1 00:00:08,440 --> 00:00:11,620 Alright, so up to this point, if you've been watching the videos from 2 00:00:11,620 --> 00:00:15,920 the beginning up till now, I've sort of broken it up into sections in 3 00:00:15,920 --> 00:00:19,320 order to highlight each section, really give the details of what's happening 4 00:00:19,320 --> 00:00:24,100 in each process or as each trigger happens in the PIM process. 5 00:00:24,100 --> 00:00:29,960 We had a section on, you know, the shared tree being built and the triggers 6 00:00:29,960 --> 00:00:33,640 and the messages that happen with that, then we had another video about 7 00:00:33,640 --> 00:00:38,180 the registration process as the source starts up what that looks like. 8 00:00:38,180 --> 00:00:42,240 Then we had another section on joining the shortest path tree. 9 00:00:42,240 --> 00:00:44,300 So, I'm going to bring it all into focus. 10 00:00:44,300 --> 00:00:47,360 Now, I'm just going to do a quick review on the whiteboard of all that 11 00:00:47,360 --> 00:00:49,060 stuff as it happens. 12 00:00:49,060 --> 00:00:51,140 Not going to do any more sniffer traces or labs. 13 00:00:51,140 --> 00:00:54,480 We've already done that in the previous trait in the previous sections. 14 00:00:54,480 --> 00:00:58,600 I'll just show you on the whiteboard end to end the whole process as it 15 00:00:58,600 --> 00:01:01,540 happens. So, hopefully that will bring it into focus if you were sort 16 00:01:01,540 --> 00:01:05,640 of stuck right now seeing the forest through the trees as the saying goes. 17 00:01:05,640 --> 00:01:09,440 So, let's go back to our whiteboard here. 18 00:01:09,440 --> 00:01:19,960 Okay, so now with multicast, one of two things could happen first. 19 00:01:19,960 --> 00:01:24,840 Either the receivers could start joining the multicast before the multicast 20 00:01:24,840 --> 00:01:27,640 has even started, and that could certainly happen. 21 00:01:27,640 --> 00:01:30,580 You know, for example, if you find out that your CEO is going to be having 22 00:01:30,580 --> 00:01:35,560 a video at three o'clock today of some big new bonus structure in your 23 00:01:35,560 --> 00:01:39,560 company. Well, before that even video starts going out at three o'clock, 24 00:01:39,560 --> 00:01:42,820 people in their cubes will probably start joining it, you know, five or 25 00:01:42,820 --> 00:01:44,840 ten minutes before the video even starts. 26 00:01:44,840 --> 00:01:50,240 So, that could happen where, you know, maybe you've got a video stream 27 00:01:50,240 --> 00:01:55,260 that starts up that's running 24 by seven, like, you know, the CNN newsfeed 28 00:01:55,260 --> 00:01:59,520 or the BBN, you know, newsfeed, something that's going all the time, and 29 00:01:59,520 --> 00:02:01,540 it might not even be anybody watching it. 30 00:02:01,540 --> 00:02:04,840 So, the registration process could happen first, and then the receivers 31 00:02:04,840 --> 00:02:06,300 could join later. 32 00:02:06,300 --> 00:02:10,800 So, just to simplify things, I'm going to start with the first scenario 33 00:02:10,800 --> 00:02:16,220 where the receiver joins first, and then the video starts up after that. 34 00:02:16,220 --> 00:02:20,780 So, just as a review, step number one in this process is if the receiver 35 00:02:20,780 --> 00:02:24,480 is joining, we know that receiver, we're just going to assume IPv4 for 36 00:02:24,480 --> 00:02:26,020 now just to keep it simple. 37 00:02:26,020 --> 00:02:29,620 We know that receiver, which is my laptop here on the left, is going to 38 00:02:29,620 --> 00:02:31,740 send what? Review question. 39 00:02:31,740 --> 00:02:36,120 What kind of IgMP message will that receiver send his default gateway 40 00:02:36,120 --> 00:02:39,420 saying, I wish to be part of this stream? 41 00:02:39,420 --> 00:02:42,200 Who can answer that? 42 00:02:42,200 --> 00:02:51,360 Well, hopefully the answer you came up with was an IgMP membership report. 43 00:02:51,360 --> 00:02:54,200 Sometimes they call that an IgMP join. 44 00:02:54,200 --> 00:02:58,520 That's the sort of slang term for that, but the technical term is an IgMP 45 00:02:58,520 --> 00:03:00,720 membership report. 46 00:03:00,720 --> 00:03:04,360 And we know that the destination address of that report will be whatever 47 00:03:04,360 --> 00:03:08,700 the stream is that the guy wishes to watch, and also in the body of the 48 00:03:08,700 --> 00:03:12,740 report, the GDA field, the group destination address field, will also 49 00:03:12,740 --> 00:03:15,120 be this exact same thing. 50 00:03:15,120 --> 00:03:22,520 Okay, now if this router here is not enabled for PIM, on that interface, 51 00:03:22,520 --> 00:03:26,840 he's going to ignore that because routers don't listen to IgMP by default. 52 00:03:26,840 --> 00:03:29,700 They ignore it. So, that's one of the reasons why we have to enable PIM 53 00:03:29,700 --> 00:03:34,680 in some form, either dense mode or sparse mode, on this interface, because 54 00:03:34,680 --> 00:03:39,920 that also enables IgMP processing as a byproduct of that. 55 00:03:39,920 --> 00:03:43,320 So, let's just assume for the sake of argument that every single interface 56 00:03:43,320 --> 00:03:48,040 that we see here in this drawing already has PIM sparse mode enabled. 57 00:03:48,040 --> 00:03:49,560 Okay, so let's just assume that. 58 00:03:49,560 --> 00:03:53,040 Also, let's assume for the sake of argument that we've already predetermined 59 00:03:53,040 --> 00:03:58,300 that the PIM rendezvous point is going to be router three right here. 60 00:03:58,300 --> 00:04:03,880 And all of the routers, including router three, are pointing at the IP 61 00:04:03,880 --> 00:04:07,600 address on router three's fast, Ethernet zero zero, which is three dot 62 00:04:07,600 --> 00:04:12,260 four dot three dot three as the PIM RP address. 63 00:04:12,260 --> 00:04:17,920 And in case you forgot, the command for that at the global level was IP 64 00:04:17,920 --> 00:04:25,480 PIM RP dash address, and then you put the address. 65 00:04:25,480 --> 00:04:29,480 And we did that on every single router, including the RP itself. 66 00:04:29,480 --> 00:04:32,640 Okay, so that was the command to statically configure an RP. 67 00:04:32,640 --> 00:04:37,020 Okay, so PIM is enabled. 68 00:04:37,020 --> 00:04:38,840 Everybody knows who the RP is. 69 00:04:38,840 --> 00:04:41,640 And of course, everybody has to be able to reach the RP. 70 00:04:41,640 --> 00:04:44,920 So, we're going to assume there's some sort of routing protocol like EIGRP 71 00:04:44,920 --> 00:04:48,340 or RIP or something, running in the background. 72 00:04:48,340 --> 00:04:51,360 So everybody knows how to get to everything. 73 00:04:51,360 --> 00:04:55,980 Okay, so all of that background prerequisite stuff is already done. 74 00:04:55,980 --> 00:05:00,680 All right, so now the IGMP membership report comes in on router two. 75 00:05:00,680 --> 00:05:06,680 Now, if I did at that moment, right after router two received that IGMP 76 00:05:06,680 --> 00:05:12,100 membership report, if I issued the command show IP em route in router 77 00:05:12,100 --> 00:05:18,520 two, here's a review question, what kind of em route entry would I see? 78 00:05:18,520 --> 00:05:24,600 Exactly. Thank you, Peter. 79 00:05:24,600 --> 00:05:27,380 And for those of you watching, hopefully you said you would see a star 80 00:05:27,380 --> 00:05:29,460 comma G entry. Exactly. 81 00:05:29,460 --> 00:05:31,780 That's why I would see a star comma G. 82 00:05:31,780 --> 00:05:35,540 So in this particular case, if I write that, I'll just keep this here 83 00:05:35,540 --> 00:05:37,700 in red to denote PIM stuff. 84 00:05:37,700 --> 00:05:45,660 So in router two, I would see a star comma 239.999 entry, which is what 85 00:05:45,660 --> 00:05:47,320 we call star comma G. 86 00:05:47,320 --> 00:05:51,220 Now next to that would be the RP's address of 3433. 87 00:05:51,220 --> 00:05:54,640 That indicates that we actually know who the RP is. 88 00:05:54,640 --> 00:05:56,500 Okay, another review question. 89 00:05:56,500 --> 00:06:02,440 Using this particular drawing is our guideline and assuming that the fast 90 00:06:02,440 --> 00:06:07,020 Ethernet links are a much better routing metric than the serial link, 91 00:06:07,020 --> 00:06:12,360 that the serial is really the last preferred route to get anywhere. 92 00:06:12,360 --> 00:06:14,540 And I'm mentioning that for a reason. 93 00:06:14,540 --> 00:06:19,060 In the star comma G entry, we'd have something called an incoming interface. 94 00:06:19,060 --> 00:06:21,540 I'm just going to shorten that to IIF. 95 00:06:21,540 --> 00:06:34,200 On router two, what interface would we see as the incoming interface? 96 00:06:34,200 --> 00:06:37,740 That's right. It would be fast Ethernet zero slash one. 97 00:06:37,740 --> 00:06:40,400 And if you forgot, if you said, well, how did you come up with that? 98 00:06:40,400 --> 00:06:45,100 Remember with the star comma G entry, that's all based around the rendezvous 99 00:06:45,100 --> 00:06:47,800 point. Who is the rendezvous point? 100 00:06:47,800 --> 00:06:49,980 How do we get to the rendezvous point? 101 00:06:49,980 --> 00:06:54,220 And in this particular case, in this diagram, it's a pretty safe bet that 102 00:06:54,220 --> 00:06:57,640 for router two to get to the rendezvous point, his best path is via fast 103 00:06:57,640 --> 00:06:59,840 Ethernet zero slash one. 104 00:06:59,840 --> 00:07:03,500 So let's say that, fast Ethernet zero slash one. 105 00:07:03,500 --> 00:07:04,980 Okay, next question. 106 00:07:04,980 --> 00:07:08,580 There would also be right there something called an RPF neighbor. 107 00:07:08,580 --> 00:07:13,500 What IP address will be listed there in the RPF neighbor field? 108 00:07:13,500 --> 00:07:26,480 Yeah, it would be the IP address of his upstream neighbor, which in this 109 00:07:26,480 --> 00:07:27,980 case is router eight. 110 00:07:27,980 --> 00:07:32,960 Now remember the upstream neighbor in relation to how I get to the rendezvous 111 00:07:32,960 --> 00:07:38,080 point. So that would be eight dot four dot eight dot eight, which is not 112 00:07:38,080 --> 00:07:41,320 eight dot four, eight dot two dot eight dot eight. 113 00:07:41,320 --> 00:07:46,180 So that is router two is upstream neighbor router eight to get to the 114 00:07:46,180 --> 00:07:47,740 rendezvous point. 115 00:07:47,740 --> 00:07:53,260 Last thing, there would also be something in here called an outgoing interface 116 00:07:53,260 --> 00:07:58,700 list. What interface, if any, would be in the outgoing interface list 117 00:07:58,700 --> 00:08:10,020 right now? Yeah, so hopefully said, well, that would be the interface 118 00:08:10,020 --> 00:08:12,940 that received the membership report. 119 00:08:12,940 --> 00:08:17,080 The interface where if we actually received the the multicast where we're 120 00:08:17,080 --> 00:08:17,640 going to send it. 121 00:08:17,640 --> 00:08:22,240 In this particular case, this whole star, G entry was created because 122 00:08:22,240 --> 00:08:24,580 we received a request. 123 00:08:24,580 --> 00:08:29,380 We received an IGMP membership report on fast Ethernet zero zero. 124 00:08:29,380 --> 00:08:33,740 So that's what's going to be in our outgoing interface list, because that's 125 00:08:33,740 --> 00:08:35,220 where receiver has joined. 126 00:08:35,220 --> 00:08:39,380 Okay, so that all happens in a split second as soon as that membership 127 00:08:39,380 --> 00:08:40,920 report comes in. 128 00:08:40,920 --> 00:08:48,600 Then that triggers R2 to generate and transmit a special kind of PIM message. 129 00:08:48,600 --> 00:08:52,180 What do we call that kind of PIM message? 130 00:08:52,180 --> 00:09:02,680 Well, hopefully you answered that is called a PIM join. 131 00:09:02,680 --> 00:09:05,060 So that's the sort of generic term. 132 00:09:05,060 --> 00:09:08,720 But we also talked about there were actually two different kinds of PIM 133 00:09:08,720 --> 00:09:12,980 joins. They take the same packet format, but due to the the presence or 134 00:09:12,980 --> 00:09:16,820 lack of certain flags, there was two different kinds of joins. 135 00:09:16,820 --> 00:09:20,500 What kind of join is R2 going to generate? 136 00:09:20,500 --> 00:09:31,380 So hopefully you said Keith, that's going to be a star, G join, a PIM 137 00:09:31,380 --> 00:09:36,360 star, G join exactly, because R2 doesn't know the source. 138 00:09:36,360 --> 00:09:39,080 So in that join, there's going to be a little flag called the wild card 139 00:09:39,080 --> 00:09:43,700 flag, which means I don't know what the source is. 140 00:09:43,700 --> 00:09:48,760 And of all the interfaces that R2 has, which interface will be used to 141 00:09:48,760 --> 00:09:51,900 actually transmit that star, G join? 142 00:09:51,900 --> 00:10:01,540 Where will it go? 143 00:10:01,540 --> 00:10:06,460 That's right. So that the intention of that star, G join is to send it 144 00:10:06,460 --> 00:10:09,560 eventually to make it to the rendezvous point. 145 00:10:09,560 --> 00:10:12,320 We want to let the rendezvous point know, hey, we've got somebody who 146 00:10:12,320 --> 00:10:13,500 is interested here. 147 00:10:13,500 --> 00:10:15,700 And yes, you guys in the live stream, you're answering correctly. 148 00:10:15,700 --> 00:10:19,780 It's all based on basically two things, the incoming interface, which 149 00:10:19,780 --> 00:10:23,740 is the interface I used to get to the rendezvous point and to the RPF 150 00:10:23,740 --> 00:10:26,560 neighbor. So in this particular case, it's going to actually be transmitted 151 00:10:26,560 --> 00:10:29,780 out on fast Ethan at zero slash one. 152 00:10:29,780 --> 00:10:34,520 And then because we know our RPF neighbors 8.2.8.8, we'll look in our 153 00:10:34,520 --> 00:10:38,300 ARP table, we'll figure out what the the MAC addresses of that guy. 154 00:10:38,300 --> 00:10:44,160 And that's how next question, actually, this is a review question. 155 00:10:44,160 --> 00:10:48,440 What will be the destination MAC address of this ethernet frame that's 156 00:10:48,440 --> 00:11:08,500 carrying this PIM star, G join? 157 00:11:08,500 --> 00:11:10,700 Well, this one was a little tricky. 158 00:11:10,700 --> 00:11:16,060 This is a little tricky because the star, G join at layer three of the 159 00:11:16,060 --> 00:11:20,960 networking layer goes to the exact same destination IP address as PIM 160 00:11:20,960 --> 00:11:25,760 hellows. 224 00 13. 161 00:11:25,760 --> 00:11:29,180 So now that we know that the layer three destination is a multicast address, 162 00:11:29,180 --> 00:11:32,580 that should cue you in that, ah, okay, if the layer three destination 163 00:11:32,580 --> 00:11:38,280 address is a multicast address, then we can derive the layer two destination 164 00:11:38,280 --> 00:11:42,700 MAC address from that multicast address. 165 00:11:42,700 --> 00:11:46,540 So in the very beginning of the videos yesterday, I said that all IPB4 166 00:11:46,540 --> 00:11:51,720 multicasts go to the address of 0100 5E. 167 00:11:51,720 --> 00:11:56,540 And then I said, basically, you map the last 23 bits down into the MAC 168 00:11:56,540 --> 00:12:02,700 address here. Well, 13 in hex is what 10, 11, 12, 13, ABCD. 169 00:12:02,700 --> 00:12:13,340 So that's D. So I'll be 0100 5E, 0000 D. 170 00:12:13,340 --> 00:12:22,560 If I got that right there, 0100 5E, and then D is, yep, D is 13, ABCD, 171 00:12:22,560 --> 00:12:27,320 10, 11, 12, 13. So that will actually be the destination MAC address of 172 00:12:27,320 --> 00:12:31,420 that star, G join, because it's going to a multicast. 173 00:12:31,420 --> 00:12:38,480 In the actual IP header, what's going to be the time to live in that IP 174 00:12:38,480 --> 00:12:47,060 header for that join? 175 00:12:47,060 --> 00:12:49,720 That's right. It's going to be one. 176 00:12:49,720 --> 00:12:54,020 Remember, we talked about how multicast addresses have different scopes. 177 00:12:54,020 --> 00:12:57,040 And we said, according to the Internet Assigned Numbers Authority, any 178 00:12:57,040 --> 00:13:02,800 multicast address that begins with 22400 is called the link local scope, 179 00:13:02,800 --> 00:13:06,200 which means it should have just a time to live of one. 180 00:13:06,200 --> 00:13:09,900 It's only meant for your next hop neighbor. 181 00:13:09,900 --> 00:13:11,020 So let me ask you this. 182 00:13:11,020 --> 00:13:16,160 If this star comma G join is only meant to be processed by router 8 and 183 00:13:16,160 --> 00:13:28,440 then discarded, how is it ever going to get to the rendezvous point? 184 00:13:28,440 --> 00:13:31,520 Well, router 8 is going to have to replicate it. 185 00:13:31,520 --> 00:13:34,280 Exactly. He's going to have to create a new one himself. 186 00:13:34,280 --> 00:13:39,080 So basically, the join coming from router 2, the source address will be, 187 00:13:39,080 --> 00:13:43,200 in this case, 8.2.8.2, router 2 source address. 188 00:13:43,200 --> 00:13:46,620 The destination will be 2240013. 189 00:13:46,620 --> 00:13:49,900 Router 8 will process that in his CPU. 190 00:13:49,900 --> 00:13:52,780 His CPU will say, oh, this is a star comma G join. 191 00:13:52,780 --> 00:13:57,400 It's got the RP bit set, which means it needs to be forwarded up to the 192 00:13:57,400 --> 00:13:58,300 rendezvous point. 193 00:13:58,300 --> 00:14:02,520 So router 8 will say, OK, I'm going to use my incoming interface, which 194 00:14:02,520 --> 00:14:05,980 is, he says, oh, oh, so when router 8 gets that, guess what? 195 00:14:05,980 --> 00:14:10,500 That's going to create star comma G state in him, which he didn't have 196 00:14:10,500 --> 00:14:14,360 before. So now he's going to have star comma G state. 197 00:14:14,360 --> 00:14:18,780 It's going to look very similar to what we saw before. 198 00:14:18,780 --> 00:14:25,820 Now, his incoming interface will be fast Ethan at 00.83, because that's 199 00:14:25,820 --> 00:14:29,420 his interface to reach the rendezvous point. 200 00:14:29,420 --> 00:14:40,460 His RPF neighbor is going to actually be 8.3.8.3, and his outgoing interface 201 00:14:40,460 --> 00:14:46,360 list will be the interface that received that PIM star comma G join, which 202 00:14:46,360 --> 00:14:48,660 is fast Ethan at 0 slash 1. 203 00:14:48,660 --> 00:14:52,260 So now that he's created that star comma G state, he says, OK, I need 204 00:14:52,260 --> 00:14:55,720 to now create my own star comma G join. 205 00:14:55,720 --> 00:14:57,300 And there it goes. 206 00:14:57,300 --> 00:15:03,860 PIM star comma G join. 207 00:15:03,860 --> 00:15:09,060 That will also be going to the destination address of 2240013, but this 208 00:15:09,060 --> 00:15:12,840 will have a different source address because it's being sourced from router 209 00:15:12,840 --> 00:15:15,980 8. So if we capture that in a sniffer trace, the source IP address of 210 00:15:15,980 --> 00:15:21,960 that would be 8.3.8.8. 211 00:15:21,960 --> 00:15:25,500 And then once the rendezvous point gets that, now that creates star comma 212 00:15:25,500 --> 00:15:39,220 G state in him. He knows that he's the RP, so you'll see that there. 213 00:15:39,220 --> 00:15:44,780 What will we see in the star comma G state of the incoming interface on 214 00:15:44,780 --> 00:15:54,620 the rendezvous point? 215 00:15:54,620 --> 00:15:58,620 That's right. In this particular case, it will say no, because remember 216 00:15:58,620 --> 00:16:01,940 the incoming interface is the interface that leads to the RP. 217 00:16:01,940 --> 00:16:04,940 Well, if the RP had a split personality and he was psychotic, he might 218 00:16:04,940 --> 00:16:05,980 put something else in there. 219 00:16:05,980 --> 00:16:09,820 But he says, look, I'm normal, I'm okay, I know I'm the RP, I don't use 220 00:16:09,820 --> 00:16:12,340 any interface to get to myself. 221 00:16:12,340 --> 00:16:13,860 So incoming interface is no. 222 00:16:13,860 --> 00:16:19,020 What would we have as the RPF neighbor here? 223 00:16:19,020 --> 00:16:26,860 That's right, it would be 000, 000. 224 00:16:26,860 --> 00:16:31,040 Once again, I don't use any neighbor to get to myself. 225 00:16:31,040 --> 00:16:34,300 And here, the outgoing interface list would be the interface that received 226 00:16:34,300 --> 00:16:36,540 the star comma G join.