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How does OSPF choose best path?

If there are multiple routes to a network with the same route type, the OSPF metric calculated as cost based on the bandwidth is used for selecting the best route. The route with the lowest value for cost is chosen as the best route.

What is Asbr in OSPF?

In OSPF, routers always form the boundaries between areas. A router with links outside the OSPF routing domain is called an autonomous system boundary router (ASBR). Routing information about destination IP addresses not learned from OSPF are always advertised by an ASBR.

How do I setup Asbr on my router?

Configure an ASBR Router

  1. Configure a router as an ASBR. SEFOS(config)# ipv6 router ospf SEFOS(config-router)# asbr router SEFOS(config-router)# end.
  2. Ensure that the router is configured as an ASBR.

How does OSPF determine priority?

You can verify which neighbors are the DR/BDR/DROTHER by using the show ip ospf neighbor command in privileged mode. Configures an OSPF priority on a per interface basis used to manipulate the DR/BDR election process.

How is OSPF calculated?

Open Shortest Path First (OSPF) uses “Cost” as the value of metric and uses a Reference Bandwidth of 100 Mbps for cost calculation. The formula to calculate the cost is Reference Bandwidth divided by interface bandwidth. For example, in the case of 10 Mbps Ethernet , OSPF Metric Cost value is 100 Mbps / 10 Mbps = 10.

Does OSPF use TCP or UDP?

Because OSPF does not use UDP or TCP, the OSPF protocol is fairly elaborate and must reproduce many of the features of a transport protocol to move OSPF messages between routers.

How do I enable OSPF on my router?

To enable OSPF on a Cisco router and advertise interfaces, the following tasks are required:

  1. Use the command router ospf process ID to start OSPF.
  2. Use the network command to enable the interfaces.
  3. Identify area assignments.
  4. (Optional) Assign the router ID.

What is OSPF wait time?

The Wait Timer is used in OSPF to allow newly-booted routers to determine the DR/BDR on their multiaccess segments. It allows these routers to wait to see if any DR/BDRs exist on those links, before declaring themselves as the DR/BDR.

How does OSPF determine DR?

Two rules are used to elect a DR and BDR:

  1. router with the highest OSPF priority will become a DR. By default, all routers have a priority of 1.
  2. if there is a tie, a router with the highest router ID wins the election. The router with the second highest OSPF priority or router ID will become a BDR.

Which is route selection mechanism in OSPF Type 5?

This document describes the Open Shortest Path First (OSPF) Link State Advertisement (LSA) Type 5 External Route Selection mechanism. It presents a network scenario with the configuration for how to select the route received from one Autonomous System Boundary Router (ASBR) over another.

Why does OSPF prefer one ASBR over another?

The net difference is that if you redistribute an E2 route at two ASBRs and configure the redistribution cost to be lower on one of these ASBRs, your whole OSPF domain will prefer this ASBR, no matter how far that ASBR might be, even if the second ASBR is closer.

How to show OSPF in privileged exec mode?

To display the internal Open Shortest Path First (OSPF) routing table entries to an Area Border Router (ABR) and Autonomous System Boundary Router (ASBR), use the show ip ospf border-routers command in privileged EXEC mode.

What is selection of forwarding address in OSPF-Cisco?

This document describes the concepts used for the selection of forwarding address for an External LSA (Link State Advertisement) by an ASBR (Autonomous System Boundary Router) in OSPF (Open Shortest Path First) domain. Readers of this document should have knowledge of these topics: