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• OSPFv2 is a compatible upgrade to OSPF. It involves enhancements to protocol
message authentication, and the addition of a point-to-multipoint interface which
allows OSPF to run over non-broadcast networks, as well as support for
overlapping area ranges.
• When using OSPF, you must organize your network (i.e., autonomous system) into
normal, stub, or not-so-stubby areas; configure the ranges of subnet addresses
that can be aggregated by link state advertisements; and configure virtual links for
areas that do not have direct physical access to the OSFP backbone.
- To implement OSPF for a large network, you must first organize the network into
logical areas to limit the number of OSPF routers that actively exchange Link
State Advertisements (LSAs). You can then define an OSPF interface by
assigning an IP interface configured on this router to one of these areas. This
OSPF interface will send and receive OSPF traffic to neighboring OSPF routers.
- You can further optimize the exchange of OSPF traffic by specifying an area
range that covers a large number of subnetwork addresses. This is an important
technique for limiting the amount of traffic exchanged between Area Border
Routers (ABRs).
- And finally, you must specify a virtual link to any OSPF area that is not physically
attached to the OSPF backbone. Virtual links can also be used to provide a
redundant link between contiguous areas to prevent areas from being
partitioned, or to merge backbone areas. (Note that virtual links are not
supported for stubs or NSSAs(see definition below).)
Configuring General Protocol Settings
To implement dynamic OSPF routing, first assign VLAN groups to each IP subnet to
which this router will be attached, then use the OSPF / General Configuration menu
to enable OSPF, assign an Router ID to this device, and set the other basic protocol
parameters.
Command Attributes
General Information –
• OSPF Routing Process – Enables or disables OSPF routing for all IP interfaces
on the router. (Default: Disabled)
• OSPF Router ID – Assigns a unique router ID for this device within the
autonomous system. (Default: The lowest interface address)
The router ID must be unique for every router in the autonomous system. Using the
default setting based on the highest interface address ensures that each router ID
is unique. Also, note that the router ID cannot be set to 0.0.0.0 or 255.255.255.255.
If this router already has registered neighbors, the new router ID will be used when
the router is rebooted, or manually restarted using the
no router ospf
command
followed by the
router ospf
command.
• Version Number
21
– The OSPF version number. The OSPF protocol
implemented in this device is based on RFC 2328 (Version 2). It also supports RFC
1583 (early Version 2) compatibility mode.
21. These items are read only.
20-15
Configuring the Open Shortest Path First Protocol
20