ccna refresher pdf

ccna refresher pdf.Figure 5.3 Example of ARP involving a routerStep 1: PC-A sends an ARP request for the default gateway MAC address Step 4: The router sends an ARP request for the MAC address of PC-BAfter the router receives the Ethernet frame, it compares its destination MAC address with the MAC address of its own Ethernet interface and finds that they are identical. Therefore, the router unwraps the Ethernet frame and makes a routing decision based on the destination IP address 2.2.2.2. Here, the destination network is directly connected to the router's second interface and is also Ethernet. In step 4, if the router does not have the MAC address of PC.B in its ARP table, it sends an ARP request for the MAC address of PC.B (222.2). In step 5, the router receives an answer. In step 6, the router encapsulates the original IP packet into a new Ethernet frame with its source MAC address set to the MAC address of the second interface and its destination MAC address set to the MAC address of PC-B. o When PC-B receives this frame, it knows that it was sent to itself (because its destination MAC address matches its own MAC address) and that the encapsulated IP packet is from PC-A (this is known from the source IP address in the Layer 3 IP header)Notice that in this example, the IP address in the packet is not modified by the router, but two Ethernet frames are used in order to transmit the IP packet to its destination. Also, each device stores the MAC address in its own ARP table so that when PC-A needs to send information to PC-B later, these devices do not have to send ARP requests.ARP is used to learn the Layer 2 addresses of other devices in the current broadcast domain so that you can communicate with those devices. Be sure to familiarize yourself with how devicesWhether the communication between devices takes place at Layer 2 or Layer 3. When there is a router between the source and the target device, the source device uses its MAC address at Layer 2 as the source address.The source device uses its MAC address as the source address and the MAC address of the default gateway as the destination address at Layer 2. Note that the IP address is used forLayer 3 communication, and routers do not modify them.ARP assumes that the device whose MAC address is to be requested via ARP is located in the current network segment. For example, in Figure 5.4, PC.A assumes that it is located in the current broadcast domain based on the router's IP address 1.1.1.2, and this assumption is correct. If PC.A generatesgenerates an ARP request broadcast asking for the router's MAC address, the router will see the request. However, you may encounter a situation where you move a device from one part of the network to another, but must retain its IP address.