Hello,
Today, I would like to share with you this topic which describes how to resolve a frequent disconnection on U2000 which occurs after the networking of PTN and Cisco routers.
Fault phenomenon description
The non-gateway network elements NE01 and NE02 respectively communicate with the gateway network element NE03 through a third-party network. Between NE01 and NE03, and between NE02 and NE03, E-Line services are carried through IP tunnels. The physical links are all GE. All three NEs on the U2000 display normal.
When querying NE01 and NE02 on the U2000 network management, both network elements will intermittently go out of control, but NE03 network elements do not have this phenomenon and can operate normally.
Alarm information
no
Steps description
1- On the NMS, PW Ping tests were continuously performed on the PWs of two E-Line services. The test results were normal, and no packet loss occurred in OAM packets.
2- Since there is no problem with the transmission quality, it is important to check the docking configuration of PTN and third-party devices. First confirm the "working mode" of the Ethernet port, no problems were found.
3- Confirm the configuration parameters of the port and service item by item, and finally found that the "MTU" of the third-party device Cisco router is set to 1472, the "Maximum frame length" of the ETH port on the PTN network element main control board is 1620 by default, and the E-Line service the default value of "MTU" is 1500. As a result, some DCN packets sent by PTN NEs are discarded by third-party devices because the packet length exceeds the "MTU" of the third-party devices, and the NEs are unmanaged. The DCN message with a smaller length can be transmitted normally, and the network element resumes communication.
4- Changed the "MTU" of the ETH network port on the NE03 main control board to 1400 to limit the length of the DCN message. The communication of the network element returned to normal, and no further disconnection occurred.
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