What is OSPF cost based on?

OSPF relies on costs that are inversely proportional to the bandwidth of the link. Therefore, higher bandwidth links are preferred to lower ones. The Cost formula is reference bandwidth divided by interface bandwidth. The default reference bandwidth of 100 Mbps is used for OSPF cost calculation.

How does OSPF use the cost metric?

The OSPF metric for a route is the sum of the interface costs for all outgoing interfaces in the route. By default, a router’s OSPF interface cost is actually derived from the interface bandwidth: The faster the bandwidth, the lower the cost.

How do you calculate metric cost?

OSPF Metric cost

  1. Cost = Reference bandwidth / Interface bandwidth in bps.
  2. Cost = 108/interface bandwidth in bps.
  3. Default cost of essential interfaces.
  4. Cost of common lines.
  5. Cumulative cost = Sum of all outgoing interfaces cost in route.
  6. Best route for routing table = Route which has the lowest cumulative cost.

How does OSPF increase cost?

Two methods are available to change the OSPF cost. One method is to run the ospf cost command to directly change the interface cost, and the other is to change the bandwidth reference value to indirectly change the interface cost.

What is the default cost of a serial interface with OSPF?

100 / 1.544
With the default of 100 Mbps, and default bandwidth, a serial interface’s default OSPF cost is 100 / 1.544, or 64 (rounded down).

How does OSPF determine cost of interface?

Formula for OSPF cost calculation is:

  1. Interface Cost= Reference bandwidth/interface bandwidth.
  2. Hence By default Interface Cost= 10^8/(interface bandwidth)
  3. The “auto-cost reference-bandwidth” command allows you to change the reference bandwidth that OSPF uses to calculate its metrics:
  4. Router#configure terminal.

What metric is used by OSPF?

cost metric
OSPF uses a cost metric that represents the status of the link and the bandwidth of the interface in an algorithm to determine the best route to a destination. The algorithm used is called the SPF (shortest path first) or Dijkstra algorithm.

What is BGP cost?

The cost community is a nontransitive, extended community attribute that is passed to iBGP and confederation peers, but not to eBGP peers. The configuration of the BGP Cost Community feature allows you to customize the BGP best path selection process for a local autonomous system or confederation.

How does OSPF calculate routes?

OSPF is a dynamic link-state routing protocol that uses a link-state database (LSDB) to build and calculate the shortest path to all known destinations. It is through the use of Dijkstra’s SPF algorithm that the information contained within the LSDB is calculated into routes.

What is N1 and N2 in OSPF?

E1 or E2 or N1 or N2 type routes are based upon cost of the route. E2 or N2 routes tell OSPF routers to set the metric as the metric at the point of redistribution.(At the ASBR) E1 or N1 routes tell OSPF routers to add the internal costs to reach the ASBR to the cost set at the point of redistrbution (At the ASBR)