1 00:00:00,120 --> 00:00:01,750 In this lesson, 2 00:00:01,750 --> 00:00:02,940 we're going to talk about interface statistics 3 00:00:02,940 --> 00:00:03,773 and how it's used 4 00:00:03,773 --> 00:00:05,700 to monitor our network's performance. 5 00:00:05,700 --> 00:00:08,100 Now, if you're new to networking, you may be wondering 6 00:00:08,100 --> 00:00:10,230 what exactly is an interface? 7 00:00:10,230 --> 00:00:12,300 Well, an interface is just one of the physical 8 00:00:12,300 --> 00:00:14,880 or logical switch ports on a router, switch 9 00:00:14,880 --> 00:00:17,370 or firewall, enterprise level devices, 10 00:00:17,370 --> 00:00:19,670 each interface can generate its own statistics 11 00:00:20,680 --> 00:00:21,690 and maintains its own status. 12 00:00:21,690 --> 00:00:24,330 In this lesson, we're going to explore the link state, 13 00:00:24,330 --> 00:00:26,040 the speed and duplex status, 14 00:00:26,040 --> 00:00:28,170 the send receive traffic statistics, 15 00:00:28,170 --> 00:00:30,300 the cyclic redundancy check statistics, 16 00:00:30,300 --> 00:00:31,410 and the protocol packet 17 00:00:31,410 --> 00:00:34,440 and byte counts that are collected for our network devices. 18 00:00:34,440 --> 00:00:35,730 To help guide our discussions, 19 00:00:35,730 --> 00:00:37,860 I'm going to be using the output from a Cisco router 20 00:00:37,860 --> 00:00:40,710 for an interface called F0/0, 21 00:00:40,710 --> 00:00:42,810 which simply means it's a fast ethernet 22 00:00:42,810 --> 00:00:45,810 or CAT5 connection going from this physical interface 23 00:00:45,810 --> 00:00:49,140 on slot zero and port zero of a given router. 24 00:00:49,140 --> 00:00:51,720 Now first, you can see we have the link state. 25 00:00:51,720 --> 00:00:53,250 A link state is used to communicate 26 00:00:53,250 --> 00:00:56,250 whether or not a given interface has a cable connected to it 27 00:00:56,250 --> 00:00:58,770 and a valid protocol to use for communication. 28 00:00:58,770 --> 00:01:01,200 For example, if I connected a fast ethernet 29 00:01:01,200 --> 00:01:02,490 unshielded twisted pair cable 30 00:01:02,490 --> 00:01:04,379 to the interface on 0/0 31 00:01:04,379 --> 00:01:06,540 of this router and then plugged in the other end 32 00:01:06,540 --> 00:01:08,850 into another router to create a connection, 33 00:01:08,850 --> 00:01:11,940 I should see fast ethernet 0/0 is up 34 00:01:11,940 --> 00:01:13,830 line protocol is up. 35 00:01:13,830 --> 00:01:16,470 This indicates that the interface is physically up 36 00:01:16,470 --> 00:01:18,960 and the protocol is operational. 37 00:01:18,960 --> 00:01:21,330 If we're using ethernet, that means that frames 38 00:01:21,330 --> 00:01:24,210 are able to be entering and leaving this interface. 39 00:01:24,210 --> 00:01:27,060 Next, we have some information about the interface itself, 40 00:01:27,060 --> 00:01:30,090 such as the MAC address and the IP address assigned to it. 41 00:01:30,090 --> 00:01:33,810 After that, we see there's an MTU size set of 1500 bytes, 42 00:01:33,810 --> 00:01:36,090 which is normally used by default in ethernet, 43 00:01:36,090 --> 00:01:39,120 and then we have the bandwidth is being set at 100,000 44 00:01:39,120 --> 00:01:43,080 kilobits per second, which is 100 megabits per second. 45 00:01:43,080 --> 00:01:45,480 This makes sense because I'm using fast ethernet 46 00:01:45,480 --> 00:01:48,090 or CAT5 cabling for our connection. 47 00:01:48,090 --> 00:01:49,890 This speed is also used by the router, 48 00:01:49,890 --> 00:01:51,360 which is trying to calculate the metrics 49 00:01:51,360 --> 00:01:54,990 for the routing protocols like OSPF and EIGRP, 50 00:01:54,990 --> 00:01:56,640 since they rely on the connection speed 51 00:01:56,640 --> 00:01:59,670 in making their determinations and their link costs. 52 00:01:59,670 --> 00:02:02,520 Next we have the reliability, which is being shown here 53 00:02:02,520 --> 00:02:05,220 as 255 out of 255. 54 00:02:05,220 --> 00:02:07,650 This means if the connection begins to have more inputs 55 00:02:07,650 --> 00:02:10,770 or output errors, you're going to see the reliability lower. 56 00:02:10,770 --> 00:02:13,140 Basically, you read this as reliability 57 00:02:13,140 --> 00:02:14,730 equals the number of packets 58 00:02:14,730 --> 00:02:16,710 divided by the total number of frames, 59 00:02:16,710 --> 00:02:20,280 so 255 over 255 is the best reliability, 60 00:02:20,280 --> 00:02:21,900 and it indicates there is no packets 61 00:02:21,900 --> 00:02:24,180 or frames that have been dropped so far. 62 00:02:24,180 --> 00:02:26,130 TX load is our next statistic, 63 00:02:26,130 --> 00:02:27,240 and this is going to indicate 64 00:02:27,240 --> 00:02:29,400 how busy the router is transmitting frames 65 00:02:29,400 --> 00:02:30,660 over this connection. 66 00:02:30,660 --> 00:02:34,650 At one out of 255, this router is not very busy at all. 67 00:02:34,650 --> 00:02:36,510 Rxload is like Txload, 68 00:02:36,510 --> 00:02:38,670 but instead of transmitting, we're going to be measuring 69 00:02:38,670 --> 00:02:41,970 how busy the router is in terms of receiving frames. 70 00:02:41,970 --> 00:02:44,370 Next, we have the ARC type being used. 71 00:02:44,370 --> 00:02:46,860 In this case, we're using ARPA 72 00:02:46,860 --> 00:02:49,440 or the advanced research project agency setting, 73 00:02:49,440 --> 00:02:51,900 which indicates that we're using standard ethernet. 74 00:02:51,900 --> 00:02:53,652 This is because ARPA developed standard ethernet 75 00:02:53,652 --> 00:02:56,160 and we're using that for ethernet frames 76 00:02:56,160 --> 00:02:57,630 for our encapsulation. 77 00:02:57,630 --> 00:03:00,060 Now, if you're using something different, a serial link 78 00:03:00,060 --> 00:03:02,460 or a frame relay, it would say something different here 79 00:03:02,460 --> 00:03:05,040 instead of ARPA, but if you're using ethernet, 80 00:03:05,040 --> 00:03:07,350 you should expect to see ARPA right here. 81 00:03:07,350 --> 00:03:09,000 Next we have the keep alive, 82 00:03:09,000 --> 00:03:11,790 and this is set to 10 seconds, which is the default. 83 00:03:11,790 --> 00:03:12,990 This is how often the router 84 00:03:12,990 --> 00:03:14,520 is going to send a keep alive packet 85 00:03:14,520 --> 00:03:16,320 to other devices that is connected to 86 00:03:16,320 --> 00:03:18,390 to check if they're still up and online. 87 00:03:18,390 --> 00:03:20,640 Next, we have a line that says, full duplex, 88 00:03:20,640 --> 00:03:24,690 100 megabits per second, 100BaseTX/FX. 89 00:03:24,690 --> 00:03:27,420 Now, this indicates whether this interface is using half 90 00:03:27,420 --> 00:03:30,690 or full duplex, and in this case we're using full duplex. 91 00:03:30,690 --> 00:03:32,370 It also tells you what the bandwidth 92 00:03:32,370 --> 00:03:34,620 is and the interface type you're using. 93 00:03:34,620 --> 00:03:37,290 In this case, as I said, we're using full duplex 94 00:03:37,290 --> 00:03:40,080 and we're using 100 megabits per second as our bandwidth, 95 00:03:40,080 --> 00:03:41,592 and we have a fast ethernet interface type 96 00:03:41,592 --> 00:03:44,490 and it's either using copper or fiber cabling 97 00:03:44,490 --> 00:03:47,130 because it says TX/FX. 98 00:03:47,130 --> 00:03:49,290 Now, next we're going to have our ARP type, 99 00:03:49,290 --> 00:03:51,990 and in this case again, we're going to use ARPA. 100 00:03:51,990 --> 00:03:53,070 The timeout here tells us 101 00:03:53,070 --> 00:03:56,070 how long each ARP cache is going to remember a binding 102 00:03:56,070 --> 00:03:57,390 and when it will be cleared. 103 00:03:57,390 --> 00:03:59,972 In this case, we're using the default time of four hours. 104 00:03:59,972 --> 00:04:03,750 The next two lines are the last input, last output, 105 00:04:03,750 --> 00:04:05,580 and last clearing of the counters. 106 00:04:05,580 --> 00:04:07,890 In this case, the router was just rebooted, 107 00:04:07,890 --> 00:04:09,420 so they're all set to zero 108 00:04:09,420 --> 00:04:11,250 because they were all just cleared. 109 00:04:11,250 --> 00:04:13,350 Next, we have our input queue, which tells us 110 00:04:13,350 --> 00:04:15,210 how many packets are in the input queue 111 00:04:15,210 --> 00:04:16,829 and their maximum size. 112 00:04:16,829 --> 00:04:19,680 In this case, the maximum size is 75 packets 113 00:04:19,680 --> 00:04:22,050 For our queue, drops is the number of packets 114 00:04:22,050 --> 00:04:23,430 that have been dropped so far. 115 00:04:23,430 --> 00:04:26,070 Flushes is used to count the selective packet discards 116 00:04:26,070 --> 00:04:26,910 that have occurred. 117 00:04:26,910 --> 00:04:28,350 Basically, when the router 118 00:04:28,350 --> 00:04:31,620 or switch has to say it needs to start shedding some load 119 00:04:31,620 --> 00:04:34,170 and it starts dropping packets selectively, 120 00:04:34,170 --> 00:04:35,400 SPD is a protocol 121 00:04:35,400 --> 00:04:38,070 that's going to drop your lowest priority packets when the CPU 122 00:04:38,070 --> 00:04:40,650 becomes too busy, so that way it can save capacity 123 00:04:40,650 --> 00:04:44,070 for higher priority packets as a form of quality of service. 124 00:04:44,070 --> 00:04:46,920 Now, the total output drops here is at zero. 125 00:04:46,920 --> 00:04:48,540 This means that we've had no drops 126 00:04:48,540 --> 00:04:51,030 because we never had a full output queue. 127 00:04:51,030 --> 00:04:53,250 Since we have 100 megabit per second connection, 128 00:04:53,250 --> 00:04:54,240 as long as we're communicating 129 00:04:54,240 --> 00:04:56,520 with another 100 megabit per second connection, 130 00:04:56,520 --> 00:04:59,280 we should see this stay at zero drop packets. 131 00:04:59,280 --> 00:05:01,710 If we started using a 20 megabit per second connection, 132 00:05:01,710 --> 00:05:03,240 for instance on our ISP, 133 00:05:03,240 --> 00:05:05,370 then we might likely have an experience here 134 00:05:05,370 --> 00:05:08,220 with network congestion because we're sending it 100, 135 00:05:08,220 --> 00:05:10,350 but they can only take it at 20. 136 00:05:10,350 --> 00:05:11,820 That would cause a problem for us, 137 00:05:11,820 --> 00:05:14,610 and at that point, some of our packets might get dropped. 138 00:05:14,610 --> 00:05:16,230 Next, we have our queuing strategy 139 00:05:16,230 --> 00:05:17,640 for our quality of service. 140 00:05:17,640 --> 00:05:21,000 In this case, we're setting this as first in, first out, 141 00:05:21,000 --> 00:05:22,740 which is known as FIFO. 142 00:05:22,740 --> 00:05:25,110 This is the default for this type of router. 143 00:05:25,110 --> 00:05:28,290 Next, we have output queue size and the maximum. 144 00:05:28,290 --> 00:05:31,560 Currently, our queue is empty and it's showing zero packets. 145 00:05:31,560 --> 00:05:34,380 Now the maximum queue size here is set at 40, 146 00:05:34,380 --> 00:05:36,660 so if I receive more than 40 packets, 147 00:05:36,660 --> 00:05:38,370 the queue is not going to be able to hold it 148 00:05:38,370 --> 00:05:40,770 and the rest of those will get dropped. 149 00:05:40,770 --> 00:05:43,770 Next, we have our minute input and output rates. 150 00:05:43,770 --> 00:05:45,840 Now here are the average rates at which packets 151 00:05:45,840 --> 00:05:48,360 are being received and being transmitted. 152 00:05:48,360 --> 00:05:50,250 Packet input is our next line, 153 00:05:50,250 --> 00:05:53,100 and here we can see 923 packet inputs 154 00:05:53,100 --> 00:05:55,830 was received for a total of 158866 155 00:05:55,830 --> 00:05:59,490 158866 bytes of data being processed. 156 00:05:59,490 --> 00:06:01,740 The next line contains the receive broadcast, 157 00:06:01,740 --> 00:06:05,160 and in this case we received 860 broadcast frames. 158 00:06:05,160 --> 00:06:06,780 We also have runts, giants 159 00:06:06,780 --> 00:06:08,640 and throttles counted here as well. 160 00:06:08,640 --> 00:06:10,500 Now, a runt is an ethernet frame 161 00:06:10,500 --> 00:06:12,690 that is less than 64 bytes in size. 162 00:06:12,690 --> 00:06:15,150 It's really small, that's why it's a runt. 163 00:06:15,150 --> 00:06:17,190 A giant is any ethernet frame 164 00:06:17,190 --> 00:06:22,190 that exceeds the 802.3 frame size of 1,518 bytes. 165 00:06:22,230 --> 00:06:24,660 It's really large, so it's a giant. 166 00:06:24,660 --> 00:06:26,520 Throttles are going to occur when the interface 167 00:06:26,520 --> 00:06:28,740 fails to buffer the incoming packets. 168 00:06:28,740 --> 00:06:31,020 If this is a high number, this is an indicator 169 00:06:31,020 --> 00:06:33,150 that you may be having quality of service issues 170 00:06:33,150 --> 00:06:34,770 to your end users. 171 00:06:34,770 --> 00:06:39,360 Next, we have input errors, CRC, frame overrun and ignored. 172 00:06:39,360 --> 00:06:41,070 The input error counter will go up 173 00:06:41,070 --> 00:06:42,990 whenever the interface is receiving a frame 174 00:06:42,990 --> 00:06:44,490 with any kind of error in it. 175 00:06:44,490 --> 00:06:46,980 This can be something like a runt, a giant, 176 00:06:46,980 --> 00:06:50,910 no buffer available, CRC errors or other things like that. 177 00:06:50,910 --> 00:06:53,310 CRC is the number of packets that were received 178 00:06:53,310 --> 00:06:55,560 but failed the cyclic redundancy checksum 179 00:06:55,560 --> 00:06:58,260 or CRC check upon receiving them. 180 00:06:58,260 --> 00:06:59,370 If the checksum generated 181 00:06:59,370 --> 00:07:01,200 by the sender doesn't match the one calculated 182 00:07:01,200 --> 00:07:03,480 by this interface, when it receives that frame, 183 00:07:03,480 --> 00:07:06,720 a CRC error is counted and the packet gets rejected. 184 00:07:06,720 --> 00:07:09,000 Now, frame is used to count the number of packets 185 00:07:09,000 --> 00:07:10,260 where a CRC error 186 00:07:10,260 --> 00:07:13,560 and a non integer number of octets was received. 187 00:07:13,560 --> 00:07:15,870 Overrun is used to count how often the interface 188 00:07:15,870 --> 00:07:17,550 was unable to receive traffic 189 00:07:17,550 --> 00:07:19,860 due to an insufficient hardware buffer. 190 00:07:19,860 --> 00:07:22,410 Ignored is going to be used to count the number of packets 191 00:07:22,410 --> 00:07:24,840 that the interface ignored since the hardware interface 192 00:07:24,840 --> 00:07:26,760 was low on the internal buffers. 193 00:07:26,760 --> 00:07:28,890 If you're experiencing a lot of noise on the connection 194 00:07:28,890 --> 00:07:31,320 or broadcast storm, this ignored count 195 00:07:31,320 --> 00:07:33,600 will start to rise drastically. 196 00:07:33,600 --> 00:07:36,360 Next, we have the watchdog counter, which is used to count 197 00:07:36,360 --> 00:07:39,300 how many times the watchdog timer has expired. 198 00:07:39,300 --> 00:07:43,560 This happens whenever a packet over 2048 bytes is received. 199 00:07:43,560 --> 00:07:45,390 The next line contains the input packets 200 00:07:45,390 --> 00:07:47,070 with dribble condition detected, 201 00:07:47,070 --> 00:07:49,320 which means that a slightly longer than default frame 202 00:07:49,320 --> 00:07:50,880 was received by the interface. 203 00:07:50,880 --> 00:07:52,710 For example, we talked about the fact 204 00:07:52,710 --> 00:07:55,800 that the MTU size was 1500 bytes by default, 205 00:07:55,800 --> 00:07:57,900 but a frame wasn't considered a giant 206 00:07:57,900 --> 00:08:00,900 until it reached 1,518 bytes. 207 00:08:00,900 --> 00:08:04,560 So if I got a frame that was 1,510 bytes inside, 208 00:08:04,560 --> 00:08:06,810 it's technically above the MTU size, 209 00:08:06,810 --> 00:08:10,470 but it's not yet a giant, so it would still be processed, 210 00:08:10,470 --> 00:08:13,380 but it would be added here on the dribble condition counter 211 00:08:13,380 --> 00:08:15,060 so I can know that I'm starting to get packets 212 00:08:15,060 --> 00:08:17,160 above 1500 bytes. 213 00:08:17,160 --> 00:08:19,470 Next, we have the packet output counter, 214 00:08:19,470 --> 00:08:21,480 and this is the number of packets that have been sent 215 00:08:21,480 --> 00:08:24,090 and the size of those transmissions in bytes. 216 00:08:24,090 --> 00:08:25,710 The under run is the number of times 217 00:08:25,710 --> 00:08:28,740 the sender has operated faster than the router can handle, 218 00:08:28,740 --> 00:08:31,800 and this causes buffers or drop packets. 219 00:08:31,800 --> 00:08:33,690 Next, we have the output errors, 220 00:08:33,690 --> 00:08:35,429 and this is just like our input errors. 221 00:08:35,429 --> 00:08:37,320 The only difference is we're now counting the number 222 00:08:37,320 --> 00:08:39,299 of collisions and the interface resets 223 00:08:39,299 --> 00:08:40,980 that are occurring as a result. 224 00:08:40,980 --> 00:08:42,840 A collision is counted anytime a packet 225 00:08:42,840 --> 00:08:46,230 needs to be remitted because an ethernet collision occurred. 226 00:08:46,230 --> 00:08:49,980 Since we're using full duplex, this number should be zero. 227 00:08:49,980 --> 00:08:52,470 If it's not zero, something's wrong. 228 00:08:52,470 --> 00:08:54,720 Next, we have the interface reset, 229 00:08:54,720 --> 00:08:56,760 and this the number of times an interface 230 00:08:56,760 --> 00:09:00,210 had to be completely reset since the last reboot. 231 00:09:00,210 --> 00:09:02,820 Next, we have unknown protocol drops. 232 00:09:02,820 --> 00:09:04,320 Anytime a protocol drops, 233 00:09:04,320 --> 00:09:06,750 but our device can't determine what protocol it was, 234 00:09:06,750 --> 00:09:09,690 it's going to be listed under the unknown protocol drops. 235 00:09:09,690 --> 00:09:12,570 For example, if you're not supposed to receive older types 236 00:09:12,570 --> 00:09:16,020 of protocols like IPX traffic and Apple Talk on your router, 237 00:09:16,020 --> 00:09:18,870 but somebody sends you a message that's formatted that way, 238 00:09:18,870 --> 00:09:20,190 your router's going to drop it 239 00:09:20,190 --> 00:09:22,050 and it's not going to know what it was 240 00:09:22,050 --> 00:09:24,570 because it's not a properly formatted IP message 241 00:09:24,570 --> 00:09:28,260 or an ethernet frame, so that counter is going to go up. 242 00:09:28,260 --> 00:09:31,560 Next, we have babbles, late collision and deferred. 243 00:09:31,560 --> 00:09:33,273 Now, a babble is used to count any frame 244 00:09:33,273 --> 00:09:37,710 that is transmitted that is larger than 1,518 bytes. 245 00:09:37,710 --> 00:09:39,330 This is similar to our giants, 246 00:09:39,330 --> 00:09:41,790 but we're going to use this when we're transmitting 247 00:09:41,790 --> 00:09:44,760 instead of receiving, a babble is for transmission, 248 00:09:44,760 --> 00:09:46,770 a giant is for receipt. 249 00:09:46,770 --> 00:09:48,780 Late collisions are going to be used to count the number 250 00:09:48,780 --> 00:09:50,880 of collisions that occur after the interface 251 00:09:50,880 --> 00:09:52,740 started transmitting its frame 252 00:09:52,740 --> 00:09:54,840 and deferred is used to count the number of frames 253 00:09:54,840 --> 00:09:56,370 that were transmitted successfully 254 00:09:56,370 --> 00:09:58,920 after waiting because the media was busy. 255 00:09:58,920 --> 00:10:02,130 So if your devices are using CSMA/CD 256 00:10:02,130 --> 00:10:05,310 or collision detection, it's going to detect the media is busy. 257 00:10:05,310 --> 00:10:07,680 It's going to wait, and then it's going to transmit. 258 00:10:07,680 --> 00:10:09,600 When this happens, this number's going to go up 259 00:10:09,600 --> 00:10:11,100 because it had to wait. 260 00:10:11,100 --> 00:10:13,500 Again, we should see zero for late collisions 261 00:10:13,500 --> 00:10:14,400 and deferred here 262 00:10:14,400 --> 00:10:16,710 because we're using a full duplex connection, 263 00:10:16,710 --> 00:10:18,570 but if we're using a half duplex connection, 264 00:10:18,570 --> 00:10:20,460 there will be some numbers there. 265 00:10:20,460 --> 00:10:23,520 Next, we have the lost carrier and the no carrier. 266 00:10:23,520 --> 00:10:25,980 This is the number of times that the carrier was lost 267 00:10:25,980 --> 00:10:28,110 or not present during the transmission. 268 00:10:28,110 --> 00:10:29,370 The carrier we're talking about here 269 00:10:29,370 --> 00:10:31,530 is the signal on the connection. 270 00:10:31,530 --> 00:10:33,810 Finally, we have the output buffer failures 271 00:10:33,810 --> 00:10:36,150 and swapped out, the output buffer failure 272 00:10:36,150 --> 00:10:37,620 is going to be used to count the number 273 00:10:37,620 --> 00:10:41,130 of times a packet was not output from the output hold queue 274 00:10:41,130 --> 00:10:43,350 because of a shortage of shared memory. 275 00:10:43,350 --> 00:10:45,930 An output buffer swap out is going to be the number 276 00:10:45,930 --> 00:10:47,880 of packets stored in the main memory 277 00:10:47,880 --> 00:10:49,500 when the queue was full. 278 00:10:49,500 --> 00:10:51,240 If this number is very high, 279 00:10:51,240 --> 00:10:52,860 that means that you're likely experiencing 280 00:10:52,860 --> 00:10:54,570 a busy time in your networks. 281 00:10:54,570 --> 00:10:56,610 Now, for the exam, you don't need to know 282 00:10:56,610 --> 00:10:59,130 all of these things and memorize all their definitions, 283 00:10:59,130 --> 00:11:01,350 but you should be aware of some key statistics 284 00:11:01,350 --> 00:11:02,880 here on the interface. 285 00:11:02,880 --> 00:11:04,380 Things like the link state, 286 00:11:04,380 --> 00:11:06,060 the speed and duplex status, 287 00:11:06,060 --> 00:11:08,160 the send and receive traffic statistics, 288 00:11:08,160 --> 00:11:11,520 the cyclic redundancy check statistics, the protocol packet 289 00:11:11,520 --> 00:11:14,850 and byte counts, the CRC errors, the giants, 290 00:11:14,850 --> 00:11:17,340 the runts and the encapsulation errors. 291 00:11:17,340 --> 00:11:19,200 On the exam, you may get a question 292 00:11:19,200 --> 00:11:20,880 that involves troubleshooting a device 293 00:11:20,880 --> 00:11:22,740 and you're going to see an interface statistic screen 294 00:11:22,740 --> 00:11:24,660 like this, and then you're going to have 295 00:11:24,660 --> 00:11:26,670 to recommend a solution to that problem. 296 00:11:26,670 --> 00:11:29,010 For example, if the question asks why the device 297 00:11:29,010 --> 00:11:31,020 is operating slowly and you see the connection 298 00:11:31,020 --> 00:11:33,420 set to half duplex instead of full duplex, 299 00:11:33,420 --> 00:11:35,130 that would be a reason for the slowdown 300 00:11:35,130 --> 00:11:37,560 because you effectively cut your bandwidth in half 301 00:11:37,560 --> 00:11:39,870 because it's to listen before transmitting. 302 00:11:39,870 --> 00:11:42,030 Or if you see a large amount of collisions, 303 00:11:42,030 --> 00:11:43,530 but you're running full duplex, 304 00:11:43,530 --> 00:11:45,480 that would indicate there's two devices connected 305 00:11:45,480 --> 00:11:48,720 to the same switchboard and that is causing you issues. 306 00:11:48,720 --> 00:11:51,540 Or maybe you see there's a lot of CRC errors. 307 00:11:51,540 --> 00:11:53,670 This could indicate a dirty fiber connector 308 00:11:53,670 --> 00:11:55,470 or an unshielded twisted cable 309 00:11:55,470 --> 00:11:58,380 that's subject to too much electromagnetic interference. 310 00:11:58,380 --> 00:12:00,600 This could be caused by lots of different things 311 00:12:00,600 --> 00:12:02,280 such as your cable being improperly run 312 00:12:02,280 --> 00:12:03,360 over a fluorescent light 313 00:12:03,360 --> 00:12:05,640 or near a power line or something like that. 314 00:12:05,640 --> 00:12:07,260 My point is, it's important to be able 315 00:12:07,260 --> 00:12:08,940 to read the interface statistics 316 00:12:08,940 --> 00:12:09,960 so you can then troubleshoot 317 00:12:09,960 --> 00:12:11,340 your network connectivity issues 318 00:12:11,340 --> 00:12:12,790 in your routers and switches.