1 00:00:00,240 --> 00:00:06,160 Note that each stacking module has two ports with which it's used to connect it to another switch 2 00:00:06,160 --> 00:00:07,010 stacking module. 3 00:00:07,440 --> 00:00:13,590 So as an example, if you've got four switches, each switch has a stacking module and four cables are 4 00:00:13,590 --> 00:00:16,350 used to connect the four switches together. 5 00:00:17,010 --> 00:00:22,320 The way to think of this is the switches are a stack of switches in the same rack. 6 00:00:22,890 --> 00:00:26,880 One of the reasons for doing that is that the stacking cables are very short in length. 7 00:00:27,270 --> 00:00:33,600 So it's expected that the switches are physically positioned next to each other or on top of each other. 8 00:00:34,090 --> 00:00:40,110 As an example, some of the Cisco stacking cables are only half a meter in length or one meter in 9 00:00:40,410 --> 00:00:41,910 or three meters in length. 10 00:00:42,630 --> 00:00:47,790 Again, you need to think of a switch stack as a logical single switch. 11 00:00:48,360 --> 00:00:53,430 You may have four physical switches, but logically they're acting as one switch. 12 00:00:54,090 --> 00:01:00,600 One of the switches in the stack becomes the stack master and it's used to control the rest of the switches 13 00:01:00,600 --> 00:01:01,230 in the stack. 14 00:01:01,980 --> 00:01:07,980 The physical stacking cables connect the physical switches to each other and allow for communication 15 00:01:07,980 --> 00:01:09,660 between the switches in the stack. 16 00:01:10,200 --> 00:01:13,980 But the master switch is in control of the stack. 17 00:01:14,490 --> 00:01:21,060 If, as an example, you have four switches in a stack and a frame arrives on switch 4 and needs to 18 00:01:21,060 --> 00:01:22,770 exit out of switch 3 19 00:01:23,400 --> 00:01:30,770 but switch 1 is the master switch switches 1, 3 and 4 only to communicate over the stack 20 00:01:30,810 --> 00:01:37,980 links to forward the frame. Switches 1, 3, and 4 would need to communicate with each other over 21 00:01:37,980 --> 00:01:39,900 the stack links to forward the frame. 22 00:01:40,710 --> 00:01:48,240 Switch 1 being the master switch would match the Ethernet frame to the Mac address table and would 23 00:01:48,240 --> 00:01:51,230 then decide out of which port to forward the frame. 24 00:01:52,110 --> 00:01:55,260 Think of the master switch as the brain of the stack. 25 00:01:56,580 --> 00:02:03,810 Logically, in a topology like this, we have two physical switches, but logically they are a single 26 00:02:03,810 --> 00:02:07,650 switch and the same would be true if we had four switches. 27 00:02:09,080 --> 00:02:15,500 In a policy like this, we may have full access, which is connected via stacking cables, so physically 28 00:02:15,500 --> 00:02:17,000 it would look like this. 29 00:02:23,970 --> 00:02:31,860 But logically, it looks like this the switches appear to be a single switch to the rest of the network, 30 00:02:32,070 --> 00:02:35,440 and you configure them as if they are a single switch. 31 00:02:36,120 --> 00:02:40,100 We now have four uplinks to each distribution switch. 32 00:02:40,680 --> 00:02:46,800 So physically they connected as follows with each axis switch having one connection to each distribution 33 00:02:46,800 --> 00:02:47,330 switch 34 00:02:47,670 --> 00:02:54,540 but logically, we have four physical cables to each distribution switch, which then allows us to use 35 00:02:54,540 --> 00:02:57,230 ether channel to the distribution switch. 36 00:02:57,960 --> 00:03:03,690 So rather than using spanning tree across these uplinks, where one of the ports is forwarding and one 37 00:03:03,690 --> 00:03:05,030 of the ports is blocking. 38 00:03:05,640 --> 00:03:10,310 We've now created an Ether channel to each distribution switch. 39 00:03:10,710 --> 00:03:16,730 This kind of setup simplifies the configuration and management of the network, from a spanning tree 40 00:03:16,740 --> 00:03:17,310 point of view 41 00:03:17,310 --> 00:03:24,240 rather than having six switches involved in the spanning tree, we now only have three switches involved 42 00:03:24,240 --> 00:03:25,080 in the spanning tree. 43 00:03:25,470 --> 00:03:32,070 So it's much easier to configure, much easier to understand, as well as to predict what happens when 44 00:03:32,070 --> 00:03:33,930 there's a failure in the network. 45 00:03:34,590 --> 00:03:41,700 Uploading across an Ether channel is also more efficient than using spanning tree to block one port and 46 00:03:41,700 --> 00:03:43,020 forward on another port.