A >And that's exactly what would happen if you did the inter-VLAN routing on a >router too, using subinterfaces for each VLAN/ IP subnet. :-) > >And, if it were a high-end router, it could do this at wire speed and would >have a RIB and FIB, just like someone else described for the 6500. The 7500 >router has had that sort of architecture for years, if I'm not mistaken. >Howard has given us lots of examples of other high-end routers that have >this sort of architecture. Of course, these high-end routers are probably >way more expensive than the so-called L3 switch and probably have all sorts >of features that you might not need in a campus network.
Last I check, extreme make some pretty cheap bridges with integrated routing :) Naturally, to get a bunch of packet processing without mortgaging forwarding capacity, you'll end up spending more bucks. Howard's point about the relevance of wire speed routing in the enterprise is dead on though - most folks don't need it and wouldn't make use of it even if they had it. >So, we're back to the first answer. The difference between a router and a L3 >switch is marketing. Also economics. > >Sorry, I just had to play devil's advocate. What a shame that Cisco has >mangled this so much in their intro training materials. > >Priscilla > > > ... > > > > Does that help? > > > > Oh - and I think you meant to say "layer 3 switching" is a > > marketing term, > > not scientific or engineering in nature. ... you said "layer 3 > > routing" ... > > Thanks! > > TJ > > [EMAIL PROTECTED] > > > > > > -----Original Message----- > > From: DeVoe, Charles (PKI) [mailto:[EMAIL PROTECTED] > > Sent: Wednesday, February 26, 2003 7:45 AM > > To: [EMAIL PROTECTED] > > Subject: RE: L3 Switching Huh???? [7:63728] > > > > 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. > > > > 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? > > 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. > > Switching is based on MAC address. > > Routing is based on IP address. > > > > I believe the term "layer 3 routing" is a marketing term, not > > scientific or > > engineering in nature. > > >****************************************************************************** > > The information in this email is confidential and may be > > legally > > privileged. Access to this email by anyone other than the > > intended addressee is unauthorized. If you are not the > > intended > > recipient of this message, any review, disclosure, copying, > > distribution, retention, or any action taken or omitted to be > > taken > > in reliance on it is prohibited and may be unlawful. If you > > are not > > the intended recipient, please reply to or forward a copy of > > this > > message to the sender and delete the message, any attachments, > > and any copies thereof from your system. > > >****************************************************************************** Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=63928&t=63728 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
