ccna textbook pdf

ccna textbook pdf.fails, there is a physical layer problem: the switch port connected to the current host may not be enabled; the cable is not connected properly; orthe cable is damaged. Next, ping the default gateway address to verify that connectivity to the current subnet exit is okay. Finally, use thetraceroute (Windows command tracert) to see where on the Layer 3 network the problem lies.2. PC.A sends TCP SYN to PC.BOnce PC-A knows PC-B's IP address, the Telnet application can proceed to Telnet, which uses TCP at the transport layer and therefore must first perform three handshakes. The first step is for PC-A to send a TCP data segment with the SYN bit (often referred to as a flag) set. The source port it uses is a dynamic port greater than 49151, and the destination port is the well-known port used for Telnet 23o PDU1 in Table 9.2 illustrates the Ethernet frame header, IP packet header, and TCP header information for this frame. Note that the next-hop Layer 2 address is the Router A-aware gateway.The router receives this frame and processes the header information, and at layer 3 it finds that the destination IP address is not its own IP address, so the router looks up the routing table and finds that the next hop at layer 3 is router B. Table 9.2 TCP SYN sent to PC-BExam Essentials If the link between Router A and Router B fails, Router A sends PC-A an ICMP destination unreachable message with a source address of10.0.1.2 ICMP destination unreachable message. If the link between Router B and PC.B goes down, Router B will send an ICMP Destination Unreachable message to PC-A with a source address of 10.0.2.2. This at least allows you to know what the problem is. If you are using a ping application that does not show "destination unreachable" but only "answer timeout", you can use traceroute (Windows command tracert) to find out more about what the problem is.If Router A does not know the IP address to MAC address mapping for Router B, it will use ARP to find out. Router A then re-encapsulates the IP packet into a new Ethernet frame, as shown in PDU 2 of Table 9.2:The IP header and TCP header remain the same, but a new frame header is generated to transmit the information over subnet 10.0.2.0/24.Upon receiving this frame, Router B notices that the destination IP address is not its own IP address, so Router B looks at the routing table to determine where the packet should be forwarded. Here, Router B is directly connected to the destination subnet 10.0.3.0/24. If Router B does not know the IP address to MAC address mapping for PC-B, it will use ARP to learn about it. During the ARP request process, Switch B will learn the MAC address of Router B and add that address and Port 1 to the CAM table (if Switch B has not already done so). Similarly, during the ARP answer, Switch B will learn the MAC address of PC-B (if it has not already done so). Next, Router B encapsulates the 1P packet into a new frame in order to transmit this data to PC-B O The frame header, IP packet header, and TCP data segment header of this Ethernet frame are shown in Table 9.2 for UDP3.