Ospf Cost - D-Link DES-3326SR Manual

D-Link DES-3326SR Layer 3 Switch

OSPF Cost

Each OSPF interface has an associated cost (also called "metric") that is representative of the overhead required
to send packets over that interface. This cost is inversely proportional to the bandwidth of the interface (i.e. a
higher bandwidth interface has a lower cost). There is then a higher cost (and longer time delays) in sending
packets over a 56 Kbps dial-up connection than over a 10 Mbps Ethernet connection. The formula used to
calculate the OSPF cost is as follows:
Cost = 100,000,000 / bandwidth in bps
As an example, the cost of a 10 Mbps Ethernet line will be 10 and the cost to cross a 1.544 Mbps T1 line will be
64.
Shortest Path Tree
To build Router A's shortest path tree for the network diagramed below, Router A is put at the root of the tree
and the smallest cost link to each destination network is calculated.
Figure 23- 1. Constructing a Shortest Path Tree
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