1 00:00:08,280 --> 00:00:13,540 So in this next segment, I'm just going to do a brief review of IGMP and 2 00:00:13,540 --> 00:00:16,040 MLDP. So what are these? 3 00:00:16,040 --> 00:00:20,700 Well, IGMP stands for the Internet Group Management Protocol. 4 00:00:20,700 --> 00:00:25,060 Like it sounds, there's an IETF for this. 5 00:00:25,060 --> 00:00:29,920 There is an RFC for it, and there's several versions of IGMP versions, 6 00:00:29,920 --> 00:00:31,320 one, two, and three. 7 00:00:31,320 --> 00:00:35,560 Currently, version two is the one that's used in most devices. 8 00:00:35,560 --> 00:00:40,480 And this is the protocol used by receivers, which is your laptop, to indicate 9 00:00:40,480 --> 00:00:43,980 the multicast's interest to directly connected routers. 10 00:00:43,980 --> 00:00:48,040 So in the previous video segment, I said, you send some sort of a unicast 11 00:00:48,040 --> 00:00:51,760 package to a server saying, hey, tell me what shows you've got. 12 00:00:51,760 --> 00:00:53,980 And the server sends a unicast package back to you. 13 00:00:53,980 --> 00:00:58,060 And that's what displays on your laptop this image of, okay, here's the 14 00:00:58,060 --> 00:00:59,680 various different shows. 15 00:00:59,680 --> 00:01:03,320 And I said that when you click on that, you're sending a message to your 16 00:01:03,320 --> 00:01:06,420 router, to your default gateway saying, I want that. 17 00:01:06,420 --> 00:01:08,880 If you ever see it, send it to me. 18 00:01:08,880 --> 00:01:10,480 Well now we know what that message is. 19 00:01:10,480 --> 00:01:14,640 It is IGMP. You're sending an IGMP message to that router, and the router 20 00:01:14,640 --> 00:01:19,560 has to be listening for IGMP so it can now know that, okay, on fast ethernet 21 00:01:19,560 --> 00:01:25,240 00, I've got a receiver down there that wants this show. 22 00:01:25,240 --> 00:01:28,700 So IGMP is used for IPv4. 23 00:01:28,700 --> 00:01:33,520 And for IPv6, the equivalent is the multicast listener discovery protocol. 24 00:01:33,520 --> 00:01:38,980 And what's nice is that MLDP was pretty much built around the same concepts 25 00:01:38,980 --> 00:01:44,320 as IGMP. So if you're familiar with IGMP, if you studied IGMP versions 26 00:01:44,320 --> 00:01:48,360 two and three and you know the message types, you know how it operates, 27 00:01:48,360 --> 00:01:53,820 you know about 90% of what you need to know for MLDP. 28 00:01:53,820 --> 00:01:57,940 So let's just real briefly talk about the IGMP messages and how they're 29 00:01:57,940 --> 00:02:02,740 used because that is going to be very relevant for our multicast routing 30 00:02:02,740 --> 00:02:09,040 discussion. So your membership reports, that is the name of the specific 31 00:02:09,040 --> 00:02:15,000 IGMP messages that your laptop, the receiver, sends upstream to the router. 32 00:02:15,000 --> 00:02:18,860 So for example, if I now have a directory listing on my laptop that gives 33 00:02:18,860 --> 00:02:24,040 me various shows like in Fox news and stuff and I click on CNN, I want 34 00:02:24,040 --> 00:02:28,840 to watch CNN. Well, in the background, my laptop knows that the GDA, the 35 00:02:28,840 --> 00:02:34,160 group destination address for CNN is 239.555. 36 00:02:34,160 --> 00:02:39,740 So my laptop now is going to generate an IGMP membership report. 37 00:02:39,740 --> 00:02:44,600 It's actually going to go to that address of 239.555. 38 00:02:44,600 --> 00:02:47,720 So whatever the show is that I want to see, that will actually be the 39 00:02:47,720 --> 00:02:52,240 destination address in my IGMP packet. 40 00:02:52,240 --> 00:02:56,020 Now you might be wondering, well, wait a second, if I'm a router and I 41 00:02:56,020 --> 00:03:01,380 receive in a packet going to 239.555, how do I distinguish it between 42 00:03:01,380 --> 00:03:07,740 IGMP, which is something I need to process in my CPU versus that being 43 00:03:07,740 --> 00:03:11,400 the actual CNN data stream itself? 44 00:03:11,400 --> 00:03:21,760 It's actually in the IP protocol number. 45 00:03:21,760 --> 00:03:23,960 So that's how the router would tell the difference. 46 00:03:23,960 --> 00:03:27,380 If that multicast comes in and is UDP, he says, oh, I don't have to pay 47 00:03:27,380 --> 00:03:28,300 attention to that. 48 00:03:28,300 --> 00:03:29,680 That's the actual video. 49 00:03:29,680 --> 00:03:34,760 If it comes in with an IP protocol, I think IGMP is protocol two. 50 00:03:34,760 --> 00:03:38,080 I think ICMP is one and IGMP is two. 51 00:03:38,080 --> 00:03:41,460 I might have those two mixed up, but that's how the router knows, oh, 52 00:03:41,460 --> 00:03:43,680 this is something I need to look at. 53 00:03:43,680 --> 00:03:46,580 And then when it goes into the body of the message, it says, oh, this 54 00:03:46,580 --> 00:03:47,980 is a membership report. 55 00:03:47,980 --> 00:03:48,480 There's a receiver. 56 00:03:48,480 --> 00:03:51,900 A receiver who wants to get this show. 57 00:03:51,900 --> 00:03:56,580 Now if we're talking about IGMP version three, that's got a reserved address. 58 00:03:56,580 --> 00:04:02,840 So your laptop then would send an IGMP membership report to 224.00.22. 59 00:04:02,840 --> 00:04:07,320 That is called the all IGMP V3 routers address. 60 00:04:07,320 --> 00:04:13,640 And so routers running IGMP V3 would be listening for that to 224.00.22. 61 00:04:13,640 --> 00:04:17,240 Now, let's say you've done that. 62 00:04:17,240 --> 00:04:21,800 So your laptop is told the router, hey, membership report, if you ever 63 00:04:21,800 --> 00:04:26,360 get packets going to 239 .777, forward them to me. 64 00:04:26,360 --> 00:04:28,000 And I'll say the packets start coming. 65 00:04:28,000 --> 00:04:29,500 They start coming through the internet. 66 00:04:29,500 --> 00:04:32,460 They hit your router on the back of the head, and he starts forwarding 67 00:04:32,460 --> 00:04:34,640 on its interface. 68 00:04:34,640 --> 00:04:40,400 Okay. Well, that stream might be a stream that goes 24 by 7. 69 00:04:40,400 --> 00:04:43,540 It never stops. It just keeps going forever. 70 00:04:43,540 --> 00:04:48,840 And the router has to have some way of knowing, okay, hello, receiver, 71 00:04:48,840 --> 00:04:50,240 are you still out there? 72 00:04:50,240 --> 00:04:52,680 Do you still want this stream? 73 00:04:52,680 --> 00:04:54,780 Because after all, you know, what if that receiver, what if your laptop 74 00:04:54,780 --> 00:04:57,720 was connected to a hub? 75 00:04:57,720 --> 00:04:59,700 And you yanked out the cable. 76 00:04:59,700 --> 00:05:02,500 You physically pulled your ethernet cable out. 77 00:05:02,500 --> 00:05:04,700 You took your laptop and you walked away. 78 00:05:04,700 --> 00:05:08,380 Well, then your laptop did not have any kind of opportunity to tell the 79 00:05:08,380 --> 00:05:09,720 router, hey, I'm done. 80 00:05:09,720 --> 00:05:11,680 Don't need it anymore. 81 00:05:11,680 --> 00:05:14,740 So the router have to have some way of knowing that's happened. 82 00:05:14,740 --> 00:05:18,040 That, hey, there's no receivers anymore who want this. 83 00:05:18,040 --> 00:05:22,600 So the way it does that is by every single, every minute, roughly, every 84 00:05:22,600 --> 00:05:27,200 minute, it sends out another type of an IGMP packet called a general membership 85 00:05:27,200 --> 00:05:33,060 query. And this goes out to the reserved address of 224001. 86 00:05:33,060 --> 00:05:38,160 That's called the all multi -cast hosts address, 224001. 87 00:05:38,160 --> 00:05:42,600 And that's the router's way of saying, hey, is there anybody in the subnet 88 00:05:42,600 --> 00:05:44,600 who's watching anything? 89 00:05:44,600 --> 00:05:47,040 I've got like three or four or five streams. 90 00:05:47,040 --> 00:05:49,120 I'm all sending into the subnet. 91 00:05:49,120 --> 00:05:51,720 Are people still watching it? 92 00:05:51,720 --> 00:05:56,340 And so the idea is, if your laptop is still there, if your receiver is 93 00:05:56,340 --> 00:06:00,060 still there and watching this, when it gets a membership query, it's your 94 00:06:00,060 --> 00:06:03,080 job to send a membership report. 95 00:06:03,080 --> 00:06:04,700 And say, yep, I'm still here. 96 00:06:04,700 --> 00:06:06,100 I still want the stream. 97 00:06:06,100 --> 00:06:09,580 So these queries are going out, reports are coming back, and that's what 98 00:06:09,580 --> 00:06:11,180 keeps the stream refreshed. 99 00:06:11,180 --> 00:06:14,840 That's how the default gateway knows, okay, I still need to keep forwarding 100 00:06:14,840 --> 00:06:20,160 this. Now, in my particular example where I yanked out my laptop and I 101 00:06:20,160 --> 00:06:24,660 walked away, the router would not hear anything from its query. 102 00:06:24,660 --> 00:06:28,560 So routers typically send two, sometimes three queries before they finally 103 00:06:28,560 --> 00:06:31,200 decide, okay, nobody's there. 104 00:06:31,200 --> 00:06:32,920 I'm going to go ahead and stop forwarding the stream. 105 00:06:32,920 --> 00:06:34,880 I'm not going to send it. 106 00:06:34,880 --> 00:06:39,100 Now, ideally, let's say my laptop is still connected to that hub, but 107 00:06:39,100 --> 00:06:41,860 I just decide, oh, my boss just walked in. 108 00:06:41,860 --> 00:06:43,940 I better stop watching the show and get to work. 109 00:06:43,940 --> 00:06:47,720 So I quickly shut down my little video window there and yank out my ear 110 00:06:47,720 --> 00:06:52,520 plugs. Well, when I shut down that video window, my laptop now sends out 111 00:06:52,520 --> 00:06:55,060 an IGMP leave message. 112 00:06:55,060 --> 00:06:59,760 And this is a specific message that says, I am leaving this group. 113 00:06:59,760 --> 00:07:02,400 I am no longer interested in this group. 114 00:07:02,400 --> 00:07:07,060 Now, when the router gets that, the router says, okay, I know that receiver 115 00:07:07,060 --> 00:07:12,500 is leaving, but there might be some other receivers on that same subnet 116 00:07:12,500 --> 00:07:14,520 that still want this. 117 00:07:14,520 --> 00:07:17,500 So rather than just shutting down the stream immediately, I'm going to 118 00:07:17,500 --> 00:07:20,460 send a query out onto that subnet again. 119 00:07:20,460 --> 00:07:23,640 But instead of sending a general query, I'm going to send out what's called 120 00:07:23,640 --> 00:07:25,560 a group specific query. 121 00:07:25,560 --> 00:07:31,380 So instead of sending a general query to 224.001, the router says, I'll 122 00:07:31,380 --> 00:07:31,940 actually send out a general query to 224.001. 123 00:07:31,940 --> 00:07:37,020 And then I'll send out a query to that specific group 239.555 or whatever 124 00:07:37,020 --> 00:07:39,200 it is that you happen to be watching. 125 00:07:39,200 --> 00:07:42,940 And if there's any other receivers are still interested, they need to 126 00:07:42,940 --> 00:07:44,520 send a membership report. 127 00:07:44,520 --> 00:07:49,180 Otherwise, the router will time out the stream and delete it. 128 00:07:49,180 --> 00:07:56,000 So those are the four basic message types that IGMP uses. 129 00:07:56,000 --> 00:08:01,120 Now with MLDP, the multicast listener discovery protocol, once again, 130 00:08:01,120 --> 00:08:07,360 this is for IPv6 now, it's structured very similarly to IGMP. 131 00:08:07,360 --> 00:08:13,300 So MLDP version one was based off of IGMP version two, uses all those 132 00:08:13,300 --> 00:08:14,900 same messages I just showed you. 133 00:08:14,900 --> 00:08:17,720 They've got slightly different names, and I'll tell you the names in just 134 00:08:17,720 --> 00:08:24,480 a second. MLDP version two was based off of IGMP version three. 135 00:08:24,480 --> 00:08:28,280 And by default, Cisco devices support both, but they default to version 136 00:08:28,280 --> 00:08:36,180 two. So with MLDP, instead of having an IGMP query, you have an MLDP query. 137 00:08:36,180 --> 00:08:41,460 Pretty simple. Instead of an IGMP membership report, you have an MLDP 138 00:08:41,460 --> 00:08:45,000 listener report. 139 00:08:45,000 --> 00:08:50,640 Instead of having an IGMP leave, you have an MLDP done message. 140 00:08:50,640 --> 00:08:58,760 Now, most devices actually do MLDP, do MLDP version two. 141 00:08:58,760 --> 00:09:03,260 So this message right here, MLDP done, you might not see that, because 142 00:09:03,260 --> 00:09:07,620 that's in the older version of MLDP, MLDP version one. 143 00:09:07,620 --> 00:09:10,040 And this was similar to the IGMP leave. 144 00:09:10,040 --> 00:09:17,860 So if I've got a laptop that's running MLDP, I'm doing IPv6, and I'm doing 145 00:09:17,860 --> 00:09:24,360 MLDP version two, if I want to stop a stream, if I say look, I'm no longer 146 00:09:24,360 --> 00:09:28,540 interested, then actually what I'm going to send is I'm going to send 147 00:09:28,540 --> 00:09:30,820 an MLDP listener report. 148 00:09:30,820 --> 00:09:37,700 But the way that kind of works is when your laptop sends out an MLDP listener 149 00:09:37,700 --> 00:09:40,040 report, there's two fields in there. 150 00:09:40,040 --> 00:09:43,980 There's a field of what you want to listen to, that's the group address, 151 00:09:43,980 --> 00:09:49,260 like FF0E colon colon seven, whatever the layer three addresses you want 152 00:09:49,260 --> 00:09:53,440 to see. And then there's a field for the source address. 153 00:09:53,440 --> 00:09:57,180 Now, most of the time your laptop doesn't know what the source is, so 154 00:09:57,180 --> 00:09:59,980 that source address would just be left with all zeros. 155 00:09:59,980 --> 00:10:03,160 But right next to the source address is another field, actually it's a 156 00:10:03,160 --> 00:10:09,040 flag called the either include flag or the exclude flag. 157 00:10:09,040 --> 00:10:15,900 And the way that works is when my laptop sends out an MLDP listener report, 158 00:10:15,900 --> 00:10:20,860 I'm going to say here's the group I want, the source, I don't know, 0, 159 00:10:20,860 --> 00:10:21,900 0, 0, 0, 0, 0, and then I'm going to send it to the source address. 160 00:10:21,900 --> 00:10:29,200 And I will say exclude 0, 0, 0, 0, which means I'm excluding nobody. 161 00:10:29,200 --> 00:10:33,440 I'm willing to get this from anybody, don't exclude it from anyone. 162 00:10:33,440 --> 00:10:35,800 What about when I want to leave the stream? 163 00:10:35,800 --> 00:10:56,000 Guess what? I'll say this is the stream I want to leave. 164 00:10:56,000 --> 00:11:00,880 So that's sort of MLDP version two's way of sending a leave. 165 00:11:00,880 --> 00:11:04,100 Instead of sending a leave it sends another report, but it changes the 166 00:11:04,100 --> 00:11:09,360 exclude flag to an include flag and it says include nobody. 167 00:11:09,360 --> 00:11:16,680 And then there's the MLDP multi-cast address specific query, the mask, 168 00:11:16,680 --> 00:11:22,880 M-A-S-Q. That's the exact same thing as an IGMP, the group specific report. 169 00:11:22,880 --> 00:11:26,740 It serves the exact same purpose. 170 00:11:26,740 --> 00:11:33,140 So somebody asked in the live question feed the membership query and membership 171 00:11:33,140 --> 00:11:39,820 reports. Are they like the hello and dead intervals? 172 00:11:39,820 --> 00:11:42,300 You could kind of equate it to that. 173 00:11:42,300 --> 00:11:48,320 I mean, we know that like in the case of routing protocols, something 174 00:11:48,320 --> 00:11:53,180 has to go out every hello interval to let your neighbor know you're still 175 00:11:53,180 --> 00:11:56,420 there. Or spanning tree does that too. 176 00:11:56,420 --> 00:12:00,160 BPDUs go out every hello interval to let you know the root bridge is still 177 00:12:00,160 --> 00:12:06,380 there. So you could sort of equate that to this where the router is sending 178 00:12:06,380 --> 00:12:12,660 out queries every 60 seconds saying is anybody there. 179 00:12:12,660 --> 00:12:17,120 And then the listeners have to, the receivers have to respond back saying 180 00:12:17,120 --> 00:12:21,060 yes. So that's sort of like a give and take of hello messages. 181 00:12:21,060 --> 00:12:23,480 I guess you could give it that analogy. 182 00:12:23,480 --> 00:12:29,220 And the whole time is like the router says okay, if I send out a query, 183 00:12:29,220 --> 00:12:34,160 I've got a certain amount of time that if nobody responds back, I'm going 184 00:12:34,160 --> 00:12:38,400 to send it again and possibly a third time. 185 00:12:38,400 --> 00:12:41,240 And then I will time out the stream. 186 00:12:41,240 --> 00:12:45,040 And that's kind of like a dead interval or a hold interval in the case 187 00:12:45,040 --> 00:12:46,120 of routing protocols. 188 00:12:46,120 --> 00:12:50,120 So yeah, between the router and the receiver, the router and the laptop, 189 00:12:50,120 --> 00:12:52,900 you could sort of equate that to hello and hold times. 190 00:12:52,900 --> 00:12:54,500 That would be an appropriate analogy.