Linux Ethernet Bridging - Apr 2007 - [Bridge] Cannot ping to the board when changing loop configuration

Hi all,

I am running a bridge with STP 'on' on an arm-linux
board. I have two ethernet ports on the bridge both
connected to a single switch thus creating a loop.
Using brctl on the board, I can see one of the port
being blocked and the other forwarding. I can ping the
board from a remote PC connected to the same switch.

    _______ 1       _______       ____
   |       |-------|       |_____|    |
   | Board |xxx----|Switch |     | PC |
   |_______|2      |_______|     |____|


When I disconnect the cable from the forwarding port
(port 1), I can see both the ports going into the
forwarding state. However, when I try to ping the
board again from the remote PC, I am not able to reach
the board anymore. Sniffing the packets show that the
board can receive arp requests on the port 2 but the
arp response is not generated. Sniffing packets on the
bridge interface show arp queries being sent to PC
instead.

Please help.


--Prashant


		
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Prashant Agrawal wrote:
| Hi all,
|
| I am running a bridge with STP 'on' on an arm-linux
| board. I have two ethernet ports on the bridge both
| connected to a single switch thus creating a loop.
| Using brctl on the board, I can see one of the port
| being blocked and the other forwarding. I can ping the
| board from a remote PC connected to the same switch.
|
|     _______ 1       _______       ____
|    |       |-------|       |_____|    |
|    | Board |xxx----|Switch |     | PC |
|    |_______|2      |_______|     |____|
|
|
| When I disconnect the cable from the forwarding port
| (port 1), I can see both the ports going into the
| forwarding state. However, when I try to ping the
| board again from the remote PC, I am not able to reach
| the board anymore. Sniffing the packets show that the
| board can receive arp requests on the port 2 but the
| arp response is not generated. Sniffing packets on the
| bridge interface show arp queries being sent to PC
| instead.
|
| Please help.
|
|
| --Prashant
|
It's possible I'm making this up, but could it perhaps be that the STP
code is
detecting the loop and changing things to "fix" it? Does it work with
STP turned
off?

- - Patrick Bogen
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I did tried disabling STP, but it seems to create a
loop and the board keeps recieving looped packets. 

I now have a packet sniffer on the board. When I ping
to the board, I saw ARP request packets being sent to
the forwarding port and being handed over to br0. br0
does generate ARP response but it never reaches the
destination nor is it visible on the port at which the
ARP request were received. 

The strange thing is that after a wait of about 20
minutes, I am able to start pinging the board
again!!!!!
Any clues?????


		
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