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Knowledge Base

After an Access Switch Is Connected to the Core Switch, the Terminals Connected to the Access Switch Experience Low Internet Access Speeds.

Publication Date:  2019-06-27  |   Views:  247  |   Downloads:  0  |   Document ID:  EKB1100020240


Issue Description

After an access switch S6500 is connected to the core switch, the terminals connected to the access switch experience extremely low Internet access speeds.

Handling Process

1. Run the display interface brief command to check the interface status. The command output shows that the inbound and outbound bandwidth of GE0/0/25 both reaches 99% or higher.

2. The bandwidth of GE0/0/25 is exhausted.

Root Cause

The port bridge enable command is configured on the GE0/0/25 interface of both devices. This command cannot be applied to interfaces that are connected to devices with the Layer 2 forwarding capability. This configuration causes a loop between the two interfaces, affecting all other interfaces that belong to the same VLAN as the two interfaces.
The switch port bridge function applies to the following scenarios: 
1. When a switch is connected to devices that do not have the Layer 2 forwarding capability, and the users connected to the devices need to communicate with each other, the packets are directly sent to the switch for forwarding. In this scenario, you need to enable the port bridge function so that the interface can forward packets whose source and destination MAC addresses are both learned on the interface.    
2. An access switch is deployed in the data center to connected to servers. Multiple VMs are enabled on one server, and data exchange is required between the VMs. To improve the data exchange speed and server performance, you can enable the port bridge function so that the switch can forward data.


Disable the port bridge function on the interfaces by running the following command:

undo port bridgenable

interface  GigabitEthernet 0/0/25

undo port bridgenable


Exercise caution when configuring the port bridge function. Note that if the function is used in inappropriate scenarios, packets may be received and sent through a same interface, causing a loop.