Precautions of setting the cost of a virtual link on an S series switch

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According to RFC, the maximum cost value of a virtual link configured on an S series switch supporting OSPF is 65535. If the cost value is larger than 65535, a virtual link cannot be set up.

Other related questions:
What are the precautions for configuring the cost of a virtual link
Ensure that the cost is not greater than the maximum value, that is 65535, defined in the related RFC. Otherwise, no virtual link can be established.

Why configure OSPF virtual links on S series switches
Question: What are the functions of OSPF virtual links configured on S series switch supporting OSPF? Answer: OSPF virtual links can connect areas that are not physically connected to the backbone area to the backbone area so that these areas can route traffic normally. This function is mainly used to merge networks. Virtual links also improve network reliability by allowing normal routing after the physical connection to the backbone area is down. On actual networks, virtual links are seldom used. Generally, networks are planned properly and areas are seldom physically disconnected from the backbone areas. It is rare that networks are merged without network re-planning. In addition, virtual links are seldom used to enhance the robustness of backbone areas.

OSPF cost of S series switches
The ospf cost command can be executed on an S series switch that supports OSPF to configure the cost required for running the OSPF protocol on an interface. Application scenario: The interface cost can be automatically calculated by OSPF based on the interface bandwidth or manually configured by using the ospf cost command. If the costs and destination IP addresses of multiple routes discovered by one routing protocol are the same, load balancing can be implemented among the routes. Modify interface costs to implement load balancing as required. Configuration impact: If no interface cost is configured by using the ospf cost command, OSPF automatically calculates the interface cost based on the interface bandwidth. The calculation formula is as follows: Cost of the interface = Bandwidth reference value/Interface bandwidth. The integer of the calculated result is the cost of the interface. If the calculated result is smaller than 1, the cost value is 1. Changing the bandwidth reference value can change the cost of an interface. By default, the bandwidth reference value is 100 Mbit/s. Therefore, the default cost value of an Ethernet (100 Mbit/s) interface is 1 (100,000,000/the interface bandwidth). Example: Set the cost required by VLANIF 100 for running OSPF to 65. [HUAWEI] interface vlanif 100 [HUAWEI-Vlanif100] ospf cost 65 Set the cost required by GE0/0/1 for running OSPF to 65. [HUAWEI] interface gigabitethernet 0/0/1 [HUAWEI-GigabitEthernet0/0/1] undo portswitch [HUAWEI-GigabitEthernet0/0/1] ospf cost 65 Note: The cost calculated by OSPF is the cost of the route to the outbound interface of the destination network.

Whether virtual TE links must be configured
Virtual TE links need to be created only in specific scenarios. 1. When optical NEs and electrical NEs are separate from each other, a virtual TE link needs to be created between an optical NE and an electrical NE. When an ultra-long span uses an ESC instead of an OSC (for optical-layer ASON only), a virtual TE link needs to be created between NEs at the two ends of the span. When ASON links pass through a traditional NE, virtual TE links need to be created between the traditional NE and ASON NEs. 2. When optical NEs and electrical NEs are separate from each other on an optical-layer ASON network, virtual TE links must be manually configured for OSN 6800/8800 of a version earlier than V100R007C02. Version V100R007C02 and later version support automatic discovery of virtual TE links (this function can be disabled if desired).

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