How to rectify the unidirectional communication fault on Eth-Trunk of S series switches

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The following features enable you to rectify the unidirectional communication fault on Eth-Trunks of S series switches (except the S1700):
1. 3AH: Monitor the link connectivity through 3AH. If a unidirectional communication fault occurs, the feature ensures the two ends of a link are in the same state.
2. LACP: LACP ensures the same status between the two ends of the Eth-trunk through exchanges of LACPDUs. If a unidirectional communication fault occurs, LACP can detect the fault on time and transfer the selected state to the other side, preventing traffic loss caused by the unidirectional communication fault.
Notes:
S series switches (except the S1700) running V100R005 and later versions support the device link detection protocol (DLDP). DLDP can monitor the link status of fibers or copper twisted pairs. If DLDP detects a unidirectional link, it automatically closes the relevant port or notifies the user to close the port, depending on the user configuration. This prevents network faults.

Other related questions:
How to rectify the unidirectional communication fault on an Eth-Trunk
To rectify the unidirectional communication fault on an Eth-Trunk, the following features are required: 802.3ah: The link connectivity can be detected through 802.3ah. When a unidirectional communication fault occurs, the status of the two ends of the trunk can be the same in time. LACP: Through the exchange of LACPDUs, LACP can ensure that the status of the two ends of the trunk is the same. When a unidirectional communication fault occurs, LACP can detect the fault in time and transfer the selected status to the other side, thus solving the packet loss problem caused by the unidirectional communication fault. NOTE: In V100R005 and later versions, DLDP can monitor the link status of optical fibers or copper twisted-pair cables. If a unidirectional link exists, DLDP automatically disables the interface or prompts the user to manually disable the interface. This prevents network faults.

How load balancing is implemented on S series switches when link aggregation is configured
For S series switches (except the S1700), there are two load balancing modes: per-packet load balancing and per-flow load balancing. 1. Per-packet load balancing mode When there are multiple physical links between the two devices of the Eth-Trunk, the first data frame of a data flow is transmitted on one physical link, and the second data frame is transmitted on another physical link. In this case, the second data frame may arrive at the peer device earlier than the first data frame. As a result, packet mis-sequencing occurs. 2. Per-flow load balancing mode This mechanism uses the hash algorithm to calculate the address in a data frame and generates a hash key value. Then the system searches for the outbound interface in the Eth-Trunk forwarding table based on the generated hash key value. Each MAC or IP address corresponds to a hash key value, so the system uses different outbound interfaces to forward data. This mechanism ensures that frames of the same data flow are forwarded on the same physical link and implements flow-based load balancing. Per-flow load balancing ensures the correct sequence of data transmission, but cannot ensure the bandwidth usage. Notes: Currently, S series switches support only per-flow load balancing mode, including the following: 1. Load balancing based on the source MAC address of packets; 2. Load balancing based on the destination MAC address of packets; 3. Load balancing based on the source IP address of packets; 4. Load balancing based on the destination IP address of packets; 5. Load balancing based on the source and destination MAC addresses of packets; 6. Load balancing based on the source and destination IP addresses of packets; 7. Enhanced load balancing for L2, IPv4, IPv6, and MPLS packets based on the VLAN ID and source physical interface number. When you configure load balancing modes, follow these guidelines: The load balancing mode only takes effect on the outbound interface of traffic. If load is unevenly distributed on the inbound interfaces, change the load balancing mode on the uplink outbound interfaces. Configure load balancing to ensure data flow is transmitted on all active links instead of only one link, preventing traffic congestion and ensuring normal service operation. For example, if data packets have only one destination MAC address and IP address, you are advised to configure load balancing based on the source MAC address and IP address. If you implement load balancing based on the destination MAC address and IP address, the data flow may be transmitted on only one link, causing traffic congestion.

Link aggregation support on S series fixed switches
S series fixed switches (except the S1700) support the link aggregation function. For details about link aggregation support on the fixed switches, see the "Ethernet Switching - Link Aggregation" in the S1720&S2700&S3700&S5700&S6700 Product Use Precautions.

How to delete an Eth-Trunk on S series switches
For S series switches (except the S1700), follow these two steps to delete an Eth-Trunk: 1. Delete member interfaces from the Eth-Trunk. You can select either of the following two methods to delete a member interface. Method 1: Run the undo command in the Eth-Trunk interface view. [HUAWEI] interface eth-trunk 1 [HUAWEI-Eth-Trunk1] undo trunkport gigabitethernet 1/0/1�?Method 2: Run the undo command in the member interface view. [HUAWEI] interface gigabitethernet 1/0/1 [HUAWEI-GigabitEthernet1/0/1] undo eth-trunk�?2. Delete the Eth-Trunk. Run the undo command in the system view. [HUAWEI] undo interface eth-trunk 10

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