1 00:00:08,320 --> 00:00:11,580 So let's start digging a little bit deeper into the details of the pin 2 00:00:11,580 --> 00:00:17,760 bootstrap router protocol, starting with the election process. 3 00:00:17,760 --> 00:00:23,820 So we know that only one router can actually be the bootstrap router, 4 00:00:23,820 --> 00:00:27,160 and it's the bootstrap router's job to let all the other routers know 5 00:00:27,160 --> 00:00:28,980 who the rendezvous points are. 6 00:00:28,980 --> 00:00:32,140 So how is that elected? 7 00:00:32,140 --> 00:00:35,560 Well it's elected by this flooding of bootstrap messages. 8 00:00:35,560 --> 00:00:36,880 We'll actually see this in just a minute. 9 00:00:36,880 --> 00:00:39,600 That's the actual type of PIM message. 10 00:00:39,600 --> 00:00:43,200 So before we've seen PIM registers, we've seen PIM hello's, we've seen 11 00:00:43,200 --> 00:00:47,460 PIM joins. Now we're going to see another type of PIM message in our sniffer 12 00:00:47,460 --> 00:00:49,680 trace called a bootstrap message. 13 00:00:49,680 --> 00:00:55,080 These go out to the same addresses, hello's 2240013. 14 00:00:55,080 --> 00:00:56,960 So it's because it's got that link local scope. 15 00:00:56,960 --> 00:01:01,340 It has to be replicated by each router along the hop so it can get all 16 00:01:01,340 --> 00:01:06,860 the way out. And so the bootstrap router, if there's two or more routers 17 00:01:06,860 --> 00:01:09,040 who are candidate BSRs. 18 00:01:09,040 --> 00:01:11,900 The one that's the winner is either the one with the highest priority, 19 00:01:11,900 --> 00:01:15,760 now the priority is 0 by default, but you can raise that all the way up 20 00:01:15,760 --> 00:01:20,720 to 255 if you want, or the one with the highest IP address. 21 00:01:20,720 --> 00:01:22,680 That will be the winner. 22 00:01:22,680 --> 00:01:26,640 Now with PIM BSR, a preemption is on by default. 23 00:01:26,640 --> 00:01:31,220 So what that means is if I currently have a router serving as my BSR, 24 00:01:31,220 --> 00:01:34,260 and let's say his IP address is 2.2.2.2. 25 00:01:34,260 --> 00:01:37,520 And he's been serving as the BSR for the last six months. 26 00:01:37,520 --> 00:01:41,700 If I put another router into the network, configure him as a candidate 27 00:01:41,700 --> 00:01:47,180 BSR, and his IP address is higher, he will take over the role of being 28 00:01:47,180 --> 00:01:54,140 the BSR. It's not like it sticks with one particular router. 29 00:01:54,140 --> 00:01:57,400 So this is how we configure the candidate BSR. 30 00:01:57,400 --> 00:02:04,640 IPPIM BSR-candidate, and then just like our auto RP, we want to specify 31 00:02:04,640 --> 00:02:09,840 an interface that would be used as the source IP address of our messages. 32 00:02:09,840 --> 00:02:12,480 Then you can specify a hash mask length. 33 00:02:12,480 --> 00:02:14,840 I'll get into that in the very last video here. 34 00:02:14,840 --> 00:02:17,960 We'll talk a little bit about that, but by default at 0. 35 00:02:17,960 --> 00:02:20,540 And then optionally you can specify the priority. 36 00:02:20,540 --> 00:02:25,320 Like I said, the priority is 0 if you leave it alone. 37 00:02:25,320 --> 00:02:29,880 So that's how you configure the candidate BSR. 38 00:02:29,880 --> 00:02:32,900 How do I configure the candidate RPs? 39 00:02:32,900 --> 00:02:36,120 Well, an auto RP, that was, do you remember? 40 00:02:36,120 --> 00:02:40,100 What was the command in auto RP to specify candidate RP? 41 00:02:40,100 --> 00:02:51,080 Well, hopefully the command that came to your mind was IPPIM RP-send-announce. 42 00:02:51,080 --> 00:02:52,700 RP-send-announce. 43 00:02:52,700 --> 00:02:56,320 That's how you configure the candidate RP in the world of auto RP. 44 00:02:56,320 --> 00:03:03,000 Well, in the world of BSR, it's IPPIM RP-candidate. 45 00:03:03,000 --> 00:03:06,760 So I can definitely see this as being a question on some test. 46 00:03:06,760 --> 00:03:10,560 They can give you both ones and say which one is used by auto RP, which 47 00:03:10,560 --> 00:03:12,960 one is used by BSR. 48 00:03:12,960 --> 00:03:15,800 So definitely when I have that straight. 49 00:03:15,800 --> 00:03:16,940 Same thing here. 50 00:03:16,940 --> 00:03:20,060 The RP candidate, you have to specify an interface to say what his source 51 00:03:20,060 --> 00:03:23,600 IP address is going to be. 52 00:03:23,600 --> 00:03:27,380 And at that point, you could just hit enter and leave it alone. 53 00:03:27,380 --> 00:03:31,600 And he will announce his RP candidacy as a candidate for all multicast 54 00:03:31,600 --> 00:03:36,060 groups. But just like auto RP, you could reference an access list to say 55 00:03:36,060 --> 00:03:40,260 which particular groups he's going to announce his candidacy for. 56 00:03:40,260 --> 00:03:43,460 And you can specify a priority. 57 00:03:43,460 --> 00:03:46,920 And I'll talk a little bit more about the priority here in just a little 58 00:03:46,920 --> 00:03:54,020 bit. Now how do I monitor this? 59 00:03:54,020 --> 00:03:57,940 Show IPPIM BSR and show IPPIM RP mapping. 60 00:03:57,940 --> 00:04:02,020 That same command show IPPIM RP mapping is also what we used to monitor 61 00:04:02,020 --> 00:04:04,140 auto RP as well. 62 00:04:04,140 --> 00:04:06,660 So that command works both ways. 63 00:04:06,660 --> 00:04:11,800 Now before I actually configure this and we get it running, let's actually, 64 00:04:11,800 --> 00:04:14,420 well, let's go ahead and do it. 65 00:04:14,420 --> 00:04:18,020 I'll do a snipper trace and then we'll look at that and we'll come back 66 00:04:18,020 --> 00:04:27,180 to these slides here. 67 00:04:27,180 --> 00:04:31,940 All right, so we're going to go into, let's see here. 68 00:04:31,940 --> 00:04:35,840 Let's take off some of our auto RP stuff right now because we don't need 69 00:04:35,840 --> 00:04:46,940 both. So I'm going to start by converting all of my interfaces back to 70 00:04:46,940 --> 00:04:54,060 sparse mode, which does away with all that potential flooding I was concerned 71 00:04:54,060 --> 00:05:20,160 about. 0001. Okay. 72 00:05:20,160 --> 00:05:22,320 What we got here? 73 00:05:22,320 --> 00:05:24,940 This is zero slash zero. 74 00:05:24,940 --> 00:05:33,640 Okay. And this guy here do show run section PIM. 75 00:05:33,640 --> 00:05:38,900 Let's get rid of this because we're not doing auto RP anymore. 76 00:05:38,900 --> 00:05:55,080 Okay, let's go to router eight. 77 00:05:55,080 --> 00:05:58,380 And right now this guy I believe is configures our mapping agent. 78 00:05:58,380 --> 00:06:02,820 So let's get rid of that because that's for auto RP. 79 00:06:02,820 --> 00:06:20,120 Now we just have to go to router four. 80 00:06:20,120 --> 00:06:23,560 Okay, so everybody's configured at this point. 81 00:06:23,560 --> 00:06:29,160 We're back to sparse mode, but we haven't configured any BSR stuff yet. 82 00:06:29,160 --> 00:06:34,000 So let's start by configuring, let's see here. 83 00:06:34,000 --> 00:06:41,120 Why don't we have router four and router eight both contend to be BSR. 84 00:06:41,120 --> 00:06:48,100 So we'll configure both routers as candidate BSRs. 85 00:06:48,100 --> 00:06:52,300 And we'll just rely on, we'll use priority to make the decision about 86 00:06:52,300 --> 00:06:53,140 who the winner is. 87 00:06:53,140 --> 00:06:57,620 So I will give router four the higher priority than router eight. 88 00:06:57,620 --> 00:07:00,460 On router eight I won't even configure the priority at all. 89 00:07:00,460 --> 00:07:03,220 So let's start with router four since we're here. 90 00:07:03,220 --> 00:07:08,100 IP PIM BSR dash candidate. 91 00:07:08,100 --> 00:07:13,180 And we'll just select, I don't know, serial zero slash one slash zero 92 00:07:13,180 --> 00:07:16,240 as a source IP address. 93 00:07:16,240 --> 00:07:18,360 We'll leave the default hash mask. 94 00:07:18,360 --> 00:07:21,940 And notice that if you want to get to the priority, you have to specify 95 00:07:21,940 --> 00:07:25,780 the hash mask. Now I know that right now you're saying what is a hash 96 00:07:25,780 --> 00:07:27,360 mask? You haven't explained that yet. 97 00:07:27,360 --> 00:07:29,500 Well, we'll get to that. 98 00:07:29,500 --> 00:07:37,140 But now I'm going to do the priority list, do a priority of 40. 99 00:07:37,140 --> 00:07:40,540 Okay, and before I do any of this stuff I want to start doing some sniffer 100 00:07:40,540 --> 00:07:50,940 traces here. So let's just capture on, what do we want to capture here? 101 00:07:50,940 --> 00:07:59,540 Our four's fastestion at zero zero, which is zero seven on the switch. 102 00:07:59,540 --> 00:08:04,700 Okay, anything that goes in or out of that. 103 00:08:04,700 --> 00:08:11,200 How about our eight zero zero and zero one? 104 00:08:11,200 --> 00:08:19,860 That's going to be zero two and zero thirteen. 105 00:08:19,860 --> 00:08:24,600 And that should do it. 106 00:08:24,600 --> 00:08:29,440 Let's see here. And we're going to have router three be the candidate 107 00:08:29,440 --> 00:08:32,980 RP. I'm already capturing on zero zero so that should capture his messages 108 00:08:32,980 --> 00:08:35,540 as well when we get around to him. 109 00:08:35,540 --> 00:08:38,020 All right, so let's go to the switch here. 110 00:08:38,020 --> 00:08:40,600 Before I do this. 111 00:08:40,600 --> 00:09:00,200 Let's go to the switch. 112 00:09:00,200 --> 00:09:03,820 Okay, so it's going to be zero slash two, fastestion at zero slash seven 113 00:09:03,820 --> 00:09:10,220 and fastestion at zero slash thirteen. 114 00:09:10,220 --> 00:09:26,440 Okay, so let's go back to router four. 115 00:09:26,440 --> 00:09:41,660 Okay, let's start the sniffer trace. 116 00:09:41,660 --> 00:09:45,180 Okay, so we can see a whole bunch of bootstrap messages. 117 00:09:45,180 --> 00:09:48,100 And the reason why we're seeing a lot of these is because I'm capturing 118 00:09:48,100 --> 00:09:51,200 on multiple interfaces so we're seeing them coming in. 119 00:09:51,200 --> 00:09:52,740 We're seeing them going out. 120 00:09:52,740 --> 00:09:55,740 We're seeing them being forwarded. 121 00:09:55,740 --> 00:09:58,320 It's really just one message though. 122 00:09:58,320 --> 00:10:04,520 So if I open it up a little bit. 123 00:10:04,520 --> 00:10:09,660 So notice it's carried in PIM because this is another PIM message type, 124 00:10:09,660 --> 00:10:11,600 message type four bootstrap. 125 00:10:11,600 --> 00:10:17,740 And it's pretty simple in this case. 126 00:10:17,740 --> 00:10:20,740 He's saying that this is the bootstrap router. 127 00:10:20,740 --> 00:10:22,060 I wish to be the bootstrap router. 128 00:10:22,060 --> 00:10:24,500 This is router four right now, two dot four dot two dot four. 129 00:10:24,500 --> 00:10:29,480 And we've given him a priority of forty. 130 00:10:29,480 --> 00:10:35,680 And now we'll go ahead and configure a similar command on router eight. 131 00:10:35,680 --> 00:10:39,180 But we'll just give him a lower priority. 132 00:10:39,180 --> 00:10:51,220 We'll just leave him like that. 133 00:10:51,220 --> 00:10:55,080 So now they're both sending out BSR messages and they will continue to 134 00:10:55,080 --> 00:10:57,900 do so. It's not like one is going to stop. 135 00:10:57,900 --> 00:11:02,580 In the world of some protocols like spanning tree, for example, once everybody 136 00:11:02,580 --> 00:11:06,220 knows who the root bridge is, it's just the root bridge's job to send 137 00:11:06,220 --> 00:11:09,700 out BPDUs periodically and everybody else is quiet. 138 00:11:09,700 --> 00:11:12,760 Not so with BSR. 139 00:11:12,760 --> 00:11:18,240 In this particular case, let's just keep capturing a few of these here. 140 00:11:18,240 --> 00:11:27,220 That's probably enough. 141 00:11:27,220 --> 00:11:29,440 We didn't get any bootstrap messages yet. 142 00:11:29,440 --> 00:11:32,740 Let's keep going. 143 00:11:32,740 --> 00:11:48,100 Okay, here's some bootstrap messages. 144 00:11:48,100 --> 00:11:51,620 Two four, two four, two four. 145 00:11:51,620 --> 00:12:02,120 So what's happening in this particular case is that it looks like we missed, 146 00:12:02,120 --> 00:12:07,420 I didn't capture the bootstrap message that was sent from router eight. 147 00:12:07,420 --> 00:12:11,540 But it's quite possible that as soon as I hit the command on router eight, 148 00:12:11,540 --> 00:12:16,420 before he even had a chance to create his own bootstrap message, he may 149 00:12:16,420 --> 00:12:20,260 have received the incoming bootstrap message from router four, and he 150 00:12:20,260 --> 00:12:22,980 may have just realized, oh, router four is better than me. 151 00:12:22,980 --> 00:12:27,240 He's got a higher priority than me, so I'm not even going to create my 152 00:12:27,240 --> 00:12:29,880 own. I will just forward his. 153 00:12:29,880 --> 00:12:37,420 So all of these have router four's name or ID in the BSR field. 154 00:12:37,420 --> 00:12:39,600 But I could change that. 155 00:12:39,600 --> 00:12:43,160 Actually, let's go to router eight and give him a priority of 50, and 156 00:12:43,160 --> 00:12:50,880 we'll see how that changes over. 157 00:12:50,880 --> 00:12:56,860 All right, let's start it again. 158 00:12:56,860 --> 00:13:01,560 Come on, wire shark. 159 00:13:01,560 --> 00:13:04,580 All right, and all those fails. 160 00:13:04,580 --> 00:13:37,800 Start it over. Okay. 161 00:13:37,800 --> 00:13:40,620 Now I can't even stop the snipper trace. 162 00:13:40,620 --> 00:13:44,760 Nice. There we go. 163 00:13:44,760 --> 00:13:51,420 Okay, so here we see the bootstrap router is being advertised as eight 164 00:13:51,420 --> 00:13:52,940 dot two dot eight dot eight. 165 00:13:52,940 --> 00:13:57,500 Now, because I'm capturing on multiple interfaces, we don't really know 166 00:13:57,500 --> 00:14:03,740 if this is the bootstrap message that originated on router eight, or if 167 00:14:03,740 --> 00:14:05,260 this is just one that was fine. 168 00:14:05,260 --> 00:14:07,580 So we're forwarded by another router. 169 00:14:07,580 --> 00:14:18,620 But we don't even see here is a, well, here's router four, three dot four 170 00:14:18,620 --> 00:14:19,560 dot three dot four. 171 00:14:19,560 --> 00:14:21,400 That's the IP address of router four. 172 00:14:21,400 --> 00:14:25,280 So based on the fact that that's his source address, we can see he is 173 00:14:25,280 --> 00:14:30,320 forwarding the bootstrap message from router eight. 174 00:14:30,320 --> 00:14:33,720 So we don't even see the bootstrap message from router four anymore. 175 00:14:33,720 --> 00:14:37,780 He's taken his name out of there, and everybody now realizes that router 176 00:14:37,780 --> 00:14:41,600 eight is the BSR, by virtue of the higher priority. 177 00:14:41,600 --> 00:14:46,520 Now the last piece of the puzzle here is to make a router a candidate 178 00:14:46,520 --> 00:14:55,740 RP. So we'll just go back to our friend router three. 179 00:14:55,740 --> 00:15:04,940 And we'll do that IPPIM RP-Canada, fast ethernet zero slash one. 180 00:15:04,940 --> 00:15:10,020 And I'm not going to change the priority or anything like that. 181 00:15:10,020 --> 00:15:15,840 I will change the interval so they go out more frequently. 182 00:15:15,840 --> 00:15:30,700 Let's start this up again. 183 00:15:30,700 --> 00:15:46,260 Okay, so this is what I wanted to point out. 184 00:15:46,260 --> 00:15:49,120 There we go. Okay. 185 00:15:49,120 --> 00:15:59,740 So a router serving as the RP candidate in PIMBSR won't even talk. 186 00:15:59,740 --> 00:16:03,820 He won't even send an RP advertisement, and we see it here, it's called 187 00:16:03,820 --> 00:16:05,340 an RP candidate. 188 00:16:05,340 --> 00:16:07,460 Candidate RP advertisement. 189 00:16:07,460 --> 00:16:11,940 He won't even send that until he knows who the bootstrap router is. 190 00:16:11,940 --> 00:16:13,900 Now why is that? 191 00:16:13,900 --> 00:16:16,120 Well because, take a look at this message. 192 00:16:16,120 --> 00:16:18,740 This is not multicast. 193 00:16:18,740 --> 00:16:20,720 This is unicast. 194 00:16:20,720 --> 00:16:25,160 So the candidate RP's, once they know who the BSR is, they actually send 195 00:16:25,160 --> 00:16:29,960 a unicast RP advertisement directly to the BSR. 196 00:16:29,960 --> 00:16:34,800 And clearly they could not do that if they didn't know beforehand who 197 00:16:34,800 --> 00:16:40,780 the BSR is. So here he's sending it to the BSR. 198 00:16:40,780 --> 00:16:43,040 And we can see he says, here's my name. 199 00:16:43,040 --> 00:16:47,060 I want to be the RP for everything. 200 00:16:47,060 --> 00:16:57,640 And then... So let's see here was the very first one. 201 00:16:57,640 --> 00:17:03,020 And so this now, so now our bootstrap message from the BSR not only contains 202 00:17:03,020 --> 00:17:08,380 his identifier, his name, but also contains that information about that 203 00:17:08,380 --> 00:17:10,620 rendezvous point. 204 00:17:10,620 --> 00:17:15,060 Now before I go a little bit further, let's go back to the slides because 205 00:17:15,060 --> 00:17:17,820 I don't want to get too far ahead of myself. 206 00:17:17,820 --> 00:17:27,280 Okay, so we've seen that the BSR send what's called bootstrap messages. 207 00:17:27,280 --> 00:17:31,140 Now here's a big difference between this and auto RP. 208 00:17:31,140 --> 00:17:36,380 In the world of auto RP, the mapping agent was responsible for collecting 209 00:17:36,380 --> 00:17:41,200 all of the RP announced messages and the mapping agent elected the best 210 00:17:41,200 --> 00:17:43,480 RP for any given group. 211 00:17:43,480 --> 00:17:46,820 So all the other routers out there, they didn't necessarily know the full 212 00:17:46,820 --> 00:17:51,060 range of RP's. All they knew about was the RP's that the mapping agent 213 00:17:51,060 --> 00:17:55,500 had elected. PIMBSR is not like that. 214 00:17:55,500 --> 00:18:01,920 In PIMBSR, the idea is all of the RP's unicastor information to the BSR, 215 00:18:01,920 --> 00:18:07,300 the BSR gathers them all into a combined list in that bootstrap message 216 00:18:07,300 --> 00:18:08,520 and then he sends it out. 217 00:18:08,520 --> 00:18:13,760 So every router in the network knows about every single BSR. 218 00:18:13,760 --> 00:18:17,980 Not every single BSR, every single rendezvous point. 219 00:18:17,980 --> 00:18:22,320 So if I'm a router sitting somewhere in the network and I say, okay, I've 220 00:18:22,320 --> 00:18:26,520 just received a bootstrap message from the BSR and inside there, there's 221 00:18:26,520 --> 00:18:32,300 a list of four different rendezvous points, all servicing the exact same 222 00:18:32,300 --> 00:18:35,880 group. Well, we know that our, that PIM can't do that. 223 00:18:35,880 --> 00:18:37,720 PIM can only use one. 224 00:18:37,720 --> 00:18:42,020 So instead of like an auto RP where one router made that decision, the 225 00:18:42,020 --> 00:18:45,020 mapping agent said, I'm going to tell you who you should use. 226 00:18:45,020 --> 00:18:48,560 In this case, it's up to every router individually. 227 00:18:48,560 --> 00:18:51,660 Every router when they receive these incoming bootstrap messages, if they 228 00:18:51,660 --> 00:18:55,400 see two or more routers in there servicing the same group, each router 229 00:18:55,400 --> 00:19:01,020 will independently elect for themselves which RP they want to use for 230 00:19:01,020 --> 00:19:02,640 any given group. 231 00:19:02,640 --> 00:19:05,140 Now, I'll go into more details about that in a little bit, but we saw 232 00:19:05,140 --> 00:19:11,500 a little bit of a, a little bit of a preview of that because when we looked 233 00:19:11,500 --> 00:19:14,120 at our, let's go back. 234 00:19:14,120 --> 00:19:16,360 Actually, let's go forward a little bit. 235 00:19:16,360 --> 00:19:17,500 So this is the bootstrap message. 236 00:19:17,500 --> 00:19:19,780 We saw that in the snipper trace. 237 00:19:19,780 --> 00:19:24,500 Generated by BSRs goes to 220,000, 13. 238 00:19:24,500 --> 00:19:28,920 Contains a listing of all known rendezvous points. 239 00:19:28,920 --> 00:19:30,480 So the BSR does not discriminate. 240 00:19:30,480 --> 00:19:35,220 He just collects them all, puts them in that bootstrap message. 241 00:19:35,220 --> 00:19:40,640 So notice in this particular message here, and this will save me from 242 00:19:40,640 --> 00:19:41,960 having to do this in the lab. 243 00:19:41,960 --> 00:19:45,540 Notice that in this particular message, the bootstrap router says, okay, 244 00:19:45,540 --> 00:19:48,380 I'm telling you about two BSRs. 245 00:19:48,380 --> 00:19:55,500 So both of these BSRs are servicing the exact same group. 246 00:19:55,500 --> 00:19:58,960 220, you know, the entire multicast range. 247 00:19:58,960 --> 00:20:05,000 So there's two rendezvous points I'm telling you about. 248 00:20:05,000 --> 00:20:10,640 And it says, okay, the priority for the first rendezvous point, 2722 is 249 00:20:10,640 --> 00:20:15,640 20. The priority for the second rendezvous point is 30. 250 00:20:15,640 --> 00:20:17,520 So I think that gives you a little bit of a hint. 251 00:20:17,520 --> 00:20:20,980 In this particular case, priority wins. 252 00:20:20,980 --> 00:20:25,120 The highest priority, so all routers who receive this will elect for themselves 253 00:20:25,120 --> 00:20:30,900 3.7.3.3 as their rendezvous point because it's got the higher priority 254 00:20:30,900 --> 00:20:45,120 than 2.7.2. And I looked this up because I was just curious, you know, 255 00:20:45,120 --> 00:20:48,040 whenever I see sniffer traces, I'm always curious about every single little 256 00:20:48,040 --> 00:20:51,600 field and what it means, not that you probably ever need to know this 257 00:20:51,600 --> 00:20:55,260 for any kind of test or anything, but FRP. 258 00:20:55,260 --> 00:20:58,800 What's that? For those of you like me who like to know this kind of stuff, 259 00:20:58,800 --> 00:21:02,180 that stands for fragment RP count. 260 00:21:02,180 --> 00:21:08,220 What that's referring to is you'd have to have a lot of RPs to make this 261 00:21:08,220 --> 00:21:11,900 happen, but there's a possibility that let's say you've got, I don't know, 262 00:21:11,900 --> 00:21:16,320 100 RPs or 100 potential RPs in your network. 263 00:21:16,320 --> 00:21:22,200 And the full listing of them just won't fit inside of a single bootstrap 264 00:21:22,200 --> 00:21:27,120 message. Well, in that case, that bootstrap message could be fragmented, 265 00:21:27,120 --> 00:21:32,700 put into multiple IP packets, and so the FRP count gives sort of a clue 266 00:21:32,700 --> 00:21:35,940 as to, okay, there's other fragments coming. 267 00:21:35,940 --> 00:21:40,300 There's more RPs than what I'm sending you in just this one bootstrap 268 00:21:40,300 --> 00:21:43,000 message. Look for some other ones as well. 269 00:21:43,000 --> 00:21:46,880 So that's sort of an indicator to the receiving routers about that. 270 00:21:46,880 --> 00:21:50,700 Probably won't see that used very often, because like I said, you'd have 271 00:21:50,700 --> 00:21:52,680 to have a lot of potential RPs. 272 00:21:52,680 --> 00:21:57,480 To fill it up so big that it won't fit into a single packet. 273 00:21:57,480 --> 00:22:08,600 And the fragment tag, that's used by the same thing. 274 00:22:08,600 --> 00:22:13,880 So a fragment tag is sort of like, think about the IP header of an IPv4 275 00:22:13,880 --> 00:22:16,900 packet. There's the ID field, right? 276 00:22:16,900 --> 00:22:20,740 So if that IP packet has to be fragmented, every single fragment will 277 00:22:20,740 --> 00:22:24,280 have the exact same ID number as the original packet. 278 00:22:24,280 --> 00:22:27,440 That way they can all be sort of, when receivers receive these fragments, 279 00:22:27,440 --> 00:22:30,920 they can say, oh, okay, I know this is all part of one coherent whole 280 00:22:30,920 --> 00:22:33,340 packet. This is the same type of thing. 281 00:22:33,340 --> 00:22:37,320 If a bootstrap message has to be fragmented, they will all contain the 282 00:22:37,320 --> 00:22:39,020 same fragment tag. 283 00:22:39,020 --> 00:22:49,960 Okay? Okay, so this is the RP candidate messages. 284 00:22:49,960 --> 00:22:51,460 We looked at that in the snippet trace. 285 00:22:51,460 --> 00:22:54,040 We saw how they are unicasted. 286 00:22:54,040 --> 00:22:56,500 It includes a priority. 287 00:22:56,500 --> 00:23:00,600 Uses PIM as the transport protocol. 288 00:23:00,600 --> 00:23:04,220 So behind the IP header we saw this was carried in PIM. 289 00:23:04,220 --> 00:23:08,600 And once again, here's an example of one of those. 290 00:23:08,600 --> 00:23:14,180 And we already saw this in the wire shark snipper capture. 291 00:23:14,180 --> 00:23:20,700 Now let's go to, at this point, because I have everything configured, 292 00:23:20,700 --> 00:23:29,800 let's go to router two, who has received these bootstrap messages. 293 00:23:29,800 --> 00:23:35,920 And we're going to use the same command we used in auto RP, show IP PIM 294 00:23:35,920 --> 00:23:42,160 RP mapping. And we can see. 295 00:23:42,160 --> 00:23:46,160 It says, now in this case, I only have a single RP, so there's not a lot 296 00:23:46,160 --> 00:23:50,780 here. But if I had configured two or three or four candidate RP, so as 297 00:23:50,780 --> 00:23:51,960 a matter of fact, let's do that. 298 00:23:51,960 --> 00:23:57,140 Because a bootstrap router could also be a candidate RP at the same time. 299 00:23:57,140 --> 00:24:04,760 So let's go to router four and configure him as a candidate RP as well. 300 00:24:04,760 --> 00:24:20,900 RP-candidate. Okay, so now when we go to router two. 301 00:24:20,900 --> 00:24:32,320 Okay, so now we see all the rendezvous points, right? 302 00:24:32,320 --> 00:24:37,600 Because they were all contained in that single bootstrap message. 303 00:24:37,600 --> 00:24:42,460 And it's saying either one of these could be a potential candidate for 304 00:24:42,460 --> 00:24:44,900 the entire multicast range. 305 00:24:44,900 --> 00:24:50,680 Now looking at just this output right now, there's no way for you to predict 306 00:24:50,680 --> 00:24:54,760 just from this command, which router will actually be used. 307 00:24:54,760 --> 00:24:59,380 So if this guy needs to send a register or a join message, is he going 308 00:24:59,380 --> 00:25:02,600 to use two four or two four, or is he going to use eight three, eight 309 00:25:02,600 --> 00:25:05,000 three, because they both have exactly the same priority? 310 00:25:05,000 --> 00:25:07,360 Well, from this, you can't tell.