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Comparing Dynamic Routing Algorithms
Due to the fact that the global link state information is maintained everywhere in a network, LS
algorithms offer a high degree of configuration control and scalability. Changes result in broadcasts
of just the updated information to other routers which means faster convergence and less possibility
of routing loops. OSPF can also operate within a hierarchy, whereas RIP has no knowledge of
sub-network addressing. NetDefendOS uses OSPF as its dynamic routing algorithm because of the
many advantages it offers.
Routing Metrics
Routing metrics are the criteria a routing algorithm uses to compute the "best" route to a destination.
A routing protocol relies on one or several metrics to evaluate links across a network and to
determine the optimal path. The principal metrics used include:
Path length The sum of the costs associated with each link. A commonly used value for
this metric is called "hop count" which is the number of routing devices a
packet must pass through when it travels from source to destination.
Item Bandwidth The traffic capacity of a path, rated by "Mbps".
Load The usage of a router. The usage can be evaluated by CPU utilization and
throughput.
Delay The time it takes to move a packet from the source to the destination. The
time depends on various factors, including bandwidth, load, and the length
of the path.
4.5.2. OSPF
Overview
Open Shortest Path First (OSPF) is a routing protocol developed for IP networks by the Internet
Engineering Task Force (IETF). The NetDefendOS OSPF implementation is based upon RFC 2328,
with compatibility to RFC 1583.
Note: OSPF is not available on all D-Link models
The OSPF feature is only available on the D-Link DFL-800, DFL-860, DFL-1600 and
DFL-2500 product models.
The way OSPF routing functions is that it routes IP packets based only on the destination IP address
found in the IP packet header. IP packets are routed "as is", in other words they are not encapsulated
in any further protocol headers as they transit the Autonomous System (AS). The term Autonomous
System (AS), which is an important concept in OSPF, refers to a single network or group of
networks with a single, clearly defined routing policy controlled by a common administrator.
OSPF is a dynamic routing protocol as it quickly detects topological changes in the AS (such as
router interface failures) and calculates new loop-free routes to destinations.
Link-state Routing
OSPF is a form of link-state routing protocol that defines the sending of link-state advertisements
(LSAs) to all other routers within the same area. Each router maintains a database, known as a
link-state database, describing the AS topology. From the information in this database, each router
constructs a tree of shortest paths with itself as root. This shortest-path tree gives the best route to
each destination in the AS.
4.5.2. OSPF Chapter 4. Routing
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