[ovs-discuss] VLAN tagged and untagged with VM and real switch

[Qin, Xiaohong]

In the old days, bridge was the gear to connect multiple segments, it has the learning, flooding, and even spanning tree capabilities. But normally you don't use a bridge to configure VLAN, so switch is a superset of bridge that in addition to port address learning, flooding, and spanning tree, it can support VLAN for multiple ports, behind the scene, it introduced the concepts of "cloverleaf intersection", "cut-through switching", "store-and-forward switching", and "fragment-free switch", and CAM, tCAM fast memory access technologies.  The first transparent bridge was developed by DEC and first switch was by Kalpana.

Dennis Qin

-----Original Message-----
From: Brian Candler [mailto:b.candler at pobox.com] 
Sent: Monday, April 21, 2014 10:27 AM
To: Qin, Xiaohong; Alex; discuss openvswitch.org
Subject: Re: [ovs-discuss] VLAN tagged and untagged with VM and real switch

On 21/04/2014 17:52, Qin, Xiaohong wrote:
> I was quickly scanning through this FAQ link,
>
> https://raw.githubusercontent.com/openvswitch/ovs/master/FAQ
>
> found this Q/A paragraph,
>
> Q: I thought Open vSwitch was a virtual Ethernet switch, but the
>     documentation keeps talking about bridges.  What's a bridge?
>
> A: In networking, the terms "bridge" and "switch" are synonyms.  Open
>     vSwitch implements an Ethernet switch, which means that it is also
>     an Ethernet bridge.
>
> In the physical network world, bridge and switch are two different gears, they are not synonyms.
I believe the FAQ is correct - a bridge and a switch are synonyms, in the physical world too.

Sometimes, people talk about a switch with two ports as being a bridge. 
But a two-port bridge is still a switch, and vice versa.

Otherwise, would you care to explain your point with some concrete examples?