Network cable problems cause PPPOE users to slow down the Internet access speed

Symptom description
A certain Bureau adopts the MA5200 + 2403F networking mode. Due to the small amount of upstream optical resources, the 2403F cascade mode is adopted in the residential area, and the cascade mode adopts five category of twisted pair wires, you can use PPPOE to access the Internet. Some second-level switch users report that the Internet access speed is slow.

Alarm information
There are many CRC verification errors on the upstream port of 2403F.

Cause Analysis
Due to network cable problems, although the port is negotiated to m full duplex, but in fact it cannot be used normally in m full duplex, it can only be used normally in 10 M half duplex.

Handling process
1. perform a test on the second-level corridor switch. If a problem exists, it is very slow to open the local website. PING packets on the computer and find that a large number of packet loss occurs when the packet length exceeds 100. Packet Loss Caused by PING to the public network does not reflect the actual problem. Therefore, PING the virtual template address of MA5200 to test and find that the same problem exists. Now, you can locate the problem from the user side to the MA5200 downstream port side.

2. Check the uplink port status of the second-level switch. The port status is self-negotiation and the negotiation status is M. There are many CRC verification errors on the upstream port. Due to a CRC check error, you can locate the fault and the physical layer.

3. Because there is no such problem between the first-level switch and the MA5200, all the network cables can be located between the first-level switch and the second-level switch. The distance between the first-level switch and the second-level switch is about MB, moreover, the site cannot be changed. Therefore, we can reduce the port negotiation speed to reduce the requirement on the network cable, and try to set the port to 10 MB in full duplex mode. After setting the port, the PING packet will be normal, however, packet loss occurs when the PING packet is downloaded.

4. downgrade the port mode to 10 m half duplex. At this time, the download speed is normal and the PING packet is normal. At this point, the problem is that there is a problem with the network cable between level 1 and level 2 switches, although it can be negotiated to m full duplex, the line actually cannot support m full duplex.

Suggestions and summary
When configuring the business, you must perform PING big package and big business download tests to eliminate physical layer faults.