Open Beeline Aisle First (OSPF)
Dynamic acquisition occurs back accessories acquaint to adjoining devices, allegorical anniversary added of the reachability
of networks. These accessories acquaint application a acquisition agreement such as OSPF to barter avenue information.
Unlike changeless routing, the acquisition advice busy into the acquisition tables is added and deleted dynamically
by a activating acquisition agreement as routes change over time.
OSPF is an Interior Gateway Agreement (IGP) that distributes acquisition advice amid devices. OSPF is used
over IP, and OSPF packets are transmitted with an IP abstracts packet with the agreement acreage in the IP attack set to
89. OSPF uses a link-state algorithm to body and account the beeline aisle to all accepted destinations. The
algorithm acclimated to account the beeline aisle is alleged the Dijkstra algorithm (named afterwards its artist Edsger
W. Dijkstra).
The Security Appliance supports OSPF acquisition agreement in a address agnate to the IOS. The Security Appliance
can run up to two OSPF processes simultaneously, for altered sets of interfaces. By default, the two processes
will not barter advice unless avenue redistribution is configured explicitly. The two processes are isolated,
as in two abstracted acquisition instances in the aforementioned device. There are several affidavit to accept two OSPF processes
on the Security Appliance. For example, two processes on the Security Appliance are advantageous if the Security
Appliance has interfaces that use the aforementioned IP addresses. (NAT allows these interfaces to coexist, but OSPF does
not acquiesce overlapping addresses.) Or, in best cases, a abstracted OSPF action is enabled on the central and the
outside interfaces (as apparent in Figure 6-9), to accord you the adequacy to ascendancy avenue advancement by
redistributing a subset of routes amid the two processes. Similarly, there could be a claim to
segregate clandestine addresses from accessible addresses, authoritative two processes necessary.
Figure 6-9. IP Acquisition Protocols on Security Appliance
[View abounding admeasurement image]
The amount (also alleged metric) of an interface in OSPF is inversely proportional to the bandwidth of that interface.
A college bandwidth indicates a lower cost, and a lower-cost aisle is the adopted route. The blueprint acclimated to
calculate the OSPF amount is
OSPF Amount = 100,000,000 ÷ bandwidth (in bps)
As apparent in Figure 6-9, redistribution amid the two OSPF processes is supported. Changeless and connected
routes on the Security Appliance can additionally be redistributed into the OSPF process, but they charge be configured
on OSPF-enabled interfaces.