Broken network, in addition to using the ping command, what can I do?
If the network is disconnected, it must be Ping gateway first. If it can ping, then the problem will occur in the gateway to the network operator. In this case, the fault will be reported to the operator. However, if the Ping fails, the problem will occur in the internal network of the enterprise. How do you locate such faults? Don't worry, let me introduce ping first.
The role of Ping is to test whether the network from the host/switch to an IP address is unobstructed. Ping is implemented based on the ICMP protocol. After the ICMP Request message is sent from the source to the destination, the destination end is reachable based on whether the ICMP Echo Reply packet is received.
That is, the source port receives the ICMP echo reply message returned by the destination port within a valid time (before waiting for the response timeout time of the echo reply message), indicating that the destination port is reachable. If no response packet is received within the valid time, the destination is unreachable. For the reachable destination, the quality of the link is determined according to the number of sent packets and the number of received response packets. The distance between the source and destination is determined according to the round-trip time of the Ping packet.
Fault location process
If there is more than one device between the PC and the enterprise gateway, it is recommended to execute the Ping command in sections to find the approximate location of the fault and then perform detailed positioning.
Check the configuration. If it is a configuration problem, modify the configuration and see if the fault is restored.
Check the link. If it is a link problem, check if the fault is recovered after troubleshooting.
Check the route . If there is no route to the destination IP, troubleshoot the route.
Check the ARP. Direct link to check whether the ARP entry is learned. If it is not learned, first rule out ARP learning failure.
Check the sending and receiving of messages. There are many ways to check, including: ICMP statistics, IP layer debugging, CPCAR statistics, traffic statistics, mirroring, etc.
Troubleshooting ideas
1.check the configuration
Check whether the port configuration, VLAN configuration, VLANIF interface configuration, and IP address configuration on the switch are correct. Check whether the port type and VLAN encapsulation mode are the same. Check whether the network segment configured with the IP address of the VLANIF interface is faulty.
2.Detection link
Physical link:
The port to which the fiber or network cable is connected needs to be the same as the network required.
The wavelength parameters of the optical modules of the optical fiber must be the same. The Huawei certified optical module is recommended for the optical module.
If the device is connected to an Eth-Trunk interface, the number of physical member ports to be added to the Eth-Trunk must be the same. If the Eth-Trunk is enabled with LACP, you need to ensure that the LACP status is stable.
Check whether there is a transmission device between the two devices and check whether the physical ports on both ends are in the Up state.
Check whether the physical port passing through the ping service has a CRC check error and the error count is increasing.
Check the physical port for blocking. Check whether the Layer 2 protocol such as STP, RRPP, or SMART LINK is running on the device. Check whether the physical port through which the ping service passes is blocked.
Route detection checks whether there is a route to the ping destination address on the device. Reference command: "display ip routing-table".
If the terminal device is connected to the switch, check whether the correct gateway address is configured on the terminal device. If a switch or routing device is connected to the switch, check that there is a correct return route on the peer device. If the route is not normal, check whether the interface protocol status is Up, whether the routing protocol running on the device is normal, and check the route fault.
Check ARP entries
1.Check whether the ARP of the directly connected address is normal. Related commands:
display arp
display arp interface vlanif vlanif-id
2.If the ARP learning is correct, check the MAC address entry to check whether the outbound port of the MAC address is the same as the physical outbound port
display mac-address mac-address display mac-address mac-address vlan vlan-id
3.Check if you can learn arp, if you can not please troubleshoot:
Check whether the strict learning arp is configured, please remove and try again
Re-learn arp through ping operation.
Check the sending and receiving of packets
If the ping fails or there is a packet loss problem, the key to the positioning is to confirm where the packet is lost. You can confirm it in the following ways:
ICMP statistics
CPCAR statistics
The role of Ping is to test whether the network from the host/switch to an IP address is unobstructed. Ping is implemented based on the ICMP protocol. After the ICMP Request message is sent from the source to the destination, the destination end is reachable based on whether the ICMP Echo Reply packet is received.
That is, the source port receives the ICMP echo reply message returned by the destination port within a valid time (before waiting for the response timeout time of the echo reply message), indicating that the destination port is reachable. If no response packet is received within the valid time, the destination is unreachable. For the reachable destination, the quality of the link is determined according to the number of sent packets and the number of received response packets. The distance between the source and destination is determined according to the round-trip time of the Ping packet.
Fault location process
If there is more than one device between the PC and the enterprise gateway, it is recommended to execute the Ping command in sections to find the approximate location of the fault and then perform detailed positioning.
Check the configuration. If it is a configuration problem, modify the configuration and see if the fault is restored.
Check the link. If it is a link problem, check if the fault is recovered after troubleshooting.
Check the route . If there is no route to the destination IP, troubleshoot the route.
Check the ARP. Direct link to check whether the ARP entry is learned. If it is not learned, first rule out ARP learning failure.
Check the sending and receiving of messages. There are many ways to check, including: ICMP statistics, IP layer debugging, CPCAR statistics, traffic statistics, mirroring, etc.
Troubleshooting ideas
1.check the configuration
Check whether the port configuration, VLAN configuration, VLANIF interface configuration, and IP address configuration on the switch are correct. Check whether the port type and VLAN encapsulation mode are the same. Check whether the network segment configured with the IP address of the VLANIF interface is faulty.
2.Detection link
Physical link:
The port to which the fiber or network cable is connected needs to be the same as the network required.
The wavelength parameters of the optical modules of the optical fiber must be the same. The Huawei certified optical module is recommended for the optical module.
If the device is connected to an Eth-Trunk interface, the number of physical member ports to be added to the Eth-Trunk must be the same. If the Eth-Trunk is enabled with LACP, you need to ensure that the LACP status is stable.
Check whether there is a transmission device between the two devices and check whether the physical ports on both ends are in the Up state.
Check whether the physical port passing through the ping service has a CRC check error and the error count is increasing.
Check the physical port for blocking. Check whether the Layer 2 protocol such as STP, RRPP, or SMART LINK is running on the device. Check whether the physical port through which the ping service passes is blocked.
Route detection checks whether there is a route to the ping destination address on the device. Reference command: "display ip routing-table".
If the terminal device is connected to the switch, check whether the correct gateway address is configured on the terminal device. If a switch or routing device is connected to the switch, check that there is a correct return route on the peer device. If the route is not normal, check whether the interface protocol status is Up, whether the routing protocol running on the device is normal, and check the route fault.
Check ARP entries
1.Check whether the ARP of the directly connected address is normal. Related commands:
display arp
display arp interface vlanif vlanif-id
2.If the ARP learning is correct, check the MAC address entry to check whether the outbound port of the MAC address is the same as the physical outbound port
display mac-address mac-address display mac-address mac-address vlan vlan-id
3.Check if you can learn arp, if you can not please troubleshoot:
Check whether the strict learning arp is configured, please remove and try again
Re-learn arp through ping operation.
Check the sending and receiving of packets
If the ping fails or there is a packet loss problem, the key to the positioning is to confirm where the packet is lost. You can confirm it in the following ways:
ICMP statistics
CPCAR statistics
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