ccna 200-301 network simulator ns21 tv

ccna 200-301 network simulator ns21 tv.Frame Header Network Layer Header Transport Layer Header Datapipe Tail Destination Source Destination IP Source IP Destination Port Source Port|oo-11-BC-7D-25-03100-1B-24-7D-25-01 |195.1.1.2 | 193.1.1.2 | 23 | i 1030 1 Telnet data] CRC check|Figure 2.6-3 Format of the data frame sent by PC1The encapsulated data frames from the data link layer are passed to the physical layer and converted into a stream of bits (Bit) in binary form to be sent out from PC1's NIC. The purpose of the physical layer is to process the bit stream and convert the bits into electronic, optical or microwave signals. Conversely at the receiving end, the physical layer reacquires these signals from the transmission media, recovers them into a bit stream, and transmits the bit stream to the data link layer.Step 2: The bitstream from PC1 arrives at the hub (note that the icon in Figure 2-6-1 indicates a hub), which simply amplifies the bitstream and forwards it outbound from all ports except the receive port. PC2 receives this packet, converts the bitstream into frames for upload to the data chain45 APC2 compares the destination MAC address of the data frame and finds that it is different from the MAC address of the local NIC, PC2 discards the data frame and gives up processing.Step 3: Router R1 receives the bitstream and converts it into a frame for upload to the data link layer. Router R1 compares the destination MAC address of the data frame and finds that it is the same as the MAC address of the router's receive port FaO/O (FastEthemet,Fast Ethernet, abbreviated as FaO/O, referring to the interface numbered 0 on slot 0), and the router knows that the data frame is sent to this router. Router R1's data link layer decapsulates the frame and uploads it to Router R1's network layer. Router R1 sees that the destination IP address of the packet is 195.1.1.2, which is not addressed to this router and needs to be forwarded by the router.Router R1 queries its own routing table and finds that the packet should be sent from serial interface S1/1. Router R1 exchanges the packet from the FaO/O interface to the S1/1 interface.At this point R1 is not able to send this packet out directly because it was decapsulated at R1's FaO/O interface and now needs to be re-encapsulated. Imagine a windy and snowy day where you take off your hat on the way in and need to put it on again on the way out. The same is true for data encapsulation, where the incoming interface at the router is unencapsulated and the outgoing interface at the router needs to be re-encapsulated. The difference with a person taking off their hat is that what is removed by the unencapsulation here is not the same as what is added by the re-encapsulation. The network layer is not unencapsulated, but that does not mean that the information at the network layer is not changed at all. In fact, the source and destination IP addresses of the packets at the network layer are not changed (except in the case of network address translation), but the TTL (the survival period, which was described earlier) is reduced by "The network layer hands the packet to the lower data link layer, which needs to encapsulate the address of the second layer. The serial link is different from Ethernet because Ethernet is a multi-access network and the MAC address is needed to locate the destination device. (High-Level DataLinkControl) encapsulation, which is used for point-to-point lines, that is, a cable that connects only two devices, with one end sending and the other end definitely receiving. Assuming that the PPP protocol is used on the serial cable, the data frame format of the data link layer encapsulated with both source and destination addresses from PPPo router R1 is shown in Figure 2-6-4.