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STP convergence cause the service down for 30 seconds

Publication Date:  2013-05-20 Views:  6 Downloads:  0
Issue Description
When the link between the NE40E router and the RNC is faulty, the traffic is interrupted for 30s.
NE40E version: V600R001C00SPC800



Alarm about STP

Handling Process


In the initial state, MSTP is not enabled on the RNC-109 device, but MSTP is enabled on routers 110 and 111. The RNC-109 device transmits MSTP packets of routers transparently, and STP is generated through the calculation. The calculated result is that 1/0/23 on router 110 is blocked.


When a fault occurs on the link between the RNC-109 device and router 111, STP packets of router 111 cannot be sent to 1/0/3 of router 110 through 2/0/0. Router 110, however, cannot detect a link fault. Before a root interface ages, an interface remains as the root interface. When 1/0/3 ages, STP configures the root interface of 1/0/3 as a designated interface, 1/0/3 remains blocked.


The peer of interface 1/0/3 cannot respond to the STP packets. The interface waits for the forward-delay (by default, the forward-delay is 15s) and then enters the learning state


After waiting for another forward-delay, the interface enters the forwarding state and the traffic is transmitted again. As a result, services are interrupted for 30s.















Root Cause

The configration is incorrect

Solution
If we enable STP in Router port connecting to RNC, when the link between Router and RNC was down, the service will be interrupted for 30s cause STP convergence.
To resolve this problem, we need to disable STP function in the port connecting to RNC device.

Suggestions
- Do not enable STP on the NE40E in this case
- Disable STP on the interface connecting the NE40E and the RNC

END