September 18, 2023

20 reasons why office network is not available, as far as you know

As a weak current engineer, we all know that network is one of most inseparable systems in our intelligent system. There will be various failures in network. The most common failure is a network failure. What are reasons?

Let's analyze below what causes network failure:

1. Physical link failure;

The physical connection between computer terminal and switch is normal, that is, there is a problem with manufacturing method of network die, and network generally uses 568B type.

2. Device port failure

Not described here.

3. PC1 and PC2 in same network segment are not connected

Let's troubleshoot hardware device and connection failure first. What could be reason?

(1) Whether network settings, including IP address and subnet mask, are configured correctly, and gateway cannot be configured on same LAN and connected to Internet.

(2) Whether network card is enabled.

(3) Whether port isolation is configured on switch.

(4) The MAC address is bound to switch port, and associated MAC address is not MAC address of computer terminal.

(1) The maximum number of MAC addresses configured on switch is 1.

4. PC1 and PC3 network in different network segments is unavailable

Let's fix hardware and communication failures. What are possible reasons?

(1) Computer terminal gateway address not set;

(2) The port connected to computer terminal is not configured as an access port on switch and has been added to appropriate Vlan.

(3) The switch does not have a vlan address configured, i.e. switch does not have a routing table with two address segments.

(4) MAC address, port and IP address are bound to switch

(5) The switch uses MUX-VLAN technology, which restricts mutual access between VLANs.

Five, PC3 and Internet not connected

The main reasons for disconnection between computer terminal and Internet are as follows. Let's discuss whether this is case together.

(1) DNS is not configured or configured incorrectly on computer terminal.

(2) There is a problem with cable connecting WAN and LAN ports of R1.

(3) There was a problem with R1's intranet address configuration.

(4) There was a problem with egress route configured from switch SW1 to Internet.

(5) Reverse route to 2 VLANs is not configured on R1.

(6) ACLs are configured on routers or switches to restrict access to computer terminals.

(7) External network debt is blocked.

(8) Carrier network failure.

(9) If your home network is not available, there may be a problem setting up your PPPOE dial-up connection.

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