Date: Wed, 16 Feb 2000 07:16:25 -0700 From: "Duke Normandin" <01031149@3web.net> To: <cjclark@home.com> Cc: <freebsd-questions@FreeBSD.org> Subject: Re: Routed and public IPs Message-ID: <004201bf7889$5fd042c0$2f9fc5d1@webserver>
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On Tuesday, February 15, 2000 7:54 PM Crist J. Clark wrote: >On Tue, Feb 15, 2000 at 06:18:10AM -0700, Duke Normandin wrote: >> On Monday, February 14, 2000 11:45 AM Crist J. Clark wrote: >> >> >On Mon, Feb 14, 2000 at 10:35:19AM -0700, Duke Normandin wrote: >> >> Although I'm not involved in this thread, directly or indirectly, >> >> I want to thank you for such a great reply. I can't believe you >> >> and Ruslan et al -- I'm green with envy. I've saved this thread >> >> for future reference, however would you mind defining for me (in >> >> laymen's terms) the concept of bridge(4)ing? Something like: >> >> "bridging is using a box to bridge a gap between (public & private >> >> IPs??) or ?? ". I don't want your info to go to waste on this >> >> newbie, so I thought I'd ask. Tia... >> > >> >A bridge is a network device that operates at layer two of the IP >> >stack, the link layer. Hubs and switches are the other most common >> >devices that work at layer two. A bridge does not know anything about >> >IP addresses, and most often, it simply forwards _all_ packets it >> >receives on one interface to the other. However, it is possible to run >> >a filter on the bridge, as was the whole point of the thread you are >> >following. >> > >> >I personally have only used a simple bridge that passes all >> >packets. Some users want two computers (running different OSes) in >> >their offices. There is only one RJ-45 connection coming into the >> >room. Rather than give them each a hub, one computer gets an extra NIC >> >and bridges for the other. As far as the second computer is concerned, >> >its on the same LAN. >> >> >> Thanks....to your reply and a tutorial I found on the net, I now >> understand that a bridge is an external, physical device. Quoting >> this tutorial: >> >> "In contrast to hubs, which are physical-level devices, bridges >> operate on Ethernet frames and thus are layer-2 devices. In fact, >> bridges are full-fledged packet switches that forward and filter >> frames using the LAN destination addresses. When a frame comes into >> a bridge interface, the bridge does not just copy the frame onto all >> of the other interfaces. Instead, the bridge examines the destination >> address of the frame and attempts to forward the frame on the >> interface that leads to the destination." >> >> However, I'm confused with your term "physical-level device" as >> opposed to "link-level (layer-2) devices. Are not both physical >> devices? Do not both operate on Ethernet frames? I now understand >> that a bridge will "examine" an Ethernet frame, as opposed to a hub, >> i.e., "in-one-ear, out-the-other" ;^). Thanks for your time. > >_My_ term "physical-level?" The physical layer is the bottom layer of >the IP stack. The layer where they push electrons around and all of >that fun RF stuff. As someone brought up in the thread, the quote >above refers to a "hub" as a physical-layer device. That is a device >that simply gets some electronic signal in and then sends the same >signal out. > >Unfortunately, the terminology is not that clean. For example, the >description of a bridge above seems a lot more like the description of >a switch. And if a hub is a layer one and switch layer two, what the >heck is the very common item called a "switched hub?" > >But getting back to the original theme, when we talk about bridging in >FreeBSD networking, what it boils down to is passing packets bewteen >interfaces on a host without altering the packets' hardware addresses. Thanks! I see that "semantics" is an ever-ending issue, no matter what the topic. I've attached a graphic from the U. of Edinburgh which I believe speaks to this thread quite lucidly. You and Lowell spurred me to "find the 'mother' of all networking tutorials OR die" and I did at http://www.erg.abdn.ac.uk/users/gorry/eg3561/road-map.gif http://www.erg.abdn.ac.uk/users/gorry/eg3561/syllabus.html Hopefully, other interested newbies on this list will use the above links (as I now will). Thanks! -duke To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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