IP Routing Features
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Retransmit-interval: The time between retransmissions of link-state adver
tisements (LSAs) to adjacent routers for this interface. The value can be from
0 – 3600 seconds. The default is 5 seconds.
Transit-delay: The time it takes to transmit Link State Update packets on this
interface. The value can be from 0 – 3600 seconds. The default is 1 second.
Assigning Virtual Links
It is highly recommended that all ABRs (area border routers) have either a
direct or indirect link to the OSPF backbone area (0.0.0.0 or 0). If an ABR does
not have a physical link to the area backbone, the ABR can configure a virtual
link to another router within the same area, which has a physical connection
to the area backbone.
A backbone area can be purely virtual with no physical backbone links. Also
note that virtual links can be "daisy chained". If so, it may not have one end
physically connected to the backbone.
The path for a virtual link is through an area shared by the neighbor ABR
(router with a physical backbone connection), and the ABR requiring a logical
connection to the backbone.
Two parameters must be defined for all virtual links—transit area ID and
The transit area ID represents the shared area of the two ABRs and
serves as the connection point between the two routers. This number
should match the area ID value.
The neighbor router field is the router ID (IP address) of the router that
is physically connected to the backbone, when assigned from the router
interface requiring a logical connection. When assigning the parameters
from the router with the physical connection, the router ID is the IP
address of the router requiring a logical connection to the backbone.
By default, the router ID is the lowest numbered IP address configured on the
device. For more information or to change the router ID, see "Changing the
Router ID" on page 5-10.
When you establish an area virtual link, you must configure it on both of the
routers (both ends of the virtual link).