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
Tree.
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.
Regards,
Leigh
Leigh Sharpe
Network Systems Engineer
Pacific Wireless
Ph +61 3 9584 8966
Mob 0408 009 502
Helpdesk 1300 300 616
email lsharpe@pacificwireless.com.au
<blocked::mailto:lsharpe@pacificwireless.com.au>
web www.pacificwireless.com.au
<blocked::http://www.pacificwireless.com.au/>
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On Mon, 29 Oct 2007 15:37:52 +1100 "Leigh Sharpe" <lsharpe@pacificwireless.com.au> wrote:> 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 > Tree. > > 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. > > > > > Regards, > Leigh > > Leigh Sharpe > Network Systems Engineer > Pacific Wireless > Ph +61 3 9584 8966 > Mob 0408 009 502 > Helpdesk 1300 300 616 > email lsharpe@pacificwireless.com.au > <blocked::mailto:lsharpe@pacificwireless.com.au> > web www.pacificwireless.com.au > <blocked::http://www.pacificwireless.com.au/> >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).
-----Original Message----- From: Stephen Hemminger [mailto:shemminger@linux-foundation.org] Sent: Monday, 29 October 2007 4:12 PM To: Leigh Sharpe Cc: bridge@lists.linux-foundation.org Subject: Re: [Bridge] Small packets On Mon, 29 Oct 2007 15:37:52 +1100 "Leigh Sharpe" <lsharpe@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.