[Bridge] Small packets

Leigh Sharpe lsharpe at pacificwireless.com.au
Sun Oct 28 22:40:42 PDT 2007


-----Original Message-----
From: Stephen Hemminger [mailto:shemminger at linux-foundation.org] 
Sent: Monday, 29 October 2007 4:12 PM
To: Leigh Sharpe
Cc: bridge at lists.linux-foundation.org
Subject: Re: [Bridge] Small packets

On Mon, 29 Oct 2007 15:37:52 +1100
"Leigh Sharpe" <lsharpe at pacificwireless.com.au> wrote:

>> Which seems to bridge OK. However, I have noticed that the bridge
>> appears to be truncating some packets. In particular, I am worried
>> about packets such as IP ACK's, which are entering the bridge as
>> 64-byte packets, but coming out the other side as 60-byte packets.
>> As I recall, the smallest valid ehternet packet is 64 bytes. The
>> bridge seems to be removing any padding in the packet and sending it
>> on it's way as a packet smaller than the minimum ethernet packet
>> size. Looking at the packet distribution on other devices connected
>> to the bridge, it seems to be doing the same to lots of other
> packets, too. Anybody got any idea why the bridge might be truncating
> packets? Any idea why it's sending 60-byte packets, when the minimu
> should be 64? Or where to tell it to pad all packets out to 64 bytes?
> Leigh.

>What hardware? It could be a driver bug.
>Also if you use VLAN's then the driver may send 60 byte packet (because
>of the 4 byte VLAN tag).

Standard e1000 hardware.
The packets being bridged contain a VLAN tag, which is included in the
60 bytes.

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