Computer Network-Cisco Packet Tracer Experiment

---

Preface

There are 15 experiments in this part, which need to be completed using Cisco Packet Tracer software.
Please understand the concepts of VLSM, CIDR, RIP, OSPF, VLAN, STP, NAT, and DHCP first to be able to plan and configure the network.

Reference:
Packet Tracer's simple use of
Cisco Packet Tracer experimental tutorial

Introduction
to the use of CPT software Please use the reference link 1 above to understand and familiarize yourself with the use of CPT software.

---

Specific experiment

1. Directly connect two PCs to construct a LAN

Connect two PCs directly to form a network. Note: A crossover cable is required for direct connection.
For the basic network configuration of two PCs, you only need to configure the IP address, and then ping each other to succeed.

2. Build a LAN with a switch

Some screenshots:

Question
1. Can PC0 ping PC1, PC2, PC3?
2. Can PC3 ping PC0, PC1, PC2? why?
3. Change the masks of the 4 PCs to 255.255.0.0, can they ping each other? why?
4. Do I need to configure a gateway for the network connected with the Layer 2 switch? why?
1. PC0 can ping PC1 but cannot ping PC2, PC3.
2. PC3 can only ping PC2, but cannot ping PC0, PC1. Because PC3 and PC2 are in the same subnet, not in the same subnet as PC0 and PC1
. 3. After changing the masks of all 4 PCs to 255.255.0.0, they can be pinged because their IP addresses are the same as the subnet masks. And the result obtained is 192.168.0.0, under the same subnet.
4. No gateway is required.
(Switch interface address list
Layer 2 switch is a plug-and-play multi-interface device, it has three processing methods for received frames: broadcast, forward and discard (please figure out when and what operation). Then If the forwarding is successful, the switch must have an interface address list, namely the MAC table, which is automatically obtained by the switch through learning!
Still construct the topological structure of the above figure, and configure the IP of each computer in the same subnet, use Click on the magnifying glass in the toolbar, such as Switch3 on the left, and select MAC Table, you can see that the MAC table of the switch is empty at first, that is, it does not know how to forward frames (then how will it be processed?), use PC0 to access After (ping) PC1, check the MAC table of the switch. Now there are corresponding records. Please think about how to get it. With the increase of network communication, each switch will generate its own complete MAC table. At this time, the switching speed of the switch Is the fastest!)

3. Spanning Tree Protocol (Spanning Tree Protocol)

The switch needs to broadcast when the destination address is unknown or when the broadcast frame is received. If there are loops/loops between switches, broadcast loop storms will occur, which will seriously affect network performance.
The STP protocol running in the switch can avoid broadcast loop storms between switches.
Using only switches, construct the following topology:

This is the initial state. We can see that there is a loop between the switches, which will cause broadcast frames to be transmitted cyclically, that is, a broadcast storm, which seriously affects network performance.

Subsequently, the switch will automatically block the redundant lines through the Spanning Tree Protocol (STP) to form a tree with a unique path, namely the spanning tree, with Switch4 as the root (specifically which root switch has a related strategy) !

After a period of time, following the successful construction of the spanning tree with the STP protocol, the two interfaces of Switch5 are currently physically connected, but logically unconnected, they are in the Blocking state (orange) as shown in the figure below:

My description here is different from the original description, there is a little difference

During network operation, if there is a problem with the physical connection between Switch4 and Switch5 (cut off the connection between Switch4 and Switch5), the spanning tree will automatically change. The previously Blocking interface above Switch5 is now active (green), but the lower interface is still in the Blocking state (orange). As shown below:

There will be an error when I run here, the reason is unknown

Note: The STP protocol of the switch, that is, the Spanning Tree Protocol, always automatically guarantees that there will be no loops between the switches, thus forming a broadcast storm.

4. Preliminary router configuration

We simulate the connection between Chongqing Jiaotong University and Chongqing University and construct the following topology:

Explain 1:
Jiaotong University and Chongqing University are obviously two different subnets. The communication between different subnets needs to pass through the router.
Each interface of the router has at least one subnet. In the figure, we simply planned 3 subnets:

1. The router on the left is from Jiaotong University. A switch is used to connect to the network of Jiaotong University. The network number is 192.168.1.0/24. The router interface is also the gateway of the Jiaotong University network. The assigned IP is 192.168.1.1
2. The router on the right is Chongqing For universities, use a switch to connect to the network of Chongqing University, and assign the network number 192.168.3.0/24. The router interface is also the gateway of the Chongqing University network, and the assigned IP is 192.168.3.1
3. The two routers are connected by a wide area network interface. It is also a subnet, and the network number 192.168.2.0/24 is assigned

Note 2 In
reality, the connection between Jiaotong University and Chongqing University is remote. The connection is made either through the optical fiber interface of the router, or through the WAN interface, the so-called serial port (as shown in the topology diagram), generally not through a twisted pair connection (why?).
Below we take the connection through the WAN port of the router as an example to carry out the relevant configuration. Please note: The router we chose does not have a WAN module (named WIC-1T, etc.) by default. You need to turn off the router and add it, and then turn it on again.

Note 3:
Attention should be paid to the DCE and DTE ends in the analog WAN connection (there is a prompt on the line when connecting, and the one with a clock mark is the DCE end. For the concepts of DCE and DTE, please refer to the relevant information.), the DCE end needs to be configured Clock frequency 64000

Note 4 The
router has multiple command line configuration modes, each of which corresponds to a different prompt and corresponding authority.
Please pay attention to input configuration-related commands in the correct mode.

User mode: User mode
Privileged mode: Privileged mode
Global configuration mode: Global configuration mode
Interface mode: Interface configuration mode
Subinterface mode: Subinterface configuration mode

Note 5
In reality, it is obvious that the new router cannot be configured remotely. We must connect to the console interface of the router through the serial port of the notebook and perform the initial configuration (note that the bit rate is set to 9600) before remotely through the network. Configure it. This is also the purpose of the notebook connection drawn on the upper left of the picture above.

Note 6
In the CLI interface of the router, you can see that just after the router is successfully started, because there is no configuration, you will be prompted whether to enter the initial configuration dialog (Would you like to enter the initial configuration dialog?). Because of the many steps, please select The
configuration data of each interface of the router in the NO topology is as follows: The configuration data

of each PC in the topology is as follows:

Problem
: Now the PCs and gateways in Jiaotong University can ping each other, and Chongqing University is similar. But it is not possible to ping major PCs from the PC of National Chiao Tung University, and vice versa, that is, it cannot cross subnets. why?
Broadcast messages can only be propagated in the same virtual subnet, and cannot be propagated across subnets. The retransmission and the major server are not in the same subnet, and the outgoing subnets need to pass through the pigeon gateway, so they cannot ping each other.