DeVoe, Charles (PKI) wrote: > > OK, let me try this again. I am trying to figure out the > difference between > conventional layer 3 routing and layer 3 switching. A little > background. I > am currently working towards my CCNA (have been for about 3 > years). At any > rate, everything I read and look at says that > switching/bridging is a layer > 2 function, routing is a layer 3 function. > > Either I don't have a good grasp of the OSI model, switching, > routing, VLANs > or all of the above.
It sounds like you got it. Don't worry about the terminology so much. You got the concepts and that's what's important. See a few more comments below. > > The network: > > Host A 10.1.1.2 MAC 00.AA > Host B > 10.1.2.2 MAC 00.BB > | 10.1.1.1 MAC 01.AA 10.1.2.1 MAC > 02.BB | > switch > A-----------------------Router-------------------------switch B > 10.1.1.0/24 10.1.2.0/24 > > This is an ethernet network. Both segments are connected by a > traditional > router say a 2500. > In this instance the router interfaces are subnet A 10.1.1.1, > and subnet B > 10.1.2.1 > > For simplicity, assume ARP cache is empty. > Host A wishes to ping Host B > End user on Host A enters - ping 10.1.2.2 > The IP packet places the source address 10.1.1.2 and the > destination address > 10.1.2.2 into the packet. > The IP protocol examines the IP address and based on the IP > address > determines this is in another subnet. > An ARP request goes out for 10.1.1.1 (default gateway) and the > MAC address > is found. > The DLL then places the source MAC address 00.AA and the > destination MAC > 01.AA into the frame. > The frame then goes out the wire to the destination MAC. > The router interface sees this frame as destined for itself. It > de-encapsulates the frame removing the MAC addresses. The > router then > examines the IP address, based on the routing table it knows > the destination > port. > The router leaves the same IP source (10.1.1.2) and destination > (10.1.2.2) > in the packet. > The frame is rebuilt with the new MAC address of source 02.BB > and > destination 00.BB > Host B grabs this packet and does it's thing. > > Now, if I replace the router with a 6509 switch, with routing, > how does the > process change? The process is logically the same. I'm not familiar enough with the architecture of the 6509 switch to provide the details, but it looks like others have, so that's good. The important thing is that you understand the traffic flow and what goes in the address fields in the packets. That's great. There are senior network admins that don't get that. Seriously. The CCIE written tests this sort of thing and every so often we get clueless questions about it from people who think they are going to jump right into CCIE as long as we force-feed them the fundamentals. You are doing the right thing by getting down the fundamentals while still studying for CCNA. > Said 6509 would be equipped with a 10/100 card so that the > hosts are now > directly connected. The router interface is now a virtual > interface, there > is no physical interface. Which is another question. How does > the 6509 > determine this virtual address? > > Am I correct? > Inter VLAN communication cannot occur without a router. Yes. > Switching is based on MAC address. > Routing is based on IP address. The word switching is used in a more generic way too and has been for hundreds of years. Switching means forwarding, relaying, routing. Please do not insist that it only happens at L2, despite what the stupid books say. As I have already said, it's not true that it's just a marketing term. It is a good engineering term that the marketing people stole. Train tracks have equipment that switches trains. Telephone equipment switches voice conversations. Electrical devices switch current. An internetworking device switches digital data. For years, Cisco tried to get people to see the same thing that Howard is still trying to get people to see, which is that there are two sets of tasks: one related to learning paths to destinations and one related to forwarding data. For years Cisco called this second path switching. I say this just in the hopes that you will see that even Cisco has used the term switching to mean forwarding, long before L2 switches existed or before marketing people made up the L3 switch term. Priscilla > > I believe the term "layer 3 routing" is a marketing term, not > scientific or > engineering in nature. > > Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63915&t=63728 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
