WEBVTT 1 00:00.000 --> 00:04.840 All right, let's just do a quick demo of trace routing and exploring some of 2 00:04.840 --> 00:05.560 these options. 3 00:05.560 --> 00:09.360 So I have this very basic lab topology with the sequence of routers. 4 00:09.360 --> 00:12.640 We're going to be able to tell which router is which just based on the last oct 5 00:12.640 --> 00:13.160 et in the 6 00:13.160 --> 00:14.160 IP address. 7 00:14.160 --> 00:17.580 If it's a dot one, it's router one dot three, it's router three and so on and 8 00:17.580 --> 00:18.240 so forth. 9 00:18.240 --> 00:20.600 And what I have here is a couple of things. 10 00:20.600 --> 00:24.360 First of all, we have OSPF running everywhere in here. 11 00:24.360 --> 00:30.730 However, OSPF is not advertising 11 11 11 11, nor is it advertising four dot WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 11 00:24.360 --> 00:30.730 However, OSPF is not advertising 11 11 11 11, nor is it advertising four dot 12 00:30.730 --> 00:31.320 four dot 13 00:31.320 --> 00:32.880 four dot four. 14 00:32.880 --> 00:37.170 What I did do was I made sure that router three knows where four dot four dot 15 00:37.170 --> 00:37.980 four dot four 16 00:37.980 --> 00:40.740 is based on static routing. 17 00:40.740 --> 00:44.770 And so with that in mind, let's do a couple of trace routes and see exactly how 18 00:44.770 --> 00:45.240 this pans 19 00:45.240 --> 00:46.240 out. 20 00:46.240 --> 00:48.160 And again, we'll take a look at some of these options. 21 00:48.160 --> 00:49.880 So first of all, just a basic trace route. 22 00:49.880 --> 00:53.160 If I were to trace out the IP address that router four knows, one dot one dot 23 00:53.160 --> 00:53.600 one dot 24 00:53.600 --> 00:57.700 one, then I can see that it returns a sequence here from router three, router 25 00:57.700 --> 00:58.600 two and router 26 00:58.600 --> 00:59.600 one. 27 00:59.600 --> 01:01.920 It does give me three different probe responses. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 27 00:59.600 --> 01:01.920 It does give me three different probe responses. 28 01:01.920 --> 01:06.200 It's what we're typically used to seeing out of a traditional trace route. 29 01:06.200 --> 01:10.880 Well now I could do the same command, but I can say probe two. 30 01:10.880 --> 01:14.780 And now we see we're only getting a single probe response out of each TTL entry 31 01:14.780 --> 01:15.080 and I 32 01:15.080 --> 01:16.640 can even do probe one. 33 01:16.640 --> 01:18.960 And I just got a single entry out of each one. 34 01:18.960 --> 01:21.680 And I could already tell it went a whole lot faster. 35 01:21.680 --> 01:26.880 Furthermore, if I were to say something like probe one and then TTL, now we see 36 01:26.880 --> 01:27.360 I have 37 01:27.360 --> 01:29.720 to specify the minimum TTL. 38 01:29.720 --> 01:32.600 And then after this I'll specify the maximum. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 38 01:29.720 --> 01:32.600 And then after this I'll specify the maximum. 39 01:32.600 --> 01:38.700 So if I were to say, you know, TTL of one and then a maximum of, let's just say 40 01:38.700 --> 01:39.480 maximum 41 01:39.480 --> 01:40.800 of two. 42 01:40.800 --> 01:41.800 So how far did we get? 43 01:41.800 --> 01:44.470 Well, we started, we got a response out of router three and then we got a 44 01:44.470 --> 01:45.080 response out 45 01:45.080 --> 01:46.960 of router two here. 46 01:46.960 --> 01:51.170 So that's the dot two, but it is not actually getting to the destination 47 01:51.170 --> 01:52.080 because it ran 48 01:52.080 --> 01:56.160 out of TTL, my maximum TTL for this operation was two. 49 01:56.160 --> 02:01.680 So that is the benefit I suppose of setting it lower is if it does get too far WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 49 01:56.160 --> 02:01.680 So that is the benefit I suppose of setting it lower is if it does get too far 50 02:01.680 --> 02:02.400 into the 51 02:02.400 --> 02:05.570 network or we get to the point where we're timing out, then we don't have to 52 02:05.570 --> 02:06.000 wait as 53 02:06.000 --> 02:07.000 long. 54 02:07.000 --> 02:12.870 However, I can also interestingly do this where I say TTL of two as the minimum 55 02:12.870 --> 02:13.000 and 56 02:13.000 --> 02:15.280 the maximum something like 10. 57 02:15.280 --> 02:20.820 And notice we start here with router two and then we hit router one, but we 58 02:20.820 --> 02:21.240 didn't get 59 02:21.240 --> 02:22.920 a response out of router three. 60 02:22.920 --> 02:25.400 We only got a response out of router two. 61 02:25.400 --> 02:30.570 And the reason we got a response out of router two is because the TTL actually WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 61 02:25.400 --> 02:30.570 And the reason we got a response out of router two is because the TTL actually 62 02:30.570 --> 02:31.320 started at 63 02:31.320 --> 02:33.120 two instead of one. 64 02:33.120 --> 02:36.040 So that's kind of a fun thing to explore there. 65 02:36.040 --> 02:40.780 Lastly, if I were to do a trace route to 11 11 11 11, like we said, that's not 66 02:40.780 --> 02:41.800 being advertised 67 02:41.800 --> 02:45.800 into OSPF and therefore router four doesn't know where it is. 68 02:45.800 --> 02:49.830 So I might get into this situation where it's going, you know, star star star 69 02:49.830 --> 02:50.360 here. 70 02:50.360 --> 02:51.360 We're not getting anything. 71 02:51.360 --> 02:52.840 We're not getting anything. 72 02:52.840 --> 02:55.240 And I have to wait 30 hops for this. 73 02:55.240 --> 02:59.760 Well, I can hit control shift six and there we go. 74 02:59.760 --> 03:00.760 It just broke out of it. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 74 02:59.760 --> 03:00.760 It just broke out of it. 75 03:00.760 --> 03:02.640 So that's a very useful tool. 76 03:02.640 --> 03:04.240 I can also do that if I'm pinging. 77 03:04.240 --> 03:10.480 If I make a mistake and I'm like, Hey, let's do a ping 11 11 11 11. 78 03:10.480 --> 03:12.280 And maybe I even repeated a hundred times. 79 03:12.280 --> 03:14.920 I'm like, Oh man, I've got to sit here for a long time. 80 03:14.920 --> 03:18.440 Yeah, control shift six works out pretty well. 81 03:18.440 --> 03:19.440 Okay. 82 03:19.440 --> 03:21.760 And lastly, the source concept. 83 03:21.760 --> 03:27.880 So let's say I wanted to do my trace route sourcing from this four dot four dot 84 03:27.880 --> 03:28.320 four 85 03:28.320 --> 03:29.320 address. 86 03:29.320 --> 03:32.580 We know router three knows where it is, but we do but router two and router one WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 86 03:29.320 --> 03:32.580 We know router three knows where it is, but we do but router two and router one 87 03:32.580 --> 03:33.000 have no 88 03:33.000 --> 03:34.360 awareness. 89 03:34.360 --> 03:39.760 So let's do our trace route and we'll specify an IP address we can get to. 90 03:39.760 --> 03:44.440 And then I'm going to also specify my source of four dot four dot four. 91 03:44.440 --> 03:47.160 And we'll just go ahead and do a probe of one. 92 03:47.160 --> 03:50.330 So what we get is we get a response from router three because router three 93 03:50.330 --> 03:51.120 knows how to get 94 03:51.120 --> 03:56.540 back to four, four, four, four router four is sending this trace route with a 95 03:56.540 --> 03:57.480 source IP 96 03:57.480 --> 04:01.190 address of four, four, four, four, and therefore the response from these WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 96 03:57.480 --> 04:01.190 address of four, four, four, four, and therefore the response from these 97 04:01.190 --> 04:02.220 devices is going to 98 04:02.220 --> 04:04.360 be directed to four, four, four, four. 99 04:04.360 --> 04:05.760 They just don't know where it is. 100 04:05.760 --> 04:09.710 At least routers one and router and routers one and two do not know how to get 101 04:09.710 --> 04:10.240 back. 102 04:10.240 --> 04:14.080 And so we got a response out of router three, but not out of routers two and 103 04:14.080 --> 04:14.560 one. 104 04:14.560 --> 04:18.040 And this is going to go until the max of 30, which is why we'd want to break 105 04:18.040 --> 04:18.440 out. 106 04:18.440 --> 04:22.400 So this is just a fun way to explore trace route options. 107 04:22.400 --> 04:27.010 Again, it's so easy just to use a command like this that we use a lot and just 108 04:27.010 --> 04:27.520 always 109 04:27.520 --> 04:30.040 use the basic options. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000 109 04:27.520 --> 04:30.040 use the basic options. 110 04:30.040 --> 04:35.120 Well, use these options to our advantage and using especially the source option 111 04:35.120 --> 04:35.360 to be 112 04:35.360 --> 04:39.910 able to make sure certain subnets are reachable is very powerful and making it 113 04:39.910 --> 04:40.760 so that we're 114 04:40.760 --> 04:44.810 more efficient with the probe and numeric, which we didn't demonstrate here, 115 04:44.810 --> 04:45.360 but we can 116 04:45.360 --> 04:49.080 use that to avoid the DNS lookups that might take us a long time.