1 00:00:09,660 --> 00:00:16,940 This is one of multiple videos discussing Dynamic Host Configuration Protocol or DHC. 2 00:00:17,250 --> 00:00:19,900 This is a DHP trouble shooting video. 3 00:00:20,370 --> 00:00:28,500 We've been told that the client on the left in the apology is not receiving IP addresses from the DHP 4 00:00:28,500 --> 00:00:30,380 server on the right. 5 00:00:30,390 --> 00:00:32,810 So let's investigate what's happening. 6 00:00:33,240 --> 00:00:42,540 So here's the client I'm using an Iowas Virata to mimic a client in this Janissary typology show IP 7 00:00:42,540 --> 00:00:44,270 interface brief. 8 00:00:44,430 --> 00:00:53,270 We have a gigabit 00 configured for DHP but the interface is currently administratively down. 9 00:00:53,310 --> 00:01:01,860 So lets enable that interface show IP interface brief interfaces. 10 00:01:01,860 --> 00:01:12,220 Now up up as we can see here but at the moment we are not receiving an IP address from the DHP server. 11 00:01:13,400 --> 00:01:23,570 This road is acting as the DHP server so show IP DHP pool allows us to see that a DGP pool is configured 12 00:01:23,600 --> 00:01:32,840 on this Rodda with the name PC pool there are 254 addresses configured in the pool in this range. 13 00:01:33,140 --> 00:01:38,410 No addresses have been least at the moment show IP DHP binding. 14 00:01:38,520 --> 00:01:48,550 So shows us that no addresses have been least to any devices so D-bag IP DHP server packet. 15 00:01:48,800 --> 00:01:51,200 Let's have a look in real time what's happening. 16 00:01:51,440 --> 00:01:55,160 The client still doesn't have an address. 17 00:01:55,250 --> 00:02:04,820 So what I'll do is shut the interface down and then no shut it to see if that makes any difference. 18 00:02:04,830 --> 00:02:06,720 So the interface comes up. 19 00:02:06,720 --> 00:02:10,100 But notice we see no output on the DHP server. 20 00:02:10,900 --> 00:02:13,390 In addition to using CLIA commands. 21 00:02:13,390 --> 00:02:20,080 What I'm going to do here is use white shark and capture traffic on the link between the client and 22 00:02:20,080 --> 00:02:23,630 the router to see if DHP requests are being sent. 23 00:02:24,590 --> 00:02:33,380 So notice we do see a DHP discover it's coming from a device with no IP address and it's going to broadcast 24 00:02:33,380 --> 00:02:45,180 of 4:35 five to four five the source port is UDP or use a datagram protocol port 68 destination 67. 25 00:02:45,200 --> 00:02:48,340 This is the bootstrap protocol. 26 00:02:48,370 --> 00:02:51,180 In other words it's a DHP discover message. 27 00:02:51,310 --> 00:02:56,700 The client is trying to discover a DHP server on the network. 28 00:02:56,950 --> 00:03:07,400 In additional Stata y shot capture on the site to see if any DHP messages are received on the server 29 00:03:07,400 --> 00:03:10,420 side set back on the client. 30 00:03:10,420 --> 00:03:12,170 I'll shut the interface down 31 00:03:15,120 --> 00:03:17,590 oh no shut it. 32 00:03:17,790 --> 00:03:24,320 And let's see if we see any DHP traffic on the server side server side is seeing no traffic at all. 33 00:03:26,920 --> 00:03:35,080 But the client site is seeing DHP discover messages and there are quite a few of them. 34 00:03:35,940 --> 00:03:41,730 Now and why is shocked if you full to full DGP it doesn't work. 35 00:03:41,860 --> 00:03:43,830 So you need to full to boot. 36 00:03:44,350 --> 00:03:52,720 So use Boot P rather than DHP when filtering for messages we see a lot of DHP discover messages on the 37 00:03:52,720 --> 00:03:56,800 client side but none on the server side. 38 00:03:58,590 --> 00:04:05,820 So it looks like the DHP discover message is hitting the router but is not being sent to the server. 39 00:04:05,850 --> 00:04:08,750 Now notice the type of message used. 40 00:04:08,790 --> 00:04:17,680 This is a broadcast a broadcast is not forwarded by a broader or lazy switch. 41 00:04:17,680 --> 00:04:24,000 Something needs to be configured on the router to able that traffic to be sent to the server. 42 00:04:25,100 --> 00:04:30,110 So show run interface gigabit 00 can you find the problem. 43 00:04:30,110 --> 00:04:32,370 I've given you a few hints. 44 00:04:32,570 --> 00:04:40,420 Once again DHP messages are being received by the router but they not being sent to the DHP server. 45 00:04:41,850 --> 00:04:52,000 What's missing in this configuration OK so DGP messages are dropped by the router because they broadcast 46 00:04:52,000 --> 00:05:01,310 messages unless you enable the IP help address command so we need to enable the IP help address and 47 00:05:01,310 --> 00:05:04,440 then send the traffic to the DHP server. 48 00:05:05,610 --> 00:05:11,390 Now this typology the DHB server has the same IP address. 49 00:05:11,850 --> 00:05:19,860 So we need to configure the IP help address on Rodda too and pointed to the DHP server. 50 00:05:19,860 --> 00:05:26,790 Now that I've done that let's see if DHP messages are forwarded to the server. 51 00:05:27,130 --> 00:05:37,010 And notice without doing anything else we can now see the DHP discover this is between the Rodda and 52 00:05:37,010 --> 00:05:39,780 the server full to boot. 53 00:05:39,860 --> 00:05:53,420 Notice there's the Discover message from 10 1 1 2 5 4 to 10 1 to 1 not 2 5 4 is Rodda to 54 00:05:56,450 --> 00:06:08,020 notice the Discover message was forwarded to the DHP server for a client with the name client. 55 00:06:08,020 --> 00:06:14,500 In other words Rato one acting as the client. 56 00:06:14,730 --> 00:06:21,120 You can see in the output here that the broader received an IP address from the DHP server and you can 57 00:06:21,120 --> 00:06:22,560 see that here as well. 58 00:06:25,210 --> 00:06:34,590 So this is the DHP discover forwarded to the server the servers then replying back to the Rodda with 59 00:06:34,590 --> 00:06:45,070 the not for saying that this is the service IP address list time is one day default gateway or default 60 00:06:45,070 --> 00:06:47,660 grottos 10 1 1 2 5 4. 61 00:06:47,950 --> 00:06:50,720 The client is requesting the address. 62 00:06:50,740 --> 00:06:55,170 So is why Shaw captures on the right hand side of this typology. 63 00:06:55,360 --> 00:07:00,100 So the client would have sent that message to the router and the router is now forwarding that message 64 00:07:00,130 --> 00:07:04,440 to the server. 65 00:07:04,460 --> 00:07:08,130 We can see that by looking at the Y shall capture here. 66 00:07:08,390 --> 00:07:11,420 Here's the offer from the server to the client. 67 00:07:12,280 --> 00:07:18,520 And he has the client sending a broadcast requesting the address brought costs and not forwarded by 68 00:07:18,640 --> 00:07:25,530 the broader the client is requesting the address from the DHP server. 69 00:07:25,760 --> 00:07:31,670 The DGP survey acknowledges that and gives the client the address 10 1 1 2. 70 00:07:32,020 --> 00:07:40,820 So previously the address that was offered to the client was 10 1 1 2 and that was given to the relay 71 00:07:40,820 --> 00:07:44,570 agent 10 1 1 2 5 4 in other words the broader 72 00:07:49,250 --> 00:07:54,670 the client is requesting that address and the DHP of acknowledges that. 73 00:07:54,680 --> 00:07:56,300 So hence the client will rot. 74 00:07:56,320 --> 00:08:05,000 One is given this IP address and if we look at the writing table it's been allocated 10 1 1 2 5 4 as 75 00:08:05,000 --> 00:08:12,410 its default gateway and that's because on the DHB server and notice we can see all the debugs showing 76 00:08:12,410 --> 00:08:17,870 you DHB discover DHP request and so forth. 77 00:08:19,960 --> 00:08:22,270 DHP server has been configured 78 00:08:26,360 --> 00:08:31,410 with this configuration client is being allocated an address in this range. 79 00:08:31,650 --> 00:08:41,450 Default Rodda is 10 1 1 2 4 4 DNS server is 10 1 to 1 which is the DHP server. 80 00:08:41,450 --> 00:08:47,740 So that was an example of how to troubleshoot Dynamic Host Configuration Protocol or DHV. 81 00:08:48,010 --> 00:08:49,640 I hope you enjoyed the video. 82 00:08:49,850 --> 00:08:54,370 If you did please like it please subscribe to my YouTube channel. 83 00:08:54,380 --> 00:08:56,020 I wish you all the very best.