D-Link DFL-1600 User Manual page 93

10.3. Routing Algorithms
rest, runs the LS algorithm and can calculate a same set of least-cost paths
as all the other routers. Any change of the link state will be sent everywhere
in the network, so that all routers keep the same routing table information.
Open Shortest Path First(OSPF) is a commonly used LS algorithm. An
OSPF enabled router identifies the routers and subnets that are directly
connected to it first. Then, it broadcasts the information to all the other
routers. Each router uses the information it received to build a table of
what the whole network looks like. With an complete routing table at
hand, each router can identify the subnetworks and routers that lead to any
specific destination. The OSPF routers only broadcast updated information
when there is any change instead of the whole table.
OSPF depends on various metrics for path determination, including hops,
bandwidth, load, delay, and so on. User customized criteria is also allowed
to be defined for the algorithm, which provides the network administrators
greater control over the routing process. More details about OSPF
algorithm are covered in
Comparison
Link state algorithm, because of its global link state information maintained
everywhere in a network, has high degree of configuration control and
scalability. It responses to changes by broadcasting only the updated
information to all the others, and hence providing faster convergence and
smaller possibility of routing loops. OSPF can also operate within a
hierarchy, while RIP has no knowledge of subnetwork addressing. On the
other hand, OSPF demands relatively higher cost, i.e. more CPU power
and memory, than RIP, therefore, can be more expensive to implement.
D-Link firewalls deploy OSPF as the dynamic routing algorithm.
Routing metrics
Routing metrics(the costs) are the criterion a routing algorithm uses to
compute the "best" route. The main considerations for successful packet
forwarding include the following:
Path length
– Path length is the sum of the costs associated with each link. A
commonly used value for this metric is called hop count, the number
of routing devices, i.e. routers/firewalls, through the path that a
packet takes to travel from the source to its destination.
10.3.3 OSPF.
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