[Bridge] Small packets

Leigh Sharpe lsharpe at pacificwireless.com.au
Sun Oct 28 21:37:52 PDT 2007

Hi All,
 I have a bridge set up thusly:
brctl addbr br0                                 # Create the bridge.

brctl addif br0 eth2                            # Add eth2
brctl addif br0 eth3                            # And eth3

brctl setfd br0 0                               # Forward immediately.

brctl stp br0 off                               # Turn off Spanning

ifconfig eth2 up                                # bring up eth2
ifconfig eth3 up                                # Bring up eth3
ifconfig br0 up                                 # Bring up the bridge.

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 Sharpe
Network Systems Engineer
Pacific Wireless
Ph +61 3 9584 8966
Mob 0408 009 502
Helpdesk 1300 300 616
email lsharpe at pacificwireless.com.au
<blocked::mailto:lsharpe at pacificwireless.com.au> 
web www.pacificwireless.com.au
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