1 00:00:00,000 --> 00:00:00,956 2 00:00:00,956 --> 00:00:04,302 [AUDIO LOGO] 3 00:00:04,302 --> 00:00:07,170 4 00:00:07,170 --> 00:00:12,360 So in this video, let's jump in and take a deeper look at IS-IS 5 00:00:12,360 --> 00:00:15,240 adjacencies or neighborships. 6 00:00:15,240 --> 00:00:18,330 Now there's really sort of two major attributes 7 00:00:18,330 --> 00:00:19,810 here we need to look at. 8 00:00:19,810 --> 00:00:22,380 The first is the network type. 9 00:00:22,380 --> 00:00:24,630 And this is very similar to the network types 10 00:00:24,630 --> 00:00:27,220 that we have in OSPF as well. 11 00:00:27,220 --> 00:00:31,330 But IS-IS has two network types that we need to look at, 12 00:00:31,330 --> 00:00:33,460 so we'll look at both of those. 13 00:00:33,460 --> 00:00:36,180 The other thing that affects adjacency 14 00:00:36,180 --> 00:00:38,410 is the adjacency level. 15 00:00:38,410 --> 00:00:43,890 Remember, we have Level 1 and Level 2 in IS-IS, 16 00:00:43,890 --> 00:00:48,210 and we form different adjacencies for each level. 17 00:00:48,210 --> 00:00:51,270 Now depending exactly what level each router is in 18 00:00:51,270 --> 00:00:55,710 and how we configure our interfaces will determine which 19 00:00:55,710 --> 00:00:59,920 level or levels of adjacency that will form. 20 00:00:59,920 --> 00:01:03,060 So let's go ahead and jump in and look at those details. 21 00:01:03,060 --> 00:01:08,000 We'll start off by looking at the different network types. 22 00:01:08,000 --> 00:01:10,750 So as we mentioned during our introduction, 23 00:01:10,750 --> 00:01:15,640 IS-IS does, in fact, support two different network types 24 00:01:15,640 --> 00:01:18,100 for our different media types. 25 00:01:18,100 --> 00:01:21,130 It really depends on what type of neighborships 26 00:01:21,130 --> 00:01:22,600 we want to form. 27 00:01:22,600 --> 00:01:25,940 These two types are first broadcast. 28 00:01:25,940 --> 00:01:27,640 And this is going to be generally used 29 00:01:27,640 --> 00:01:30,080 for multi-access networks. 30 00:01:30,080 --> 00:01:32,770 This is when there's going to be more than one device 31 00:01:32,770 --> 00:01:36,910 on the same segment or broadcast domain. 32 00:01:36,910 --> 00:01:39,980 The other choice is point-to-point. 33 00:01:39,980 --> 00:01:43,010 And as the name pretty much implies, 34 00:01:43,010 --> 00:01:46,810 this is going to be for almost all other topologies, where 35 00:01:46,810 --> 00:01:49,540 we're just going to have two routers, 1 36 00:01:49,540 --> 00:01:51,790 on each end of a circuit. 37 00:01:51,790 --> 00:01:55,610 Each of these network types have different attributes. 38 00:01:55,610 --> 00:01:58,340 The broadcast network type, as we mentioned, 39 00:01:58,340 --> 00:02:01,900 is really for multi-access networks. 40 00:02:01,900 --> 00:02:06,070 Of course, the biggest example of this would be Ethernet. 41 00:02:06,070 --> 00:02:09,770 But also, full-mesh WANs. 42 00:02:09,770 --> 00:02:13,720 Remember that although we don't use it very often anymore, 43 00:02:13,720 --> 00:02:16,780 things like Frame Relay was originally 44 00:02:16,780 --> 00:02:19,180 designed to be a full mesh. 45 00:02:19,180 --> 00:02:22,600 And therefore, the broadcast network type 46 00:02:22,600 --> 00:02:25,490 could be appropriate in that environment. 47 00:02:25,490 --> 00:02:28,720 On the other hand, if the Frame Relay was not 48 00:02:28,720 --> 00:02:31,930 running as a full mesh, then point-to-point 49 00:02:31,930 --> 00:02:33,760 would probably be a better choice 50 00:02:33,760 --> 00:02:36,380 in that type of an environment. 51 00:02:36,380 --> 00:02:39,070 Now broadcast network type uses something 52 00:02:39,070 --> 00:02:46,741 called a Designated Intermediate System, or a D-I-S or a DIS. 53 00:02:46,741 --> 00:02:54,710 This is very similar to the OSPF, DR, or designated router. 54 00:02:54,710 --> 00:02:57,310 Now, one sort of fundamental difference 55 00:02:57,310 --> 00:03:01,060 about the DIS-- and we will talk about this in more detail 56 00:03:01,060 --> 00:03:02,120 later. 57 00:03:02,120 --> 00:03:04,090 But one fundamental difference here 58 00:03:04,090 --> 00:03:07,960 is where OSPF has something called 59 00:03:07,960 --> 00:03:13,000 the BDR, which, of course, is to back up the DR should it fail. 60 00:03:13,000 --> 00:03:18,250 IS-IS does not have any similar concept. 61 00:03:18,250 --> 00:03:22,720 If the DIS fails, then another one is simply elected. 62 00:03:22,720 --> 00:03:24,850 Also, similar to other routing protocols, 63 00:03:24,850 --> 00:03:28,750 this does use multicast for its communication. 64 00:03:28,750 --> 00:03:34,970 The hello timer actually defaults to 3.3 seconds. 65 00:03:34,970 --> 00:03:38,920 Again, the idea here being that a multi-access network 66 00:03:38,920 --> 00:03:42,970 is generally considered faster than what 67 00:03:42,970 --> 00:03:45,190 a point-to-point system would be. 68 00:03:45,190 --> 00:03:47,720 Also, keep in mind that part of the point of this 69 00:03:47,720 --> 00:03:53,050 is this does create a full mesh of adjacencies. 70 00:03:53,050 --> 00:03:56,290 That's sort of why it had to be a full-mesh WAN for this 71 00:03:56,290 --> 00:04:00,880 to make any sense so that we can form all those neighborships. 72 00:04:00,880 --> 00:04:02,560 And the same thing with Ethernet. 73 00:04:02,560 --> 00:04:05,380 Again, the assumption is that all the devices 74 00:04:05,380 --> 00:04:08,380 can talk to all of the devices on that segment. 75 00:04:08,380 --> 00:04:12,010 Therefore, we create a full mesh of adjacencies. 76 00:04:12,010 --> 00:04:15,070 Now, this, of course, does create the potential 77 00:04:15,070 --> 00:04:17,170 for a large number of adjacencies. 78 00:04:17,170 --> 00:04:18,790 We have the formula here. 79 00:04:18,790 --> 00:04:23,950 It's just going to be n times n minus 1 divided by 2 because we 80 00:04:23,950 --> 00:04:27,280 don't create two neighborships between each router. 81 00:04:27,280 --> 00:04:31,040 But this can still create a large number of adjacencies, 82 00:04:31,040 --> 00:04:34,600 so just keep this in mind if we have a lot of routers 83 00:04:34,600 --> 00:04:36,130 on a single segment. 84 00:04:36,130 --> 00:04:38,680 It's generally not a problem but always something 85 00:04:38,680 --> 00:04:40,300 good to keep in mind. 86 00:04:40,300 --> 00:04:45,070 Broadcast networks also use either Level 1 or Level 2 IS-IS 87 00:04:45,070 --> 00:04:46,210 hellos. 88 00:04:46,210 --> 00:04:49,510 And these are referred to as LAN hellos, 89 00:04:49,510 --> 00:04:52,850 and we will see this in just a little bit. 90 00:04:52,850 --> 00:04:55,000 Now, of course, the point-to-point networks 91 00:04:55,000 --> 00:04:57,340 have slightly different attributes. 92 00:04:57,340 --> 00:04:59,570 First, these are meant, of course, 93 00:04:59,570 --> 00:05:03,340 for use on point-to-point networks, just some examples 94 00:05:03,340 --> 00:05:06,670 being PPP, which, of course, is point-to-point. 95 00:05:06,670 --> 00:05:10,000 That's obviously going to be a point-to-point network type. 96 00:05:10,000 --> 00:05:14,350 HDLC; partial-mesh WANs, like Frame Relay, 97 00:05:14,350 --> 00:05:16,010 like we mentioned earlier. 98 00:05:16,010 --> 00:05:18,250 Now this, of course, is not going 99 00:05:18,250 --> 00:05:22,390 to use a DIS because it's only two routers. 100 00:05:22,390 --> 00:05:28,270 Remember that the point of the DIS much like the DR in OSPF 101 00:05:28,270 --> 00:05:33,400 is to reduce the flooding of our link state database updates 102 00:05:33,400 --> 00:05:35,480 on that LAN segment. 103 00:05:35,480 --> 00:05:37,570 Now, if there's only two neighbors 104 00:05:37,570 --> 00:05:39,700 like in a point-to-point connection, 105 00:05:39,700 --> 00:05:41,770 I have to send you my updates, and you 106 00:05:41,770 --> 00:05:43,480 have to send me your updates. 107 00:05:43,480 --> 00:05:45,740 There's really no way to reduce that. 108 00:05:45,740 --> 00:05:50,420 So there's no point in a DR in OSPF or, of course, 109 00:05:50,420 --> 00:05:54,820 a DIS in IS-IS on a point-to-point link. 110 00:05:54,820 --> 00:05:57,430 It just wouldn't make any sense. 111 00:05:57,430 --> 00:05:59,860 Also, since there's only the two devices, 112 00:05:59,860 --> 00:06:03,550 we can simply do our communication with unicast. 113 00:06:03,550 --> 00:06:07,550 The hello timer is actually going to be slower here. 114 00:06:07,550 --> 00:06:10,710 Notice the hello timer is 10 seconds. 115 00:06:10,710 --> 00:06:12,790 Now these, of course, can be adjusted. 116 00:06:12,790 --> 00:06:15,370 However, it defaults to 10 seconds 117 00:06:15,370 --> 00:06:23,440 because traditionally, things like PPP, HDLC, WAN links, 118 00:06:23,440 --> 00:06:26,530 these were generally considered to be slower. 119 00:06:26,530 --> 00:06:28,120 Since these are generally considered 120 00:06:28,120 --> 00:06:32,290 to be slower than the LAN, we slowed down the timers. 121 00:06:32,290 --> 00:06:34,210 Now, of course, in today's environment, 122 00:06:34,210 --> 00:06:36,460 that may not always be the case. 123 00:06:36,460 --> 00:06:40,370 Therefore, we can, of course speed this up. 124 00:06:40,370 --> 00:06:43,120 Also note that these do use their own special type 125 00:06:43,120 --> 00:06:44,080 of hello. 126 00:06:44,080 --> 00:06:48,040 They're still called IIHs because they're IS-IS hellos, 127 00:06:48,040 --> 00:06:53,410 but it is a point-to-point hello rather than a LAN hello. 128 00:06:53,410 --> 00:06:57,800 And we'll see this difference as we move into our demonstration. 129 00:06:57,800 --> 00:07:00,460 The other thing we mentioned during our introduction 130 00:07:00,460 --> 00:07:04,450 was that we're going to form different adjacencies based 131 00:07:04,450 --> 00:07:08,380 on the area ID and the router type. 132 00:07:08,380 --> 00:07:11,110 And again, what we mean here is whether it's a Level 133 00:07:11,110 --> 00:07:15,940 1 or a Level 2 or both device. 134 00:07:15,940 --> 00:07:19,210 And even more specifically, the link type. 135 00:07:19,210 --> 00:07:22,070 So let's take a look at the different combinations 136 00:07:22,070 --> 00:07:25,720 and what will or will not form a neighborship. 137 00:07:25,720 --> 00:07:30,010 So our first example here, we have two routers. 138 00:07:30,010 --> 00:07:31,900 They're in the same area. 139 00:07:31,900 --> 00:07:34,150 That's denoted by the single box. 140 00:07:34,150 --> 00:07:36,490 And they're both Level 1. 141 00:07:36,490 --> 00:07:40,390 So the first question is, will this form an adjacency? 142 00:07:40,390 --> 00:07:43,450 And the answer to that is yes, it will. 143 00:07:43,450 --> 00:07:48,250 And, in fact, what it will form is a Level 1 adjacency. 144 00:07:48,250 --> 00:07:53,260 What about Level 1, Level 2 in the same area? 145 00:07:53,260 --> 00:07:56,500 The answer to this one is no, it will not. 146 00:07:56,500 --> 00:08:00,790 There has to be a level in common in order for these 147 00:08:00,790 --> 00:08:02,350 to form a neighborship. 148 00:08:02,350 --> 00:08:05,200 So we can have one Level 1 and one Level 2 149 00:08:05,200 --> 00:08:07,000 form a neighborship. 150 00:08:07,000 --> 00:08:12,010 How about a Level 1 and a Level 1-Level 2 router? 151 00:08:12,010 --> 00:08:14,560 The answer here is once again yes, 152 00:08:14,560 --> 00:08:16,198 they will form a neighborship. 153 00:08:16,198 --> 00:08:18,490 And, of course, they're going to form that neighborship 154 00:08:18,490 --> 00:08:20,960 over the only level they have in common. 155 00:08:20,960 --> 00:08:24,580 So this again will be a Level 1 adjacency. 156 00:08:24,580 --> 00:08:30,440 What about an L2 and an L1 L2 in the same area? 157 00:08:30,440 --> 00:08:34,990 Now, in the same area, again, we can do just Level 1 158 00:08:34,990 --> 00:08:37,179 like we did in our first example. 159 00:08:37,179 --> 00:08:40,580 But guess what, Level 2 will work as well. 160 00:08:40,580 --> 00:08:43,750 So first, yes, this will form an adjacency. 161 00:08:43,750 --> 00:08:45,640 And, of course, what it's going to do 162 00:08:45,640 --> 00:08:49,420 is it's going to form a Level 2 adjacency. 163 00:08:49,420 --> 00:08:55,870 Our next choice is a Level 1 and a Level 2 for both devices. 164 00:08:55,870 --> 00:08:59,020 The answer to this one is first off, yes, 165 00:08:59,020 --> 00:09:01,480 they will definitely form an adjacency. 166 00:09:01,480 --> 00:09:03,640 But what they'll do is they'll actually 167 00:09:03,640 --> 00:09:08,140 form two separate adjacencies, one for Level 1 and one 168 00:09:08,140 --> 00:09:09,490 for Level 2. 169 00:09:09,490 --> 00:09:11,710 So in this case, you're going to end up 170 00:09:11,710 --> 00:09:14,960 with two adjacencies between the routers. 171 00:09:14,960 --> 00:09:18,130 So now let's talk about what happens if the routers are 172 00:09:18,130 --> 00:09:19,550 in different areas. 173 00:09:19,550 --> 00:09:24,620 So here we have two Level 1 routers in two different areas. 174 00:09:24,620 --> 00:09:29,290 Now, in order to join areas, this has to be Level 2. 175 00:09:29,290 --> 00:09:33,220 So our simple answer here is this simply will not work. 176 00:09:33,220 --> 00:09:39,250 We will get no adjacency Level 1 to Level 1 between areas. 177 00:09:39,250 --> 00:09:40,750 What about Level 2? 178 00:09:40,750 --> 00:09:43,930 Well, as we just stated, this is sort of exactly the purpose 179 00:09:43,930 --> 00:09:45,010 of Level 2. 180 00:09:45,010 --> 00:09:48,310 So this is definitely going to form an adjacency. 181 00:09:48,310 --> 00:09:51,490 And since they're both Level 2 and Level 2 182 00:09:51,490 --> 00:09:53,830 is the only adjacency that will work here, 183 00:09:53,830 --> 00:09:57,550 the adjacency will, of course, be Level 2. 184 00:09:57,550 --> 00:10:01,900 Next option, Level 2 to Level 1-Level 2. 185 00:10:01,900 --> 00:10:04,840 Well, once again, this is a good combination 186 00:10:04,840 --> 00:10:07,240 because we have both devices that 187 00:10:07,240 --> 00:10:12,410 are Level 2, which means they will form a Level 2 adjacency. 188 00:10:12,410 --> 00:10:14,530 So this again will work fine. 189 00:10:14,530 --> 00:10:16,580 This one is a little bit different. 190 00:10:16,580 --> 00:10:20,980 What about an L1-L2 to an L1-L2? 191 00:10:20,980 --> 00:10:24,460 Well, again, they will form a neighbor relationship 192 00:10:24,460 --> 00:10:28,240 or an adjacency because we have that Level 2. 193 00:10:28,240 --> 00:10:32,770 But keep in mind that only the Level 2 will work here. 194 00:10:32,770 --> 00:10:35,380 We will not get a Level 1 adjacency 195 00:10:35,380 --> 00:10:38,330 because they're between areas. 196 00:10:38,330 --> 00:10:40,750 So now let's do a quick demonstration 197 00:10:40,750 --> 00:10:44,290 of the different network types and a little bit 198 00:10:44,290 --> 00:10:48,070 about the adjacencies by taking a look at the command line, 199 00:10:48,070 --> 00:10:51,160 and we'll jump in and take a look at the hello packets 200 00:10:51,160 --> 00:10:52,510 in Wireshark. 201 00:10:52,510 --> 00:10:54,490 Let's begin by taking a look at the topology. 202 00:10:54,490 --> 00:10:56,540 Just so we have a rough idea of what's going on. 203 00:10:56,540 --> 00:10:58,660 And then we'll jump into the CLI. 204 00:10:58,660 --> 00:11:00,460 So for this demonstration, we'll just 205 00:11:00,460 --> 00:11:03,730 be using the IS-IS basic topology. 206 00:11:03,730 --> 00:11:05,350 We're going to be mostly focusing 207 00:11:05,350 --> 00:11:10,160 on router 1 and the link between R1 and R2, 208 00:11:10,160 --> 00:11:13,850 which as we can see here is in fact Ethernet. 209 00:11:13,850 --> 00:11:18,560 It's out both of these routers gigabit 0000 interface. 210 00:11:18,560 --> 00:11:23,390 It is currently set to a LAN network type, which we'll see. 211 00:11:23,390 --> 00:11:27,150 And then we'll convert this to point-to-point. 212 00:11:27,150 --> 00:11:29,600 So let's get started by just jumping into the command 213 00:11:29,600 --> 00:11:32,200 line on router 1. 214 00:11:32,200 --> 00:11:36,100 So first, let's go ahead and look at that gigabit 0000 215 00:11:36,100 --> 00:11:37,280 interface. 216 00:11:37,280 --> 00:11:42,160 So let's just show IS-IS interface gig 0000. 217 00:11:42,160 --> 00:11:45,320 What we're looking for specifically is right here. 218 00:11:45,320 --> 00:11:49,420 It's currently set to media type, LAN. 219 00:11:49,420 --> 00:11:51,350 This is what we're going to be changing. 220 00:11:51,350 --> 00:11:53,560 However, before we do, we're going 221 00:11:53,560 --> 00:11:55,540 to hop over into Wireshark and take 222 00:11:55,540 --> 00:11:59,110 a look at these hellos that are being sent between router 1 223 00:11:59,110 --> 00:12:00,520 and router 2. 224 00:12:00,520 --> 00:12:04,600 Also, note that this is also a Level 1 circuit. 225 00:12:04,600 --> 00:12:07,310 We'll see that in Wireshark as well. 226 00:12:07,310 --> 00:12:12,430 So here we have a capture of router 1's gigabit 0000 227 00:12:12,430 --> 00:12:17,770 interface, and the capture has been filtered for IS-IS. 228 00:12:17,770 --> 00:12:20,590 Now, if we look here, the very first packet 229 00:12:20,590 --> 00:12:23,080 is actually an IS-IS hello. 230 00:12:23,080 --> 00:12:24,970 We can actually see in the info that it's 231 00:12:24,970 --> 00:12:32,230 an L1 hello specifically from system ID 1, which is router 1. 232 00:12:32,230 --> 00:12:35,740 If we open the ISO header, we can see right here 233 00:12:35,740 --> 00:12:38,500 that this is a Level 1 hello. 234 00:12:38,500 --> 00:12:40,540 It's type 15. 235 00:12:40,540 --> 00:12:43,660 We can see the same thing if we look at a hello coming 236 00:12:43,660 --> 00:12:45,310 from router 2. 237 00:12:45,310 --> 00:12:47,920 In this example, packet 5 happens 238 00:12:47,920 --> 00:12:50,920 to be a hello coming from router 2, 239 00:12:50,920 --> 00:12:56,960 and we see that just like router 1, this is an L1 hello type 15. 240 00:12:56,960 --> 00:13:01,330 So now let's go ahead and change that gigabit 0000 link over 241 00:13:01,330 --> 00:13:02,870 to point-to-point. 242 00:13:02,870 --> 00:13:05,530 So simply go into configuration mode 243 00:13:05,530 --> 00:13:07,780 then into the router IS-IS process, 244 00:13:07,780 --> 00:13:11,740 ours is called SP1 then into our interface. 245 00:13:11,740 --> 00:13:15,530 And all we have to say here is point-to-point. 246 00:13:15,530 --> 00:13:18,340 Now pretty much as soon as we commit this, 247 00:13:18,340 --> 00:13:20,740 we're going to start getting console messages 248 00:13:20,740 --> 00:13:25,960 where we were receiving a type 15 Hello when 249 00:13:25,960 --> 00:13:29,470 what we're expecting is a point-to-point hello. 250 00:13:29,470 --> 00:13:31,390 So it's telling us that we're receiving 251 00:13:31,390 --> 00:13:33,470 the incorrect hello type. 252 00:13:33,470 --> 00:13:36,320 Now we have to change this on router 2 as well. 253 00:13:36,320 --> 00:13:39,340 We see we have the message on router 2 also. 254 00:13:39,340 --> 00:13:42,160 Once again, all we have to do is go into our interface, 255 00:13:42,160 --> 00:13:44,180 change it to point-to-point. 256 00:13:44,180 --> 00:13:45,280 So we'll verify this. 257 00:13:45,280 --> 00:13:48,640 Let's go back over to router 1 just to do the verification. 258 00:13:48,640 --> 00:13:51,440 Let's start with a show IS-IS neighbor. 259 00:13:51,440 --> 00:13:53,740 We see that the connection to router 2 260 00:13:53,740 --> 00:13:56,630 is in fact now set to point-to-point. 261 00:13:56,630 --> 00:14:01,330 We can also verify this with the show IS-IS interface again 262 00:14:01,330 --> 00:14:03,580 for gig 0000. 263 00:14:03,580 --> 00:14:09,190 And we see that now the media type is set to point-to-point. 264 00:14:09,190 --> 00:14:11,670 Let's go look at this on Wireshark. 265 00:14:11,670 --> 00:14:14,250 So once again, we've captured the hellos. 266 00:14:14,250 --> 00:14:17,160 Notice, however, under info, it now 267 00:14:17,160 --> 00:14:20,340 specifically says point-to-point hello. 268 00:14:20,340 --> 00:14:23,730 And if we look down here at our headers, 269 00:14:23,730 --> 00:14:26,460 specifically, if we open up the ISO, 270 00:14:26,460 --> 00:14:32,190 we now see that this is a point-to-point hello type 17. 271 00:14:32,190 --> 00:14:35,550 So we can see that it's using a completely different hello type 272 00:14:35,550 --> 00:14:38,610 on the point-to-point connection. 273 00:14:38,610 --> 00:14:42,960 So in this video, we saw a little bit more information 274 00:14:42,960 --> 00:14:47,790 about the adjacencies that have to be formed with IS-IS. 275 00:14:47,790 --> 00:14:50,550 We started off by taking a look at the different network 276 00:14:50,550 --> 00:14:53,710 types, broadcast versus point-to-point. 277 00:14:53,710 --> 00:14:57,150 And then we also talked a bit about the neighborships that'll 278 00:14:57,150 --> 00:15:01,920 be formed between Level 1 and Level 2 devices, depending 279 00:15:01,920 --> 00:15:04,890 if they're in the same area, different areas, and all 280 00:15:04,890 --> 00:15:06,510 the different combinations. 281 00:15:06,510 --> 00:15:08,700 I hope this has been informative for you, 282 00:15:08,700 --> 00:15:11,810 and I'd like to thank you for viewing. 283 00:15:11,810 --> 00:15:15,000