From mboxrd@z Thu Jan 1 00:00:00 1970 From: Grant Taylor Subject: Re: Bridges Date: Thu, 19 Aug 2010 10:49:05 -0500 Message-ID: <4C6D5271.901@riverviewtech.net> References: <4C6B10CA.4090604@abpni.co.uk> <4C6C55C8.5000905@riverviewtech.net> <4C6C65CD.6090707@plouf.fr.eu.org> <4C6CAA60.60808@riverviewtech.net> <4C6CDE4E.7000609@plouf.fr.eu.org> <4C6D44E3.7050608@riverviewtech.net> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: netfilter-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Mail List - Netfilter On 08/19/10 09:56, Jan Engelhardt wrote: > "Layer 3 switching" is usually a bullshit bingo word for routing. *chuckle* I like how you flop your opinion on the table Jan'. :-) I'm actually having a discussion about routing vs l3 switching with a friend and colleague, prompted by this thread. It is my belief (and my colleague / friend can't say that I'm wrong) that both routing and layer 3 switching will take an ethernet frame that is coming in one interface with one set of source / dest MAC addresses and forward it out another interface with a different set of source / dest MAC addresses in the process of forwarding the IP packet on to its ultimate destination. (They both will also do some other things like validating checksum, decrement the TTL, etc.) IMHO the real (and only) difference (as I (mis)understand it) between routing and layer 3 switching is /how/ each accomplishes its task. Routing is traditionally a software in CPU operation where as layer 3 switching is hardware ASICs. Software in CPU is quit a bit slower than optimized hardware ASICs. Thus l3 switches can usually much more closely approach wire speed than routers can. Skim the following article on Cisco's web site. Link - Layer 2 and Layer 3 Switch Evolution - The Internet Protocol Journal - Volume 1, No. 2 - Cisco Systems - http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_1-2/switch_evolution.html As the article points out, layer 3 switching is done for the simple routing tasks. Any time there is complexity involved, the packets are passed up to the CPU / software to be routed traditionally. Along the same lines, it is my belief that (currently) layer 3 switches can't switch between desperate network technologies. I.e. Ethernet / FDDI or Ethernet / Token Ring or Ethernet / ATM can not be layer 3 switches, they require traditional routing because of the differences in the physical topologies. Grant. . . .