Due to nonstandard Network cables, the S3025 user has an abnormal disconnection.

Symptom description
Networking:S3025M is connected to a 5200 m Ethernet port of HAB of 5200 through a M Ethernet port, and users of S3025 are connected to the Internet through VLAN authentication on.

Symptom:After a user obtains an IP address through DHCP under S3025, the user can access the Internet normally. However, after several or ten minutes, the user cannot access the Internet, you must release the address and obtain the IP address again before you can continue accessing the Internet. However, exceptions may occur again in a few or ten minutes.

Alarm information
The Ethernet port information of the S3025 and 5200 connections shows that everything is normal, which is a hundred megabytes of full duplex. 5200 no alarm information.

Cause Analysis
First, the problem of 5200 dhcp server is ruled out. Because the user can access the Internet normally at the beginning, it indicates that the user can obtain the IP address. However, the problem may be caused by an abnormal disconnection in the future, this may be related to interactive packets. It is estimated that 5200 of the monitoring messages for online users have a problem somewhere, so that 5200 considers that the user is offline and actively releases the user's Internet access permission, leading to abnormal disconnection of the user.

Handling process
1. First, check the real-time information of the S3025 port and find that the Ethernet port connecting S3025 and 5200 is normal. This indicates that the port has no problems.

2. You can use a PC to connect to S3025 without having to access the Internet. However, after a while, exceptions may occur and packets are captured on the PC. Many ARP packets with the target MAC address as the unicast address are found, according to the provisions of the instrument, this ARP packet is not standard, and the MAC address of the common ARP packet is broadcast. This type of ARP packet with the target address unicast is a special packet that 5200 is used to detect online users. After the PC is disconnected, the packets are not captured.

3. Enable the debug dhcp packet on 5200 and find that many DHCP detection packets of ARP are not responded by online users.

4. Replace S3025 with 2403F, and connect to the Internet with a PC under 2403F. It is found that the Internet is normal and there is no disconnection. Packet Capture on the PC also shows that many target MAC servers use unicast ARP packets. At this time, check the Debug DHCP debugging information on 5200 and find that all DHCP detection reports of ARP have responses from online users.

5. It is suspected that S3025 will discard this target MAC as the unicast ARP packet, but this is in conflict with the user's ability to access the Internet, because if 3025 discards the packet, users who access the Internet should not be able to access the Internet at the beginning, and the disconnection time should be fixed. The disconnection time will not be between several minutes and ten minutes.

6. To eliminate the problem of the uplink network cable, replace the S3025 and 5200 Network cables with another network cable. The result shows that the Internet users are normal and there is no abnormal disconnection. Solve the problem.

Suggestions and summary
This problem is relatively hidden, because when S3025 uplink port is connected with an unstandard network cable, you cannot see any exceptions in Port 3025, and you can also access the Internet for a while, the surface looks no different from the normal network cable, so it is difficult to locate. 5200 send ARP unicast detection packets to online users at regular intervals. If no response packet is received for online users for five consecutive times, 5200 considers the user to be offline, proactively releases the user's Internet access permissions. When I use F to access the Internet, there is no abnormal disconnection, And when I use S3025, there will be an abnormal disconnection, And the uplink uses the same network cable. It can be seen that S3025 has higher requirements on the quality of the network cable. If an unstandard network cable is used to connect to it, packet loss may occur, if a 5200-Level Probe packet similar to this type is lost, the user will be dropped abnormally. Therefore, we recommend that you pay special attention to the standard network cable when networking S3025 with S3025. Make sure to make the network cable according to the International Standard line sequence to avoid some inexplicable problems, ensures the stability of network operations.

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