Hi all,

I want to use brctl to setup a software bridge in my computer. I want to know the overhead caused by distributing layer 2 frames.

Does any one have that experience, e.g., cpu cycles to packets ratio??

Thanks in advance.

Shawn

You mean "Physical Layer"?

If yes, depends what you are going to use.

I think bridge is located at the osi-2 layer, not physical layer.
I mean the overhead caused by software bridge, say, forwarding one frame costs how many cpu cycles?

Thanks,
Shawn

According to this, software bridge should be in third or even may be in forth layer.

Transport
(Layer 4) This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

Network
(Layer 3) This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.

Data Link
(Layer 2) At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

Physical
(Layer 1) This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

May be that helps you: http://www.usenix.org/events/usenix0...tml/index.html

Thanks. But the xen paper only investigates the optimizations on the receive path. It primarily reduces copying overhead and scheduling overhead.
The virtual bridging overhead seems not a culprit of the virtual network inefficiency. Do you think so?

Am I getting it wrong on bridging???
Please reference:
http://en.wikipedia.org/wiki/Network_bridge
http://www.faqs.org/docs/Linux-HOWTO...STP-HOWTO.html

In fact, I have very much interest in virtualization (xen).

Shawn

I thought that soft bridge should be at layer 3, but never mind.

You know, it is very easy to check, there is utility "powertop", it can show CPU interrupts. So if you make bridge, for example between 10BaseT and 100BaseT, you can check processor load. Or just look to /proc/interrupts