1 00:00:08,480 --> 00:00:10,780 So now, congratulations. 2 00:00:10,780 --> 00:00:13,200 If you've been watching this series from the very beginning, you have 3 00:00:13,200 --> 00:00:16,140 made it to the very last video. 4 00:00:16,140 --> 00:00:19,480 If your head isn't spinning at this point, your eyes aren't glazed over, 5 00:00:19,480 --> 00:00:24,340 good job. So now we're going to do our final thing, which is going back 6 00:00:24,340 --> 00:00:25,680 to the bootstrap router. 7 00:00:25,680 --> 00:00:28,900 And the last video I ended with, well, what if a router has received a 8 00:00:28,900 --> 00:00:30,960 bootstrap message? 9 00:00:30,960 --> 00:00:37,120 It sees multiple RPs in there, all with the same priority, all servicing 10 00:00:37,120 --> 00:00:41,700 or all offering their services for the same range of groups. 11 00:00:41,700 --> 00:00:46,460 How does that individual router decide which one is going to be selected? 12 00:00:46,460 --> 00:00:53,220 So we know that individual routers make that decision. 13 00:00:53,220 --> 00:00:55,620 So here's our other start. 14 00:00:55,620 --> 00:01:00,300 Whoever has the lowest priority wins. 15 00:01:00,300 --> 00:01:03,700 And if the priority is the same, a hash function is performed. 16 00:01:03,700 --> 00:01:07,800 And this is where it gets really sort of complex. 17 00:01:07,800 --> 00:01:14,120 So remember how when I was configuring the candidate BSR, that there was 18 00:01:14,120 --> 00:01:17,940 a field in there that sort of glossed over that was called the hash mask 19 00:01:17,940 --> 00:01:21,880 length. And I said the default was zero. 20 00:01:21,880 --> 00:01:26,560 Well, that is specifically for use in this scenario. 21 00:01:26,560 --> 00:01:29,080 So let's talk about that. 22 00:01:29,080 --> 00:01:32,220 So before I go to the next slide, just keep in mind this bullet point 23 00:01:32,220 --> 00:01:37,960 right here. With a default hash mask length of zero, a single rendezvous 24 00:01:37,960 --> 00:01:43,200 point will always be selected for every group destination address. 25 00:01:43,200 --> 00:01:50,440 So what that's saying is, by default, these rendezvous everything in the 26 00:01:50,440 --> 00:01:53,100 class D range, I want to do it. 27 00:01:53,100 --> 00:01:58,520 So if I've learned about, let's say, four rendezvous points who are all 28 00:01:58,520 --> 00:02:02,780 like that in my bootstrap message, with a hash mask length of zero that 29 00:02:02,780 --> 00:02:07,460 I've learned from the BSR, I, as an individual router, will only select 30 00:02:07,460 --> 00:02:12,440 one of those RPs from the list, and I will use him for everything. 31 00:02:12,440 --> 00:02:17,720 By changing that number from a zero to something else, it gives you the 32 00:02:17,720 --> 00:02:19,880 ability to do a little bit of load balance in. 33 00:02:19,880 --> 00:02:23,140 For example, by changing that number to something else, your local router 34 00:02:23,140 --> 00:02:33,060 could say, okay, for the group range of 225.001 through 225.008, I will 35 00:02:33,060 --> 00:02:35,260 select RP number one. 36 00:02:35,260 --> 00:02:42,020 For 225.009 through 225.012, I'll select RP number two. 37 00:02:42,020 --> 00:02:47,600 That can happen by modifying your hash mask length on the BSR itself. 38 00:02:47,600 --> 00:02:51,500 But if you leave at the default of zero, only a single RP will be used 39 00:02:51,500 --> 00:02:53,540 for everything. And maybe you don't care. 40 00:02:53,540 --> 00:02:57,080 Maybe that's fine for you. 41 00:02:57,080 --> 00:03:04,600 Okay, so I'm just putting this in here as sort of a reference. 42 00:03:04,600 --> 00:03:10,520 The algorithm is really just kind of nasty and complex, but here's basically 43 00:03:10,520 --> 00:03:18,780 the idea, is that when a router receives a bootstrap message, if you see 44 00:03:18,780 --> 00:03:21,980 two RPs in there, let's just take two as an example. 45 00:03:21,980 --> 00:03:25,420 Two RPs that have the same weight, the same priority, they're both saying, 46 00:03:25,420 --> 00:03:27,560 I want to be the RP for the exact same group. 47 00:03:27,560 --> 00:03:29,520 Okay, here's what this local router is going to do. 48 00:03:29,520 --> 00:03:32,640 He's going to create a hash, which is a long number. 49 00:03:32,640 --> 00:03:35,580 He's going to do that by his going to say, okay, I'm going to take the 50 00:03:35,580 --> 00:03:38,360 group number that you guys are saying you want to do. 51 00:03:38,360 --> 00:03:43,360 I'm going to take your name, your IP address, and I'm going to take the 52 00:03:43,360 --> 00:03:48,440 hash mask length that was supplied via the BSR up a little higher in that 53 00:03:48,440 --> 00:03:51,240 message. And I'm going to combine all that stuff into this really complex 54 00:03:51,240 --> 00:03:54,900 formula, and that's going to spit out this number, this hash value. 55 00:03:54,900 --> 00:04:01,400 Whoever ends up with the highest hash, that's the one I'm going to select. 56 00:04:01,400 --> 00:04:09,260 Now, it's very unlikely that two RPs will hash to the exact same number, 57 00:04:09,260 --> 00:04:14,100 but if that theoretically happened, which is theoretically possible, whichever 58 00:04:14,100 --> 00:04:17,760 RP had the highest IP address would be the winner. 59 00:04:17,760 --> 00:04:21,460 Okay, so what does this all really translate to? 60 00:04:21,460 --> 00:04:23,540 First of all, how can I tell who's the winner? 61 00:04:23,540 --> 00:04:28,020 Because when I went back to, let's go back to this command here, show 62 00:04:28,020 --> 00:04:34,520 IP PIM mapping, didn't tell me, it just said, okay, these are the potential 63 00:04:34,520 --> 00:04:36,620 RPs I could use. 64 00:04:36,620 --> 00:04:40,080 Well, here's a really nice command you can use to actually figure out, 65 00:04:40,080 --> 00:04:43,760 even before the multicast happens, you might say, well, if the multicast 66 00:04:43,760 --> 00:04:52,240 of, oh, let's say 228.8.8 ever happens in the future, which are PMI going 67 00:04:52,240 --> 00:04:55,440 to use? What, who's going to have the highest hash? 68 00:04:55,440 --> 00:05:03,160 Well, you can use this nice command for that, show IP PIM RP dash hash. 69 00:05:03,160 --> 00:05:06,160 And then the number, like for example, for this particular group, 228 70 00:05:06,160 --> 00:05:14,300 .70.87.65, you can see that 2.7.22, he ended up with a slightly higher 71 00:05:14,300 --> 00:05:17,560 hash value than 3733. 72 00:05:17,560 --> 00:05:23,900 So 2722 will be selected as the rendezvous point for this particular group. 73 00:05:23,900 --> 00:05:26,140 Let's do that over here on my real router. 74 00:05:26,140 --> 00:05:30,920 Show IP PIM RP dash hash. 75 00:05:30,920 --> 00:05:34,360 Let's just pick a number, 227.777. 76 00:05:34,360 --> 00:05:41,300 And you can see here that 2424 will be the winner. 77 00:05:41,300 --> 00:05:43,320 He's got the larger hash value. 78 00:05:43,320 --> 00:05:57,740 Now, any number I put into this command should always result to 2424 being 79 00:05:57,740 --> 00:06:00,980 the winner. It shouldn't really matter. 80 00:06:00,980 --> 00:06:04,040 Yep, he's the winner for that. 81 00:06:04,040 --> 00:06:08,200 Yep, he's the winner for that. 82 00:06:08,200 --> 00:06:12,540 So you can see he's pretty much hashing to the exact same value. 83 00:06:12,540 --> 00:06:17,920 Because what this hash mask length refers to, it's kind of like a subnet 84 00:06:17,920 --> 00:06:19,940 mask or a wildcard mask. 85 00:06:19,940 --> 00:06:24,020 And what it's masking is the group. 86 00:06:24,020 --> 00:06:29,320 But when the mask is all zeroes, that basically says, don't even consider 87 00:06:29,320 --> 00:06:31,640 the group when creating the hash. 88 00:06:31,640 --> 00:06:35,100 None of the bits in the group matter. 89 00:06:35,100 --> 00:06:44,680 Just hash against the IP address. 90 00:06:44,680 --> 00:06:50,080 And you can now you might say, OK, well, I want to start doing some load 91 00:06:50,080 --> 00:06:53,580 bouncing like you talked about, Keith, I want to have some groups hash 92 00:06:53,580 --> 00:06:57,920 to RP number one, other groups hash to RP number two. 93 00:06:57,920 --> 00:06:59,700 How do I do that? 94 00:06:59,700 --> 00:07:04,820 Well, that's where it gets to be more of an art form than a science, unless 95 00:07:04,820 --> 00:07:08,500 you really like algorithms and math, which I don't. 96 00:07:08,500 --> 00:07:16,900 So in this particular case, I'm going to change the mask. 97 00:07:16,900 --> 00:07:22,420 OK, it was router eight, eight dot two dot eight dot eight. 98 00:07:22,420 --> 00:07:25,180 Now, let me go over to him. 99 00:07:25,180 --> 00:07:32,720 So what I'm going to do is I'm going to change his hash mask length. 100 00:07:32,720 --> 00:07:35,260 And this command right here from a zero. 101 00:07:35,260 --> 00:07:41,060 Something else. I'm going to say of that 32 bit. 102 00:07:41,060 --> 00:07:45,060 Multicast address. 103 00:07:45,060 --> 00:07:53,960 I want you to hash 31 of them, 31 of those bits. 104 00:07:53,960 --> 00:07:57,300 So theoretically, what this should do, because there's only one bit left, 105 00:07:57,300 --> 00:08:00,620 well, that one bit can only be a zero or one, right? 106 00:08:00,620 --> 00:08:05,540 So theoretically, what this should do is evenly divide the load between 107 00:08:05,540 --> 00:08:09,160 the two RPs. And I'm not sure how it's going to do that, but it should 108 00:08:09,160 --> 00:08:12,660 sort of divide it between both RPs now. 109 00:08:12,660 --> 00:08:18,420 Let's find out. Let's go back to router two. 110 00:08:18,420 --> 00:08:21,520 Has he learned of the new hash length? 111 00:08:21,520 --> 00:08:24,860 Yep. So right here, he's learned of the new length. 112 00:08:24,860 --> 00:08:27,040 So now let's just start testing this. 113 00:08:27,040 --> 00:08:34,660 226, 888. OK, it looks like 2424 is going to be the RP for that. 114 00:08:34,660 --> 00:08:43,140 What about 889? Still looks like R4, 881. 115 00:08:43,140 --> 00:08:49,060 Now we come up with some slightly different numbers, but it's still R4, 116 00:08:49,060 --> 00:08:55,060 888.11. At some point, there we go. 117 00:08:55,060 --> 00:09:02,520 OK, so 888.12. Now we've got the second RP, 8383 coming up with the higher 118 00:09:02,520 --> 00:09:06,360 number. So like I said, it's kind of an art form. 119 00:09:06,360 --> 00:09:10,060 You just have to play around on the BSR with different numbers for the 120 00:09:10,060 --> 00:09:11,760 hash mask length. 121 00:09:11,760 --> 00:09:16,840 But I think it's virtually impossible to predict in advance to come up 122 00:09:16,840 --> 00:09:21,340 with a number where you can predict, OK, if I use 31 or if I use 30, this 123 00:09:21,340 --> 00:09:24,400 RP will be used or that RP will be used. 124 00:09:24,400 --> 00:09:27,180 You know, if you go into the formula in the PIM specification, you might 125 00:09:27,180 --> 00:09:28,540 be able to figure that out. 126 00:09:28,540 --> 00:09:32,540 But that's a lot more work than I would care to do. 127 00:09:32,540 --> 00:09:38,600 And so that's how RPs are selected based on these bootstrap messages that 128 00:09:38,600 --> 00:09:40,280 have been received. 129 00:09:40,280 --> 00:09:44,120 So let's just summarize all this and then we'll be done. 130 00:09:44,120 --> 00:09:47,700 So with the PIM bootstrap router, number one, it's an internet standard 131 00:09:47,700 --> 00:09:51,660 developed for PIM version two. 132 00:09:51,660 --> 00:09:57,320 Number two, you still have the concept of candidate RPs and a BSR. 133 00:09:57,320 --> 00:09:59,620 The BSR has to be discovered first. 134 00:09:59,620 --> 00:10:02,220 It's elected. There's only one. 135 00:10:02,220 --> 00:10:05,900 Everybody finds out who the BSR is. 136 00:10:05,900 --> 00:10:10,360 And then the candidate RPs all unicast their messages to him. 137 00:10:10,360 --> 00:10:15,900 Next, that BSR creates what's called a bootstrap message, which has a 138 00:10:15,900 --> 00:10:20,420 full listing of every single RP he's ever heard from and the group and 139 00:10:20,420 --> 00:10:26,000 the priority for that RP that gets dispersed among the entire network. 140 00:10:26,000 --> 00:10:31,980 And lastly, when an individual router actually needs to use an RP because 141 00:10:31,980 --> 00:10:36,420 it needs to register something and needs to send a join, it goes into 142 00:10:36,420 --> 00:10:40,260 that bootstrap message, which is it has stored that in memory, like we 143 00:10:40,260 --> 00:10:44,840 see here. It performs the hash value, the hash function, and then whichever 144 00:10:44,840 --> 00:10:48,880 RP end up with the highest hash, that's the one that's used right now 145 00:10:48,880 --> 00:10:53,800 for this specific need to register something or to send a join. 146 00:10:53,800 --> 00:10:58,620 And that summarizes this concept of the PIM bootstrap router.