What are the functions of OSPF virtual links

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From the perspective of a protocol, the functions of OSPF virtual links are as follows:

Areas not physically connected to the backbone area can be connected to the backbone area through virtual links so that these areas route traffic normally. This function is mainly used to merge networks.
Virtual links improve network reliability by allowing for 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 backbone areas are seldom physically disconnected from the backbone areas. It is rare that networks are merged without network re-planning. In addition, on actual networks, virtual links are seldom used to enhance the robustness of backbone areas.

Other related questions:
What are the functions of OSPF virtual links
From the perspective of a protocol, the functions of OSPF virtual links are as follows: Areas not physically connected to the backbone area can be connected to the backbone area through virtual links so that these areas route traffic normally. This function is mainly used to merge networks. Virtual links improve network reliability by allowing for 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 backbone areas are seldom physically disconnected from the backbone areas. It is rare that networks are merged without network re-planning. In addition, on actual networks, virtual links are seldom used to enhance the robustness of backbone areas.

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.

What is an OSPF sham link and what is the function of an OSPF sham link
In Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) configuration, OSPF is used as the routing protocol between PEs and CEs so that the sites in a VPN can be connected through the MPLS backbone network. Though the connectivity between OSPF PEs and CEs ensures the connectivity between VPN sites, the backdoor link between VPN sites should also be considered. For two sites to the same site, the path through the backdoor link is always preferred because, according to OSPF specifications, an intra-area path is always preferred to an inter-area path. Therefore, when a backdoor link exists, consider controlling routes through policies. If the backdoor link is used for backup only but is not used to provide VPN services, the default processing flow will be unacceptable. For connections to be re-established between sites through the MPLS VPN backbone area, a logical intra-area link must be established between the ingress and egress Virtual Routing and Forwarding (VRF) interfaces of the related PEs. This feature provides a solution to establish an OSPF sham link between two sites as an intra-area channel so that the two sites communicate with each other through the MPLS backbone area, while the backdoor link is used for backup. If no backdoor link exists between the two sites, no sham link is needed.

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.

Functions of a virtual bridge
The concept of a virtual bridge (VB) was innovatively put forward by Huawei. The switching domain of an Ethernet board that has Layer 2 switching capabilities can be divided into multiple sub-switching domains. If no services are interconnected, different VBs cannot gain access to each other. Each VB has an independent configuration mode and uses an independent VLAN. Different VBs can use the same VLAN.

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