What is an ABR

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According to RFC 2328, the OSPF backbone area contains the Area Border Routers (ABRs) of all the areas. That is, an ABR must belong to the backbone area. If area 2 and area 3 are configured on a device but none of the interfaces of the device belongs to the backbone area, the device is not an ABR.

RFC 3509 defines what is an ABR.

In the switch implementation, an ABR can belong to two or more areas, and one of the areas must be a backbone area. For the configuration of these areas, each area does not need to contain at least one interface in the Up state.

Other related questions:
Definition of ABR in OSPF on S series switches
Question: What is the definition of ABR? Is a device with more than two areas configured an ABR? Answer: According to RFC 2328, an OSPF backbone area contains the ABRs of all areas. That is, an ABR must belong to a backbone area. If Area 2 and Area 3 are configured on a device with no interface in a backbone area, the device is not an ABR. If two or more areas are configured on an S series switch supporting OSPF and one of these areas is a backbone area, the switch is an ABR. Not all these areas must have interfaces in the Up state.

Why does an ABR advertise continuous network segment addresses of an area as a summary address
Perform the following steps to solve this problem: 1. Run the display current configuration command to check whether the network segment addresses of the area are continuous. 2. If the network segment addresses are discontinuous, divide them into several groups of continuous network segment addresses. 3. Run the abr-summary command to summarize each group of continuous networks into a single network on the area border router (ABR). 4. In area view, run the filter export command and ensure that the link-state advertisements (LSAs) summarized by the ABR are not filtered out.

Why does not an S series switch functioning as an ABR summarize addresses while advertising the routes
Perform the following operations on the S series switch functioning as the ABR to solve the problem. Run the display current configuration command to check whether all network segments in the area are consecutive. If not, divide the network segments into several groups of consecutive network segments. Run the abr-summary command on the ABR to summarize each group of consecutive network segments into one network segment. Check the filter export command in the area view and ensure that the LSA for ABR route summarization is not filtered out.

Which S series switch will be selected to translate Type 7 LSAs into Type 5 LSAs if multiple ABRs are deployed in an NSSA
Question: When multiple S series switches functioning as ABRs are deployed in an NSSA, which switch will be selected to translate Type 7 LSAs into Type 5 LSAs? Answer: The system automatically selects the ABR with the largest router ID to translate LSAs.

What is AS
Auto Scaling (AS) is a service that automatically adjusts resources based on your service requirements and configured AS policies. You can specify AS configurations and policies based on service requirements. These configurations and policies free you from repeatedly adjusting resources to keep up with service changes and demand peaks, which helps you reduce the required resources and workforce.

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