第1个模块：网络需求-2-Catalyst 6500基本架构 CCNP交换部分中文版 教学课件.pptVIP

* So looking at the switch fabric in a bit more detail. What is a crossbar fabric? Well, it basically provides multiple conflict-free paths between the different modules in the chassis. This compared with the classic bus, which is essentially a shared medium – there is arbitration, and only one device can have access to the bus bandwidth at any given time, and then everyone connected to the bus sees every packet that crosses the bus. Not so with the crossbar fabric – you can have multiple packets traversing the fabric at any given time, so this is not a shared medium, we are providing dedicated bandwidth to and from each slot in the system to every other slot, so you can have multiple parallel conversations. Now in all the chassis but the 13 slot, we send 2 fabric channels to each slot. We have 18 fabric channels, and up to 9 slots, so the math is easy, 18 divided by 9 is 2. Now in the 13 slot chassis, obviously the math doesn’t work out – there are not enough channels to send 2 to every slot, so instead, we send a single fabric channel to slots 1 through 8, and then we send 2 channels to the bottom 5 slots. Now as I mentioned earlier, what this means is that dual-fabric modules – the 6816, the 6748, the 6704 – will not work in the upper slots of the 13 slot chassis. So these slots are getting half of the bandwidth provided to the lower slots. * So let’s look specifically at the SFM and SFM2 –these provide a 256 gigabit per second fabric when used in conjunction with Supervisor 2. To access this bandwidth, you need to use the CEF256 or dCEF256 switching modules. These are basically any module with 65xx in the model number, like 6516 or 6548. And then there is the 6816-GBIC, which is dual-fabric attached – so what does that mean, if it is dual fabric attached? Right, you can’t put that module in the upper 8 slots of the 6513. Now the SFM fabric channels run at 8 Gbps – that’s engineering math, meaning we can send 8 gig into the fabric and take 8 gig out at the same t