An OSPF interface can be considered to belong to the area that
contains the attached network. All routing protocol packets
originated by the router over this interface are labelled with the
interface's Area ID. One or more router adjacencies may develop
over an interface. A router's link state advertisements reflect the
state of its interfaces and their associated adjacencies.
The following data items are associated with an interface. Note
that a number of these items are actually configuration for the
attached network; those items must be the same for all routers
connected to the network.
- Type
-
The kind of network to which the interface attaches. Its value
is either broadcast, non-broadcast yet still multi-access,
point-to-point or virtual link.
- State
-
The functional level of an interface. State determines whether
or not full adjacencies are allowed to form over the interface.
State is also reflected in the router's link state
advertisements.
- IP interface address
-
The IP address associated with the interface. This appears as
the IP source address in all routing protocol packets originated
over this interface. Interfaces to unnumbered point-to-point
networks do not have an associated IP address.
- IP interface mask
-
Also referred to as the subnet mask, this indicates the portion
of the IP interface address that identifies the attached
network. Masking the IP interface address with the IP interface
mask yields the IP network number of the attached network. On
point-to-point networks and virtual links, the IP interface mask
is not defined. On these networks, the link itself is not
assigned an IP network number, and so the addresses of each side
of the link are assigned independently, if they are assigned at
all.
- Area ID
-
The Area ID of the area to which the attached network belongs.
All routing protocol packets originating from the interface are
labelled with this Area ID.
- HelloInterval
-
The length of time, in seconds, between the Hello packets that
the router sends on the interface. Advertised in Hello packets
sent out this interface.
- RouterDeadInterval
-
The number of seconds before the router's neighbors will declare
it down, when they stop hearing the router's Hello Packets.
Advertised in Hello packets sent out this interface.
- InfTransDelay
-
The estimated number of seconds it takes to transmit a Link
State Update Packet over this interface. Link state
advertisements contained in the Link State Update packet will
have their age incremented by this amount before transmission.
This value should take into account transmission and propagation
delays; it must be greater than zero.
- Router Priority
-
An 8-bit unsigned integer. When two routers attached to a
network both attempt to become Designated Router, the one with
the highest Router Priority takes precedence. A router whose
Router Priority is set to 0 is ineligible to become Designated
Router on the attached network. Advertised in Hello packets
sent out this interface.
- Hello Timer
-
An interval timer that causes the interface to send a Hello
packet. This timer fires every HelloInterval seconds. Note
that on non-broadcast networks a separate Hello packet is sent
to each qualified neighbor.
- Wait Timer
-
A single shot timer that causes the interface to exit the
Waiting state, and as a consequence select a Designated Router
on the network. The length of the timer is RouterDeadInterval
seconds.
- List of neighboring routers
-
The other routers attached to this network. On multi-access
networks, this list is formed by the Hello Protocol.
Adjacencies will be formed to some of these neighbors. The set
of adjacent neighbors can be determined by an examination of all
of the neighbors' states.
- Designated Router
-
The Designated Router selected for the attached network. The
Designated Router is selected on all multi-access networks by
the Hello Protocol. Two pieces of identification are kept for
the Designated Router: its Router ID and its IP interface
address on the network. The Designated Router advertises link
state for the network; this network link state advertisement is
labelled with the Designated Router's IP address. The
Designated Router is initialized to 0.0.0.0, which indicates the
lack of a Designated Router.
- Backup Designated Router
-
The Backup Designated Router is also selected on all multi-
access networks by the Hello Protocol. All routers on the
attached network become adjacent to both the Designated Router
and the Backup Designated Router. The Backup Designated Router
becomes Designated Router when the current Designated Router
fails. The Backup Designated Router is initialized to 0.0.0.0,
indicating the lack of a Backup Designated Router.
- Interface output cost(s)
-
The cost of sending a data packet on the interface, expressed in
the link state metric. This is advertised as the link cost for
this interface in the router links advertisement. There may be
a separate cost for each IP Type of Service. The cost of an
interface must be greater than zero.
- RxmtInterval
-
The number of seconds between link state advertisement
retransmissions, for adjacencies belonging to this interface.
Also used when retransmitting Database Description and Link
State Request Packets.
- Authentication key
-
This configured data allows the authentication procedure to
generate and/or verify the Authentication field in the OSPF
header. The Authentication key can be configured on a per-
interface basis. For example, if the AuType indicates simple
password, the Authentication key would be a 64-bit password.
This key would be inserted directly into the OSPF header when
originating routing protocol packets, and there could be a
separate password for each network.
