1 00:00:19,600 --> 00:00:23,720 Okay, so let's see if we can practically answer these questions. 2 00:00:23,950 --> 00:00:31,420 To do that I'm gonna use simulation mode in packet tracer and I'm gonna change the filters to 3 00:00:31,480 --> 00:00:36,160 only show ARP and ICMP messages. 4 00:00:36,160 --> 00:00:44,170 I don't wanna see all the other traffic types in the network. So let's see what happens when PC 1 pings 5 00:00:44,170 --> 00:01:02,420 PC 4. PC 1 has an IP address of 10 111, PC 4 has an IP address of 10 114 so we're going 6 00:01:02,420 --> 00:01:04,700 to send ICMP traffic 7 00:01:04,700 --> 00:01:05,960 in other words ping traffic 8 00:01:08,670 --> 00:01:16,150 from PC 1 to PC 4 and then we're going to observe what happens. Now in this example 9 00:01:16,150 --> 00:01:18,890 I'll only send two packets. 10 00:01:19,030 --> 00:01:28,410 In other words two pings, notice what happens in the network there's ICMP traffic but there is also an 11 00:01:28,440 --> 00:01:31,520 ARP frame that's generated. 12 00:01:31,650 --> 00:01:37,110 PC 1 needs to learn the MAC address of PC 4 13 00:01:37,320 --> 00:01:47,820 so it sends out an ARP which is a broadcast requesting the target MAC address of PC 4. So in answer 14 00:01:47,820 --> 00:01:51,320 to our first question, what type of packet is sent 15 00:01:51,330 --> 00:01:58,250 initially? The answer is a ARP packet which is a broadcast packet. 16 00:02:02,170 --> 00:02:08,280 We've proven that by running simulation mode in Packet Tracer. 17 00:02:08,289 --> 00:02:16,510 Now this is a broadcast and in this network, the devices are connected to a hub so the traffic should 18 00:02:16,510 --> 00:02:25,670 be flooded to all devices in the network except the device that sent the packet. 19 00:02:25,670 --> 00:02:27,500 So who receives the packet? 20 00:02:27,530 --> 00:02:28,510 PC 2 does, 21 00:02:28,520 --> 00:02:41,380 PC 3 does and so does PC 4, PC 2 and PC 3 will drop the packets because the ARP packet is not for 22 00:02:41,530 --> 00:02:52,830 their IP address, PC 2 as an example is configured with IP address 10 112 so PC 2 is gonna drop the 23 00:02:52,830 --> 00:02:53,660 packet. 24 00:02:53,910 --> 00:03:04,010 The ARP request is for IP address 10 114 so both PC 2 and PC 3 25 00:03:04,020 --> 00:03:14,360 drop the packet but PC 4 will accept the packet and what it should do now is send back an ARP reply. 26 00:03:14,750 --> 00:03:27,400 So if we look at this packet notice the inbound packet to the hub is an ARP reply packet with the MAC 27 00:03:27,400 --> 00:03:32,020 address of PC 4 this is PC 4s IP address 28 00:03:32,050 --> 00:03:34,090 this is its MAC address. 29 00:03:34,090 --> 00:03:46,170 We can verify that by using the IP config command and I should say IP config slash all notice the MAC 30 00:03:46,170 --> 00:03:55,650 address which is the source MAC address of the frame and that's the source MAC address we see over here. 31 00:03:55,650 --> 00:04:00,120 So the next question is, who receives the return traffic? 32 00:04:00,120 --> 00:04:11,180 So if I click capture forward notice PC 1, PC 3 and PC 2 receive the return traffic so it PC 33 00:04:11,180 --> 00:04:13,300 1, PC 2 and PC 3. 34 00:04:13,490 --> 00:04:23,740 PC 2 and PC 3 will drop the ARP reply because it's not destined to them when we look at that packet 35 00:04:24,580 --> 00:04:33,320 we can see that the destination MAC address is PC1 and we can confirm that by looking at the config 36 00:04:33,320 --> 00:04:44,420 of PC1 notice the MAC address is this, so PC2 and PC 3 will drop the ARP 37 00:04:44,410 --> 00:04:53,840 reply. We're then asked when ping traffic is sent from PC 1 to PC 4 who receives the traffic. 38 00:04:53,840 --> 00:04:58,280 Now it's a hub so the traffic will be flooded. 39 00:04:58,440 --> 00:05:10,320 So here's the ICMP message we can see that it's an Ethernet 2 frame using IP 4 at layer 3 and 40 00:05:10,320 --> 00:05:16,440 we can see it's an ICMP packet and when we click capture forward notice 41 00:05:16,550 --> 00:05:29,850 PC 2, PC 3 and PC 4 receive the traffic but again PC 2 and PC 3 will drop the packet because 42 00:05:29,850 --> 00:05:40,670 it's not destined to them when we look at the inbound PDU or protocol data unit on PC 4 we can 43 00:05:40,670 --> 00:05:47,880 see that the destination IP address is PC 4 and the destination MAC address is 44 00:05:47,880 --> 00:05:58,270 PC 4 we can verify that once again by using the IP config slash all command and we can see the MAC 45 00:05:58,270 --> 00:05:59,170 address of 46 00:05:59,170 --> 00:06:02,950 PC 4. So that's going to continue now 47 00:06:03,410 --> 00:06:03,980 When the 48 00:06:03,980 --> 00:06:08,320 PC 4 replies to PC 1 49 00:06:08,400 --> 00:06:15,660 the traffic is flooded and this is the problem with the hub even though the conversation is between 50 00:06:16,110 --> 00:06:23,480 PC 1 and PC 4 everyone in the network receives the traffic.