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These are the user uploaded subtitles that are being translated: 1 1 00:00:00,000 --> 00:00:06,000 On the DHCP server, we could use commands such as, show ip dhcp binding 2 2 00:00:07,000 --> 00:00:12,000 to see the client ID that's associated with an IP address. 3 3 00:00:13,000 --> 00:00:14,000 So this IP address is being allocated 4 4 00:00:15,000 --> 00:00:18,000 to this client ID here and it was allocated automatically. 5 5 00:00:19,000 --> 00:00:21,000 Now that client ID isn’t very easy to read. 6 6 00:00:22,000 --> 00:00:28,000 So what I’ll do is go into the interface on the client 7 7 00:00:29,000 --> 00:00:33,000 and shut that down, in this example a DHCP release message was sent 8 8 00:00:34,000 --> 00:00:37,000 to the DHCP server before the interface was shut down. 9 9 00:00:38,000 --> 00:00:44,000 So when we look at the binding on the DHCP server, no binding now exist. 10 10 00:00:45,000 --> 00:00:54,000 So ip dhcp client and we'll specify a client-id in ascii 11 11 00:00:55,000 --> 00:01:03,000 and you'll simply set it to PC 2 and hit enter 12 12 00:01:04,000 --> 00:01:07,000 and then use the command no shut to bring the interface up. 13 13 00:01:08,000 --> 00:01:16,000 So we see a discover message, there’s an offer request from the client 14 14 00:01:17,000 --> 00:01:19,000 and an acknowledgement from the server. 15 15 00:01:20,000 --> 00:01:27,000 show dhcp lease what we can see here is the client ID is set to PC 2 16 16 00:01:28,000 --> 00:01:30,000 and this is the client ID hexadecimal dump. 17 17 00:01:31,000 --> 00:01:41,000 On the server show ip dhcp binding notice the user name is the same as on the client. 18 18 00:01:42,000 --> 00:01:48,000 This can be converted from hexadecimal to ASCII and you’ll get PC 2. 19 19 00:01:49,000 --> 00:01:54,000 As an example, the hexadecimal value 50 is the decimal value 80 20 20 00:01:55,000 --> 00:01:56,000 and equates to capital P 21 21 00:01:57,000 --> 00:02:04,000 in the same way hexadecimal 43 is capital C and hexadecimal 32 is value 2. 22 22 00:02:05,000 --> 00:02:09,000 So this equates to PC 2 which can also be seen on the server. 23 23 00:02:10,000 --> 00:02:14,000 So I wanted to shut that interface down, and show you Wireshark. 24 24 00:02:15,000 --> 00:02:19,000 So I'll shut it down, I’ll start a Wireshark capture. 25 25 00:02:20,000 --> 00:02:26,000 On the server router 2 and on router 1 26 26 00:02:27,000 --> 00:02:32,000 I'll no shut the interface and let’s see if we get some DHCP messages. 27 27 00:02:33,000 --> 00:02:36,000 So firstly, here's a DHCP discover message. 28 28 00:02:37,000 --> 00:02:42,000 Bootstrap protocol discover, so DHCP discover 29 29 00:02:43,000 --> 00:02:49,000 source port is UDP port 68, destination port is UDP port 67 30 30 00:02:50,000 --> 00:02:53,000 it’s a boot request or DHCP request 31 31 00:02:54,000 --> 00:03:00,000 notice the client MAC address is A,B,C as configured, the client IP address is 0. 32 32 00:03:01,000 --> 00:03:04,000 The PC doesn’t know what IP address to use 33 33 00:03:05,000 --> 00:03:09,000 and it doesn’t know about any DHCP servers. so it sending a message 33 34 00:03:10,000 --> 00:03:15,000 to the broadcast address 255.255.255.255 so you can see it’s a discover. 34 35 00:03:16,000 --> 00:03:18,000 There's other information here including the host name 35 36 00:03:19,000 --> 00:03:23,000 of the device making the request, as well as a client identifier. 36 37 00:03:24,000 --> 00:03:30,000 Scrolling down a bit further, we can see the offer from the DHCP server. 37 38 00:03:31,000 --> 00:03:34,000 So this is from the server to a broadcast address 38 39 00:03:35,000 --> 00:03:38,000 because the client doesn’t have an IP address, it needs to be a broadcast. 39 40 00:03:39,000 --> 00:03:45,000 So it's a DHCP offer, offering this IP address to a client with this MAC address. 40 41 00:03:46,000 --> 00:03:50,000 We can see information such as, once again it’s an offer 41 42 00:03:51,000 --> 00:03:53,000 client identifier, so that's the server IP address 42 43 00:03:54,000 --> 00:03:58,000 lease time is 7 days because we configure that manually. 43 44 00:03:59,000 --> 00:04:04,000 We can see the subnet mask being /24, we can see option 3 44 45 00:04:05,000 --> 00:04:09,000 default gateway, we can see option 6, DNS server 45 46 00:04:10,000 --> 00:04:13,000 and we can see option 150 TFTP server. 46 47 00:04:14,000 --> 00:04:17,000 The client then request that address 47 48 00:04:18,000 --> 00:04:20,000 the clients still doesn’t have an IP address 48 49 00:04:21,000 --> 00:04:27,000 so it sends it from a source IP address of 0.0.0.0 to a broadcast 49 50 00:04:28,000 --> 00:04:34,000 and it's asking the server through the request 50 51 00:04:35,000 --> 00:04:43,000 if it can have this IP address that was previously offered 10.1.1.14 51 52 00:04:44,000 --> 00:04:48,000 the server then acknowledges, that the client can have that address 51 53 00:04:49,000 --> 00:04:50,000 notice it's still a broadcast 52 54 00:04:51,000 --> 00:04:56,000 so the server is telling the client that, yes they can use this IP address. 53 55 00:04:57,000 --> 00:04:59,000 so the client, with this Mac address once again 54 56 00:05:00,000 --> 00:05:05,000 has now being drawn to the right to use that IP address 10.1.1.14 55 57 00:05:06,000 --> 00:05:09,000 so the client can now start using this address 56 58 00:05:10,000 --> 00:05:15,000 and we can see that on the client, that it was assigned this IP address. 6048