[Bridge] bridge is not forwarding the packet

rahul bhardwaj rahul_bhardwaj36in at yahoo.co.in
Mon Sep 29 00:06:55 PDT 2008

Hi Leigh,

Thanks a lot for your reply,

Leigh, your suggestion solves the current problem. But it might not 
be exactly we what we want.I just want know like, is it possible to get the same behavior when 
eth0 and eth0.15 are on different bridges?
 With Regards 

Rahul Bhardwaj 


--- On Wed, 24/9/08, Leigh Sharpe <lsharpe at pacificwireless.com.au> wrote:
From: Leigh Sharpe <lsharpe at pacificwireless.com.au>
Subject: RE: [Bridge] bridge is not forwarding the packet
To: "rahul bhardwaj" <rahul_bhardwaj36in at yahoo.co.in>, bridge at lists.linux-foundation.org
Cc: "Stephen Hemminger" <shemminger at vyatta.com>
Date: Wednesday, 24 September, 2008, 4:23 PM

Hi Rahul,
 If you're certain that your problem isn't as Stephen suggested, you 
might want to have a look at this:

(From http://ebtables.sourceforge.net/brnf-faq.html )
How do I let vlan-tagged traffic go through a vlan 
bridge port and the other traffic through 
a non-vlan bridge port? 
Suppose eth0 and eth0.15 are ports of br0. Without 
countermeasures all traffic, including 
traffic vlan-tagged with tag 15, entering the
physical device eth0 will go through the bridge port 
eth0. To make the 15-tagged traffic go 
through the eth0.15 bridge port, use the following
ebtables rule: 
ebtables -t broute -A BROUTING -i eth0 --vlan-id 15 
With the above rule, 15-tagged traffic will enter the 
bridge on the physical device eth0, will 
then be brouted and enter the bridge port 
eth0.15, the vlan header will be stripped, after which the packet is bridged. The packet thus enters the BROUTING 
chain twice, the first time with input 
device eth0 and the second time with input device eth0.15.
The other chains are only traversed once. All other 
traffic will be bridged with input device 
This describes how to make sure your VLAN tagged traffic ends up on the bridge you want.


From: bridge-bounces at lists.linux-foundation.org 
[mailto:bridge-bounces at lists.linux-foundation.org] On Behalf Of rahul 
Sent: Tuesday, 23 September 2008 11:32 PM
bridge at lists.linux-foundation.org
Cc: Stephen 
Subject: Re: [Bridge] bridge is not forwarding the 

    Hi Stephen,

Thanks for your very prompt 


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      Actually my problem is not 
      related to MAC address restrictions from wireless interface/driver. The 
      problem lies mainly in multiple bridges for different vlans. Since 
      bridging happens first, the packet ends up on wrong bridge and gets 
      discarded form that bridge.  If Vlan handling is 
      done prior to bridge handling, my setup will work fine.  
      is also another thing which I did not understand. When we add an interface 
      to vlan, the newly created interface’s hard_header is set to 
      vlan_dev_hard_header function. This vlan_dev_hard_header adds the vlan tag 
      for outing packet. 
      Interestingly this happens 
      after bridging code hand over the packet to interface. Conversely when the 
      packet is received, interface should remove the vlan tag and hand over the 
      packet to bridge. But we are seeing that bridge code is executing prior to 
      vlan handling. 

--- On Mon, 22/9/08, Stephen 
      Hemminger <shemminger at vyatta.com> wrote:

        Stephen Hemminger <shemminger at vyatta.com>
Subject: Re: [Bridge] 
        bridge is not forwarding the packet <Urgent, Please reply 
To: "rahul bhardwaj" 
        <rahul_bhardwaj36in at yahoo.co.in>
        bridge at lists.linux-foundation.org
Date: Monday, 22 September, 2008, 
        8:33 AM

On Mon, 22 Sep 2008 16:24:00 +0530 (IST)
rahul bhardwaj <rahul_bhardwaj36in at yahoo.co.in> wrote:

> Hello to all,
> I am stating my problem below in detail so that you all can understand it
> I am having setup of Linux box. In that box I am having one Ethernet
interface eth0 and one wireless interface ath0. I have also configured one vlan
port as eth0.100 with the
 help of vconfig (vconfig add eth 100).  Now I have
created two bridges br1 and br100. I have added eth0 into br1 so br1 is having
only one interface. I have added ath0 and eth0.100 into br100. Physically eth0
is connected to a switch which is configured to handle vlan 100. DHCP server is
also running into that switch to provide IP address to wireless stations. This
is all about my setup.
> After this I am associating one wireless station with the ath0. After
successful association station issues a dhclient to get ip address, which
reaches to ath0 interface of my Linux box. ath0 bridges that request to
eth0.100. Now eth0.100 adds it's vlan tags and forward that request to the
switch. Because switch is configured to support vlan 100, so it process the dhcp
request and send back the dhcp response with vlan tag 100. 
> Now I don't know but this response is not reaching to ath0. I
putted wireshark and figured out that those dhcp responses are reaching on eth0
and as eth0 is part of br1 so this packet is reaching to br1 which is just
discarding them all. So the wireless station is not getting the ip address.
According to me eth0 should give these packets to eth0.100 port instead of br1.
Or what I mean to say first vlan handling should be done priror then  bridge
handling. Do I need to change something into Linux kernel for that or there is
some other problem with my setup?
> Can anybody help me in this? If anybody want more detail I will provide. I
am using Linux 2.6.15 kernel. Any kind of help will be much appreciated. 
> With Regards 
> Rahul Bhardwaj 

Full bridging to wireless requires WDS which Linux wireless does not

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