1 1 00:00:00,280 --> 00:00:02,020 Coverage and interference. 2 2 00:00:02,020 --> 00:00:03,650 In this lesson, we're going to discuss 3 3 00:00:03,650 --> 00:00:06,230 coverage and interference in wireless networks. 4 4 00:00:06,230 --> 00:00:07,770 These are two of the most common issues 5 5 00:00:07,770 --> 00:00:09,760 we're going to come across when we start troubleshooting 6 6 00:00:09,760 --> 00:00:11,980 our wireless network connections in the field. 7 7 00:00:11,980 --> 00:00:14,310 First, let's talk about coverage. 8 8 00:00:14,310 --> 00:00:16,420 Coverage is a measure of how large of an area 9 9 00:00:16,420 --> 00:00:18,010 around a wireless transmitter 10 10 00:00:18,010 --> 00:00:19,560 there is sufficient signal strength 11 11 00:00:19,560 --> 00:00:21,610 for a wireless device to utilize. 12 12 00:00:21,610 --> 00:00:24,070 Basically, it comes down to how much physical area 13 13 00:00:24,070 --> 00:00:26,160 you can use with your wireless devices 14 14 00:00:26,160 --> 00:00:28,060 before you get outside the coverage area 15 15 00:00:28,060 --> 00:00:29,420 and you lose signal. 16 16 00:00:29,420 --> 00:00:30,860 To determine your coverage area, 17 17 00:00:30,860 --> 00:00:33,230 you're going to conduct a wireless site survey. 18 18 00:00:33,230 --> 00:00:35,070 This'll generate a heat map showing the areas 19 19 00:00:35,070 --> 00:00:36,870 with the highest level signals in green, 20 20 00:00:36,870 --> 00:00:39,210 then as they get weaker, it goes to yellow, 21 21 00:00:39,210 --> 00:00:41,650 orange and red with the weakest signals. 22 22 00:00:41,650 --> 00:00:44,250 Now, the signal is always getting measured from your client, 23 23 00:00:44,250 --> 00:00:45,900 using the RSSI. 24 24 00:00:45,900 --> 00:00:47,700 And this is measured in decibels. 25 25 00:00:47,700 --> 00:00:49,800 If you're going to measure it from your access point, 26 26 00:00:49,800 --> 00:00:51,890 you're going to measure it in EIRP 27 27 00:00:51,890 --> 00:00:54,040 and you're going to do that in dBI. 28 28 00:00:54,040 --> 00:00:56,020 Now, one of the most common issues experienced 29 29 00:00:56,020 --> 00:00:59,270 by Wi-Fi users is insufficient wireless coverage. 30 30 00:00:59,270 --> 00:01:01,720 For example, let's say you have a three-story townhouse 31 31 00:01:01,720 --> 00:01:03,820 and you only have a single wireless access point 32 32 00:01:03,820 --> 00:01:05,520 on the main floor of that home. 33 33 00:01:05,520 --> 00:01:07,310 Well, it's going to be unlikely to provide you 34 34 00:01:07,310 --> 00:01:08,930 with sufficient coverage all the way up 35 35 00:01:08,930 --> 00:01:11,110 on the third story of your townhouse. 36 36 00:01:11,110 --> 00:01:13,030 In this case, if you're using your laptop 37 37 00:01:13,030 --> 00:01:15,670 on the first floor, everything's going to work just fine 38 38 00:01:15,670 --> 00:01:18,080 because you have really high RSSI value. 39 39 00:01:18,080 --> 00:01:19,900 But when you go up to the second floor, 40 40 00:01:19,900 --> 00:01:22,070 that RSSI value is going to lower 41 41 00:01:22,070 --> 00:01:24,640 because the signal got weaker as you got further away, 42 42 00:01:24,640 --> 00:01:26,370 and the signal has to now go through the ceiling 43 43 00:01:26,370 --> 00:01:27,850 of the first floor to get into 44 44 00:01:27,850 --> 00:01:29,500 that second floor you're sitting at. 45 45 00:01:29,500 --> 00:01:31,660 Now, if you go up another level to the third floor, 46 46 00:01:31,660 --> 00:01:34,350 that signal may be too weak to even register 47 47 00:01:34,350 --> 00:01:37,690 by your wireless client, or it can drop you completely. 48 48 00:01:37,690 --> 00:01:39,960 Now, if this happens, you're going to need to find a way 49 49 00:01:39,960 --> 00:01:42,430 to boost up that signal and make it stronger 50 50 00:01:42,430 --> 00:01:44,400 so you can increase your coverage area. 51 51 00:01:44,400 --> 00:01:47,300 To do this, you can use a signal booster to raise the power, 52 52 00:01:47,300 --> 00:01:49,700 you can use an antenna with a stronger DB rating, 53 53 00:01:49,700 --> 00:01:51,230 you can use a wireless repeater, 54 54 00:01:51,230 --> 00:01:53,600 or you can add a second wireless access point 55 55 00:01:53,600 --> 00:01:55,670 that can operate in an extended server set 56 56 00:01:55,670 --> 00:01:58,810 or ESS configuration with your initial access point. 57 57 00:01:58,810 --> 00:02:00,700 Remember, the coverage area for a single 58 58 00:02:00,700 --> 00:02:03,950 wireless access point is affected by two main factors, 59 59 00:02:03,950 --> 00:02:06,170 the amount of power that the transmitter is sending out, 60 60 00:02:06,170 --> 00:02:07,820 and the size of your antenna. 61 61 00:02:07,820 --> 00:02:09,490 If you replace a five decibel antenna 62 62 00:02:09,490 --> 00:02:10,960 with a nine decibel antenna, 63 63 00:02:10,960 --> 00:02:12,640 you're going to effectively double your range 64 64 00:02:12,640 --> 00:02:14,110 under the right conditions. 65 65 00:02:14,110 --> 00:02:15,610 As for the power being sent out 66 66 00:02:15,610 --> 00:02:17,470 unfortunately, you're normally going to be limited 67 67 00:02:17,470 --> 00:02:18,870 in your ability to control that 68 68 00:02:18,870 --> 00:02:20,590 because there's a maximum amount of power 69 69 00:02:20,590 --> 00:02:23,300 that the FCC and regulators allow us to use 70 70 00:02:23,300 --> 00:02:25,620 inside of the wireless frequency range, 71 71 00:02:25,620 --> 00:02:28,420 but you could use a wireless repeater. 72 72 00:02:28,420 --> 00:02:31,320 Now, a wireless repeater is simply a layer one device 73 73 00:02:31,320 --> 00:02:33,180 that has two radios built into it. 74 74 00:02:33,180 --> 00:02:34,920 You plug this device into a power outlet 75 75 00:02:34,920 --> 00:02:37,190 and you configure it to connect to your wireless network. 76 76 00:02:37,190 --> 00:02:39,300 Now, one of the radios grabs the signal 77 77 00:02:39,300 --> 00:02:40,690 from your wireless network. 78 78 00:02:40,690 --> 00:02:42,390 Then it's going to boost up the signal 79 79 00:02:42,390 --> 00:02:45,130 and send it out again off its other radio. 80 80 00:02:45,130 --> 00:02:46,590 This way, when the signal comes in 81 81 00:02:46,590 --> 00:02:48,830 on one side of the device, it's going to be repeated out 82 82 00:02:48,830 --> 00:02:51,210 at full strength on the other radio too. 83 83 00:02:51,210 --> 00:02:53,110 This will extend that wireless network 84 84 00:02:53,110 --> 00:02:54,960 into an additional area of space 85 85 00:02:54,960 --> 00:02:56,900 because you have this new signal going out 86 86 00:02:56,900 --> 00:02:58,430 from this repeater. 87 87 00:02:58,430 --> 00:03:00,240 For example, let's say if this repeater 88 88 00:03:00,240 --> 00:03:03,190 receives a signal at -70 RSSI. 89 89 00:03:03,190 --> 00:03:05,220 It can retransmit it to get it out on the other side 90 90 00:03:05,220 --> 00:03:07,150 at -30 RSSI. 91 91 00:03:07,150 --> 00:03:09,780 Effectively making it a brand new signal. 92 92 00:03:09,780 --> 00:03:12,500 So, in the example of a three-story townhouse, 93 93 00:03:12,500 --> 00:03:14,770 I might want to have my first wireless access point 94 94 00:03:14,770 --> 00:03:16,060 on the first floor. 95 95 00:03:16,060 --> 00:03:18,730 Then I can have a repeater on the second floor. 96 96 00:03:18,730 --> 00:03:19,730 Now, at this point, 97 97 00:03:19,730 --> 00:03:22,060 we'll probably have some signal on the third floor, 98 98 00:03:22,060 --> 00:03:24,660 or we could put another repeater on the third floor 99 99 00:03:24,660 --> 00:03:26,360 to boost that signal even more 100 100 00:03:26,360 --> 00:03:28,530 when it reaches it from the second floor. 101 101 00:03:28,530 --> 00:03:30,960 Finally, we could use an extended server set 102 102 00:03:30,960 --> 00:03:33,140 to cover the entire building properly. 103 103 00:03:33,140 --> 00:03:34,380 In one of my old houses, 104 104 00:03:34,380 --> 00:03:36,460 I actually ran ethernet twisted pair cable 105 105 00:03:36,460 --> 00:03:38,800 from the basement to the second floor of my house, 106 106 00:03:38,800 --> 00:03:41,600 and then I connected a second wireless access point there. 107 107 00:03:41,600 --> 00:03:44,140 These two wireless access points work together 108 108 00:03:44,140 --> 00:03:46,090 to provide coverage over the entire home. 109 109 00:03:46,090 --> 00:03:48,190 One from the top down from the second floor, 110 110 00:03:48,190 --> 00:03:50,340 and one from the bottom up going from the basement. 111 111 00:03:50,340 --> 00:03:52,800 And this gave me adequate coverage for the whole house. 112 112 00:03:52,800 --> 00:03:54,260 Now, each wireless access point 113 113 00:03:54,260 --> 00:03:55,480 operate on a different channel 114 114 00:03:55,480 --> 00:03:57,510 and I could run from upstairs to downstairs 115 115 00:03:57,510 --> 00:03:59,160 and my devices would automatically switch 116 116 00:03:59,160 --> 00:04:00,690 from one access point to the other 117 117 00:04:00,690 --> 00:04:02,950 as they needed to, to maintain coverage. 118 118 00:04:02,950 --> 00:04:05,830 These days, we also have wireless mesh systems available. 119 119 00:04:05,830 --> 00:04:07,610 And they rely on a combination of repeaters 120 120 00:04:07,610 --> 00:04:10,110 and access points that are put into a single device 121 121 00:04:10,110 --> 00:04:12,820 to provide full coverage for larger homes and offices. 122 122 00:04:12,820 --> 00:04:15,130 Instead of having to run ethernet cables to each device, 123 123 00:04:15,130 --> 00:04:17,360 they instead rely on internal wireless radios 124 124 00:04:17,360 --> 00:04:19,600 to send the data from one device to the other 125 125 00:04:19,600 --> 00:04:21,350 and create a whole house mesh network 126 126 00:04:21,350 --> 00:04:24,270 for the wireless network with sufficient coverage. 127 127 00:04:24,270 --> 00:04:26,410 Next, let's talk about interference. 128 128 00:04:26,410 --> 00:04:28,930 If you remember, anytime you have multiple wireless networks 129 129 00:04:28,930 --> 00:04:30,400 communicating on the same channel, 130 130 00:04:30,400 --> 00:04:31,540 you can have interference 131 131 00:04:31,540 --> 00:04:34,240 because they're all talking at the same frequency. 132 132 00:04:34,240 --> 00:04:36,930 To avoid interference in the 2.4 gigahertz spectrum, 133 133 00:04:36,930 --> 00:04:40,830 we always use the three channels of one, six, and 11. 134 134 00:04:40,830 --> 00:04:42,090 If I'm using channel six 135 135 00:04:42,090 --> 00:04:43,640 and you're using channel four though, 136 136 00:04:43,640 --> 00:04:44,780 we're going to have an overlap 137 137 00:04:44,780 --> 00:04:46,900 and we're going to interfere with each other's networks. 138 138 00:04:46,900 --> 00:04:48,620 This interference can lead to retransmissions 139 139 00:04:48,620 --> 00:04:51,340 and this will slow down both of our networks. 140 140 00:04:51,340 --> 00:04:53,520 So when you're conducting your site survey, 141 141 00:04:53,520 --> 00:04:55,070 you're always going to want to make sure you see 142 142 00:04:55,070 --> 00:04:56,280 what channels and frequencies 143 143 00:04:56,280 --> 00:04:58,200 are already being used in your area. 144 144 00:04:58,200 --> 00:05:00,630 If you create an extended service at wireless network, 145 145 00:05:00,630 --> 00:05:02,940 you need to plan the locations of your access points 146 146 00:05:02,940 --> 00:05:04,600 and the channels they are going to use. 147 147 00:05:04,600 --> 00:05:06,890 Remember, in a 2.4 gigahertz network, 148 148 00:05:06,890 --> 00:05:08,270 you always want to make sure you're using 149 149 00:05:08,270 --> 00:05:10,150 channels one, six, and 11, 150 150 00:05:10,150 --> 00:05:12,260 and you never want to have the same channel number 151 151 00:05:12,260 --> 00:05:14,540 sitting next to each other and overlapping. 152 152 00:05:14,540 --> 00:05:17,410 This way, I can make sure that I have good coverage. 153 153 00:05:17,410 --> 00:05:19,730 For example, let's say I was installing access points 154 154 00:05:19,730 --> 00:05:20,940 down a long hallway. 155 155 00:05:20,940 --> 00:05:25,550 I would install them as one, six, 11, one, six, and 11. 156 156 00:05:25,550 --> 00:05:28,360 Notice that I skipped each one to a different number. 157 157 00:05:28,360 --> 00:05:30,360 This ensures there's no overlapping zones, 158 158 00:05:30,360 --> 00:05:33,120 they're touching one another of the same type of number. 159 159 00:05:33,120 --> 00:05:36,260 Also, you want to ensure you have 10 to 15% overlap 160 160 00:05:36,260 --> 00:05:37,870 between the two access points 161 161 00:05:37,870 --> 00:05:39,380 to make sure you have sufficient coverage 162 162 00:05:39,380 --> 00:05:41,620 and time for the devices to hand off. 163 163 00:05:41,620 --> 00:05:44,020 Now, if you're using a newer five gigahertz network, 164 164 00:05:44,020 --> 00:05:45,810 you're going to utilize a honeycomb pattern 165 165 00:05:45,810 --> 00:05:48,040 for your access points as they're being installed. 166 166 00:05:48,040 --> 00:05:49,920 And you should always ensure that each channel 167 167 00:05:49,920 --> 00:05:52,700 is not repeated until you're at least two zones away. 168 168 00:05:52,700 --> 00:05:55,660 This'll ensure adequate coverage and minimize interference. 169 169 00:05:55,660 --> 00:05:57,870 Next, let's cover attenuation. 170 170 00:05:57,870 --> 00:06:00,020 Attenuation is a reduction in signal strength 171 171 00:06:00,020 --> 00:06:02,860 between the transmission and receipt of the wireless signal. 172 172 00:06:02,860 --> 00:06:05,500 Attenuation can occur for lots of different reasons, 173 173 00:06:05,500 --> 00:06:06,610 such as increase in the distance 174 174 00:06:06,610 --> 00:06:08,250 between the transmitter and the receiver, 175 175 00:06:08,250 --> 00:06:10,360 hitting a wall or other physical obstacle, 176 176 00:06:10,360 --> 00:06:12,350 or signal interference that's reducing 177 177 00:06:12,350 --> 00:06:13,600 the overall signal strength 178 178 00:06:13,600 --> 00:06:15,220 because of more noise in the environment 179 179 00:06:15,220 --> 00:06:16,490 causing interference. 180 180 00:06:16,490 --> 00:06:19,190 Attenuation can occur within the antenna's cable itself 181 181 00:06:19,190 --> 00:06:20,960 or in the radio frequency wave 182 182 00:06:20,960 --> 00:06:22,620 as it's traveling away from the transmitter 183 183 00:06:22,620 --> 00:06:24,090 and towards the receiver. 184 184 00:06:24,090 --> 00:06:25,550 When the attenuation is occurring 185 185 00:06:25,550 --> 00:06:28,050 inside the antenna's cable, it's normally going to be caused 186 186 00:06:28,050 --> 00:06:30,690 by the materials and the construction of that antenna. 187 187 00:06:30,690 --> 00:06:33,240 If low quality components were used to make that antenna 188 188 00:06:33,240 --> 00:06:34,750 or the cables inside of it, 189 189 00:06:34,750 --> 00:06:37,400 there are going to be more resistance inside that wire, 190 190 00:06:37,400 --> 00:06:39,490 and that leads to more attenuation. 191 191 00:06:39,490 --> 00:06:42,130 To increase the signal strength and reduce the attenuation, 192 192 00:06:42,130 --> 00:06:44,200 you can replace the cable or the antenna 193 193 00:06:44,200 --> 00:06:47,000 with a higher quality, lower resistant component. 194 194 00:06:47,000 --> 00:06:49,380 With radio-frequency wave signal attenuation, 195 195 00:06:49,380 --> 00:06:52,410 one of the causes of this is multipath reception. 196 196 00:06:52,410 --> 00:06:54,340 Now, this occurs when the transmitted signal 197 197 00:06:54,340 --> 00:06:56,930 starts bouncing off walls and other physical objects, 198 198 00:06:56,930 --> 00:07:00,240 and then it eventually gets redirected back to the receiver. 199 199 00:07:00,240 --> 00:07:01,840 Now, for example, let's say I was standing 200 200 00:07:01,840 --> 00:07:02,840 on one side of the room 201 201 00:07:02,840 --> 00:07:04,530 and you're standing on the other side of the room. 202 202 00:07:04,530 --> 00:07:07,280 And there's a big support column standing right between us. 203 203 00:07:07,280 --> 00:07:08,540 If I wanted to send a ball to you 204 204 00:07:08,540 --> 00:07:10,480 that's going to signify my radio waves, 205 205 00:07:10,480 --> 00:07:12,160 I couldn't throw it directly to you. 206 206 00:07:12,160 --> 00:07:13,170 Because if I did that, 207 207 00:07:13,170 --> 00:07:15,670 it's going to hit the column and bounce back towards me. 208 208 00:07:15,670 --> 00:07:19,030 So instead, I would need as an omnidirectional antenna 209 209 00:07:19,030 --> 00:07:21,410 to throw out a lot of different balls simultaneously. 210 210 00:07:21,410 --> 00:07:22,980 Some of those will bounce off the sidewalls 211 211 00:07:22,980 --> 00:07:24,230 and they'll eventually reach you. 212 212 00:07:24,230 --> 00:07:26,910 Some will hit the pole in front of me and bounce back to me. 213 213 00:07:26,910 --> 00:07:28,970 But, because of all this different bounce, 214 214 00:07:28,970 --> 00:07:30,980 we're going to have slower and weaker signals 215 215 00:07:30,980 --> 00:07:32,420 by the time they get to you, 216 216 00:07:32,420 --> 00:07:34,740 because I had to bounce off the wall first, right? 217 217 00:07:34,740 --> 00:07:37,470 Well, the same thing happens with our radio frequency waves. 218 218 00:07:37,470 --> 00:07:38,800 They may bounce around the room 219 219 00:07:38,800 --> 00:07:40,030 and they'll eventually get to you, 220 220 00:07:40,030 --> 00:07:42,930 but they may be attenuated and weaker than before 221 221 00:07:42,930 --> 00:07:45,810 and it's going to lead to a lower RSSI value for you 222 222 00:07:45,810 --> 00:07:47,250 and lower throughput for the data 223 223 00:07:47,250 --> 00:07:49,070 being sent over these networks. 224 224 00:07:49,070 --> 00:07:52,390 Now, finally, we need to talk about disassociation issues 225 225 00:07:52,390 --> 00:07:54,060 within our wireless networks. 226 226 00:07:54,060 --> 00:07:55,580 There's a lot of reasons that a client 227 227 00:07:55,580 --> 00:07:58,080 would be disassociated from a wireless access point. 228 228 00:07:58,080 --> 00:08:00,820 This includes an idle timeout, a session timeout, 229 229 00:08:00,820 --> 00:08:03,390 wireless network changes, manual deletion, 230 230 00:08:03,390 --> 00:08:06,740 authentication timeouts, or access point radio resets. 231 231 00:08:06,740 --> 00:08:09,390 Now, a client association due to an idle timeout 232 232 00:08:09,390 --> 00:08:11,170 is going to occur whenever a wireless client 233 233 00:08:11,170 --> 00:08:14,310 doesn't send or receive traffic within 300 seconds, 234 234 00:08:14,310 --> 00:08:15,730 which is five minutes. 235 235 00:08:15,730 --> 00:08:18,450 This is the default setting on most wireless access points, 236 236 00:08:18,450 --> 00:08:19,700 and it's used to free up the network 237 237 00:08:19,700 --> 00:08:21,270 for other clients to join. 238 238 00:08:21,270 --> 00:08:22,570 To prevent this from occurring, 239 239 00:08:22,570 --> 00:08:24,400 some wireless client implementations 240 240 00:08:24,400 --> 00:08:27,080 will send out a keep alive packet every few minutes 241 241 00:08:27,080 --> 00:08:28,810 so they can remain connected the entire time 242 242 00:08:28,810 --> 00:08:30,290 to that wireless network. 243 243 00:08:30,290 --> 00:08:32,130 Now, a client association can also occur 244 244 00:08:32,130 --> 00:08:33,480 due to a session timeout, 245 245 00:08:33,480 --> 00:08:36,190 and this will happen after 1800 seconds. 246 246 00:08:36,190 --> 00:08:37,810 At this point, the wireless client 247 247 00:08:37,810 --> 00:08:39,860 should reconduct an authentication again 248 248 00:08:39,860 --> 00:08:42,260 and reestablish their connection automatically. 249 249 00:08:42,260 --> 00:08:43,480 This again is something that's handled 250 250 00:08:43,480 --> 00:08:45,980 by your wireless client automatically on your behalf 251 251 00:08:45,980 --> 00:08:48,620 in coordination with the wireless access point. 252 252 00:08:48,620 --> 00:08:49,990 Next, we have client disassociations 253 253 00:08:49,990 --> 00:08:52,500 that occur due to wireless network changes. 254 254 00:08:52,500 --> 00:08:54,760 And this occurs whenever the wireless local area network 255 255 00:08:54,760 --> 00:08:56,410 is being changed and this change 256 256 00:08:56,410 --> 00:08:58,590 causes the wireless network to be disabled 257 257 00:08:58,590 --> 00:09:00,340 and then reenable itself. 258 258 00:09:00,340 --> 00:09:02,960 For example, if you're going to change the shared pass phrase 259 259 00:09:02,960 --> 00:09:04,140 that secures the network, 260 260 00:09:04,140 --> 00:09:05,870 it's going to reboot the wireless network 261 261 00:09:05,870 --> 00:09:09,070 and force every device to reconnect and reauthenticate. 262 262 00:09:09,070 --> 00:09:10,870 This makes a lot of sense because we want to make sure 263 263 00:09:10,870 --> 00:09:13,200 they all have the right password again, right? 264 264 00:09:13,200 --> 00:09:15,040 Another client association we can have 265 265 00:09:15,040 --> 00:09:16,850 is caused by manual deletion. 266 266 00:09:16,850 --> 00:09:18,510 And this occurs whenever a wireless client 267 267 00:09:18,510 --> 00:09:20,090 is removed by an administrator. 268 268 00:09:20,090 --> 00:09:22,250 This makes sense because if I kicked your client 269 269 00:09:22,250 --> 00:09:24,620 off my network, that means I want you to be dissociate 270 270 00:09:24,620 --> 00:09:27,404 and removed, and then you'd have to reconnect again. 271 271 00:09:27,404 --> 00:09:30,000 Now, another way that client associations occur 272 272 00:09:30,000 --> 00:09:31,920 is due to authentication timeouts. 273 273 00:09:31,920 --> 00:09:33,620 And this occurs whenever the authentication 274 274 00:09:33,620 --> 00:09:36,930 or key exchange process fails to finish in a given time. 275 275 00:09:36,930 --> 00:09:38,600 When this occurs, the wireless client 276 276 00:09:38,600 --> 00:09:40,280 is disassociated from the access point 277 277 00:09:40,280 --> 00:09:42,290 and needs to restart the authentication process 278 278 00:09:42,290 --> 00:09:45,210 all over again to regain access. 279 279 00:09:45,210 --> 00:09:47,670 Another time you'll find client disassociations occurring 280 280 00:09:47,670 --> 00:09:49,880 is when your access point radio is reset. 281 281 00:09:49,880 --> 00:09:51,240 And this is similar to the change 282 282 00:09:51,240 --> 00:09:52,980 that we made with the wireless network. 283 283 00:09:52,980 --> 00:09:55,010 All of our clients are going to be disassociated, 284 284 00:09:55,010 --> 00:09:56,970 the radio is going to be turned off and turned on 285 285 00:09:56,970 --> 00:09:59,050 to cause that reset, and then the clients 286 286 00:09:59,050 --> 00:10:01,610 can begin their association process once more. 287 287 00:10:01,610 --> 00:10:04,260 Now, why is it important to understand all these times 288 288 00:10:04,260 --> 00:10:06,000 when disassociation happens? 289 289 00:10:06,000 --> 00:10:08,820 Well, because sometimes your clients can be disassociated 290 290 00:10:08,820 --> 00:10:10,570 as part of a deauthentication attack 291 291 00:10:10,570 --> 00:10:13,120 and not for one of these real legitimate reasons. 292 292 00:10:13,120 --> 00:10:15,810 This is a common wireless attack that is used by hackers 293 293 00:10:15,810 --> 00:10:17,890 to disassociate your wireless clients 294 294 00:10:17,890 --> 00:10:20,370 and make them attempt to reconnect to the access point. 295 295 00:10:20,370 --> 00:10:21,490 Now, when this occurs, 296 296 00:10:21,490 --> 00:10:23,050 the attacker is going to attempt to capture 297 297 00:10:23,050 --> 00:10:24,927 the packet's use in the association 298 298 00:10:24,927 --> 00:10:26,433 and authentication processes, 299 299 00:10:26,433 --> 00:10:28,950 and then they'll try to crack that shared pass phrase 300 300 00:10:28,950 --> 00:10:31,300 to gain access to the network indefinitely. 301 301 00:10:31,300 --> 00:10:32,860 So if you see a client 302 302 00:10:32,860 --> 00:10:34,810 that's continually being deauthenticated, 303 303 00:10:34,810 --> 00:10:36,630 you need to check your wireless gateways 304 304 00:10:36,630 --> 00:10:38,000 and your wireless controller logs 305 305 00:10:38,000 --> 00:10:39,610 to determine the root cause. 306 306 00:10:39,610 --> 00:10:41,720 It could be one of the ones I just mentioned above, 307 307 00:10:41,720 --> 00:10:43,870 and all of those are normal and expected. 308 308 00:10:43,870 --> 00:10:45,070 But if it's not one of those, 309 309 00:10:45,070 --> 00:10:46,670 it could be caused by an attacker. 310 310 00:10:46,670 --> 00:10:49,063 And that's something you need to investigate further.