Metric Ref Use Iface
> 192.168.2.0 0.0.0.0 255.255.255.0 U 2 0 0 eth1
> 192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 tap0
> 169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 eth1
> 0.0.0.0 192.168.2.1 0.0.0.0 UG 0 0 0 eth1
> 
> What am I doing wrong?
> 
> 
> Thanks,
> Irek
> 

00:00:00:00:00:00 is an invalid ethernet address and is always dropped
by bridge to be in compliance with standards.  Use a real ethernet address,
for kernel devices there is a convenience routine to generate a random ethernet
address.

-- 

Re: [Bridge] brctl problem: broadcast doesn't get through

[Ireneusz Szcześniak]

On 24.04.2011 18:40, Stephen Hemminger wrote:

> 00:00:00:00:00:00 is an invalid ethernet address and is always dropped
> by bridge to be in compliance with standards.  Use a real ethernet address,
> for kernel devices there is a convenience routine to generate a random ethernet
> address.

Thanks for your input.  The 00:00:00:00:00:00 address is not used as 
the destination address of the frame, because I passed the -b option 
of the etherwake tool, and so the broadcast address was used.  Also, 
the frames generated by arping are broadcasted, and they don't reach tap1.

In my tests tap0 and tap1 are not used by any program that connects to 
them; the tap0 and tap1 interfaces have been added and are reported by 
ifconfig.  However, if I instruct qemu to use tap0, and then in the 
virutal machine I make the very same tests, I can see broadcast frames 
on tap1.

-- 
Ireneusz (Irek) Szczesniak
http://www.irkos.org

Re: [Bridge] brctl problem: broadcast doesn't get through

[Ireneusz Szcześniak]

Now I think I understand better what is happening in my case.  I guess 
that my configuration can be depicted as follows:

application
that connects
to tap1
  |   ^
  |   |
  | tap1
  | intf
  |   |
  v   |
bridge "test"
  |   ^
  v   |
tap0 |
intf |
  |   |
  v   |
application
that connects
to tap0

The reasoning for the arrows above is as follows:

1. When I send a broadcast frame to tap0 with "etherwake -b -i tap0 
00:00:00:00:00:00", this frame doesn't reach the bridge, but it 
reaches the application connected to the tap0 interface.

2. It seems that the tap0 interface is transparent, i.e. the messages 
that originate at the bridge and that should be sent to the 
application that connects to tap0 are not consumed by the tap0 
interface.  Listening with tcpdump or tshark on tap0 shows these messages.

3. When I send in the application connected to tap0 a frame with the 
destination address of the tap0 interface, this frame is seen at the 
bridge.

If my reasoning is wrong, please let me know.


Thanks.
Irek

On 24.04.2011 17:04, Ireneusz Szcześniak wrote:
> Hi,
>
> I'm creating a bridge, and then add to it two tap interfaces. No
> physical interface is added to the bridge. These are the commands:
>
> brctl addbr test
> ip tuntap add mode tap tap0
> ip tuntap add mode tap tap1
> ifconfig test up
> ifconfig tap0 up
> ifconfig tap1 up
> brctl addif test tap0
> brctl addif test tap1
>
> The problem is that the bridge doesn't seem to work correctly. I sent
> through tap0 some broadcast frames (WOL frames), and they didn't reach
> tap1. I was sending packets with:
>
> etherwake -b -i tap0 00:00:00:00:00:00
>
> The tshark command for tap0 showed the frames being sent with tap0, but
> another tshark for tap1 didn't show them.
>
> Then I added to tap0 the IP address 192.168.10.1/24, and did:
>
> arping 192.168.1.2
>
> I saw ARP request broadcast frames on tap0, but they didn't reach tap1.
>
> This is the output of ifconfig for test, tap0, and tap1 interfaces:
>
> root@computer:~# ifconfig test
> test Link encap:Ethernet HWaddr 02:07:b1:eb:2c:2a
> inet6 addr: fe80::944b:d9ff:fe10:b240/64 Scope:Link
> UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:19 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:0
> RX bytes:0 (0.0 B) TX bytes:3377 (3.2 KiB)
>
> root@computer:~# ifconfig tap0
> tap0 Link encap:Ethernet HWaddr 02:07:b1:eb:2c:2a
> inet addr:192.168.10.0 Bcast:192.168.10.255 Mask:255.255.255.0
> inet6 addr: fe80::7:b1ff:feeb:2c2a/64 Scope:Link
> UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:0 errors:0 dropped:278 overruns:0 carrier:0
> collisions:0 txqueuelen:500
> RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
>
> root@computer:~# ifconfig tap1
> tap1 Link encap:Ethernet HWaddr b2:ee:2c:f9:d5:0d
> inet6 addr: fe80::b0ee:2cff:fef9:d50d/64 Scope:Link
> UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:0 errors:0 dropped:19 overruns:0 carrier:0
> collisions:0 txqueuelen:500
> RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
>
> The output of the brctl:
>
> root@computer:~# brctl show
> bridge name bridge id STP enabled interfaces
> pan0 8000.000000000000 no
> test 8000.0207b1eb2c2a no tap0
> tap1
> root@computer:~# brctl showmacs test
> port no mac addr is local? ageing timer
> 1 02:07:b1:eb:2c:2a yes 0.00
> 2 b2:ee:2c:f9:d5:0d yes 0.00
>
> The output of route:
>
> root@computer:/home/iszczesniak# route -n
> Kernel IP routing table
> Destination Gateway Genmask Flags Metric Ref Use Iface
> 192.168.2.0 0.0.0.0 255.255.255.0 U 2 0 0 eth1
> 192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 tap0
> 169.254.0.0 0.0.0.0 255.255.0.0 U 1000 0 0 eth1
> 0.0.0.0 192.168.2.1 0.0.0.0 UG 0 0 0 eth1
>
> What am I doing wrong?
>
>
> Thanks,
> Irek
>


-- 
Ireneusz (Irek) Szczesniak
http://www.irkos.org