Re: [Linux-ATM-General] br2684 : sent packets truncated in VC routed mode

[Eric K. (contractor) <ek...@cm...>]

On Wed Jul 27 16:43:33 +0200 2011, Pascal Hambourg wrote:
> [Sorry for the previous message with an empty subject]
> 
> Hello,
> 
> I tried to setup an IPoA over ADSL connection in VC routed mode with
> br2684ctl at a friend's house :
> 
> # br2684ctl -c 0 -e 1 -p 0 -a 8.36
> 
> and configured the nas0 interface with ifconfig. No error message, but no
> replies to sent packets were received. Then I setup a CLIP interface with
> atmarp in VC mode instead :
> 
> # atmarp -c 0
> # ifconfig atm0 <address> netmask <netmask> up mtu 1500
> # atmarp -s <gateway> 8.36 null
> 
> and the connection worked well.
> 
> Back home, I investigated using atmtcp to print sent PDUs, and found out
> that in PDUs generated by br2684 the 14 first bytes were missing, while
> they were present when generated by atmarp.
> 
> Looking at net/atm/br2684.c in the kernel source, in function
> br2684_xmit_vcc() I found :
> 
> 	} else { /* e_vc */
> 		if (brdev->payload == p_bridged) {
> 			skb_push(skb, 2);
> 			memset(skb->data, 0, 2);
> 		} else { /* p_routed */
> 			skb_pull(skb, ETH_HLEN);
> 
> Hmm, indeed 14 bytes is just the size of an ethernet header, but it makes
> no sense on a point-to-point interface. I commented out the last line and
> rebuilt the br2684 module, and now sent PDUs look complete. However I have
> not been able to test for real yet as I don't have an IPoA connection.
> 
> My kernel version is 2.6.32.x but this part has not changed in newer
> versions.
> 
> The line was added by commit 7e903c2ae36efb526eacab3b25d00e90424bd8a8 atm:
> [br2864] fix routed vcmux support
> 
> Any comments ? Maybe I missed something, I can hardly believe
> such an issue could have remained unnoticed for such a long time.

Changing the -p option to "1" will put an ethernet header in each pdu.
See rfc 1483 section 4.1 for a description of the "routed" configuration
(-p 0).

# br2684ctl -c 0 -e 0 -p 1 -a 8.36