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Network Description: The network is two NE40E-X8 connected to each other through Eth - Trunk,which contains member GE link 1/0/22,1/0/23,8/0/22,8/0/23.
Version information: NE40E & 80E V600R007C00SPC300
Operation background: The operation content is to replace one NE40E-X8's Slot 1 and Slot 8 to the LPUG-21 board.
Problem Description: After the LPUG board of Slot1 replaced to LPUG -21 board, the Outbound direction port utilization of port 1/0/23 was becoming abnormally high, nearly 100 % (as shown in the following figure).
Avoiding method: The current network has the traffic which across this Eth-Trunk. To avoid the Eth-Trunk link congestion after Shutdown the defective member link,we add port 1/0/20 into the Eth-Trunk instead of port 1/0/23. After replacing, each member link utilization is normal.
Root Cause Analysis: Firstly,check if there is a loop which lead to the broadcast storm. Secondly,confirm if the reason is the unequal Eth-trunk load-sharing.
Location root cause steps:
1. Check the configuration of Eth-Trunk and member links, and also the service side configuration,confirmed that there is no loop,so we excluded the broadcast storm probability;
2. Undoshutdown port1/0/23, check Eth-Trunk forwarding table, we found the load sharing is equal and normal(as shown in the following figure).
3 Shutdown port 1/0/23, check the Eth-Trunk forwarding table, also found the load sharing is equal and normal(as shown in the following figure):
4. Till now,both the 2 probabilities mentioned in 'Root Causes Analysis'are excluded. The root cause analysis return to the physical plane. After board replacing, the board is 40 GE fixed electrical port board, using UTP cable. Tred to reseat the calbe,the problem still persists.
5. Use command 'display interfacegi 1/0/23 ,to check the port detailed information, we found the current bandwidth of this port is only 100M,not 1G(as shown in the following figure).
6. After replaced the board,the port integrated on the board is Gigabit electrical port,which demands high quality UTP cable to match, at least Super-5 class twisted pair is needed,otherwise,it will cause the negotiation status unstable, or only can be negotiated to 100M or not UP.
The UTP Cable quality using in Port 1/0/23 is unqualified, resulting in a Gigabit electrical port automatically negotiated to 100M, which shows the port high utilization artefact.
1. Once encountered such problems,fistly try to find possible causes from the surface phenomenon, and do analysis, the process is OK. However, when the superfical causes are excluded, we should convert thinking immediately to another angle to consider problems, avoiding to fall into the appearances trap;
2. Such Gigabit electrical auto-negotiation to 100M, the common cause is UTP cable unqualified(especially the crystal head) or equipment port impedance mismatch.