Routing > OSPF
Routing
RM GUI HiSecOS EAGLE20/30
Release
3.0
09/2015
297
Routing > OSPF
8.9 Open Shortest Path First
OSPF (Open Shortest Path First) version 2, is a routing protocol described in
RFC 2328, which is applicable to networks with many routers.
In contrast to the hop count based distance-vector routing protocols such as
RIP, OSPF provides a link state algorithm. OSPF bases its link state
algorithm on link cost meaning that the criterion for the routing decisions are
the path costs instead of hop counts. The path cost is calculated as
(100 Mbit/s) / (bandwidth in Mbit/s). OSPF also supports Variable Length
Subnet Masking (VLSM) or Classless Inter-Domain Routing (CIDR)
networks.
OSPF convergence of the entire network is slow, but after implementation
the protocol is quick in reacting to topology changes. The convergence time
for OSPF is 5 to 15 seconds, depending on the size of the network.
OSPF supports networks divided into "Areas" and thus reduces the
administrative effort when maintaining the network. The routers participating
in the network know and only manage their own "Area" by flooding Link State
Advertisements (LSAs) into the area. Using the LSAs each router builds its
own topology database.
The Area Border Routers (ABR) and Designated Routers (DR) flood LSAs
in an "Area" informing the local networks about destinations in other areas
within the OSPF domain.
With Hello packets, neighboring routers periodically identify themselves
and signal their availability. If a router misses the hello packets of another
router, then after the expiration of the dead-interval timer, the router
considers this router as unreachable.
The device allows you to use the md5 algorithm for secure data transmission.
When you use the md5 mode, specify the same values on the devices in
same area. Specify the area relevant values connected to the ABRs and
ASBRs.
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