Intel 480T, User Manual

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C H A P T E R 1 1 RIP and OSPF
The CLI command to control the NSSA function is similar to the
command used for configuring a stub area, as follows:
config ospf area <area_id> nssa {summary |
nosummary} stub-default-cost <cost> {translate}
The
translate
option determines whether type 7 LSAs are
translated into type 5 LSAs. When configuring an OSPF area as an
NSSA, the
translate
should only be used on NSSA border
routers, where translation is to be enforced. If
translate
is not
used on any NSSA border router in a NSSA, one of the ABRs for
that NSSA is elected to perform translation (as indicated in the
NSSA specification). The option should not be used on NSSA
internal routers. Doing so inhibits correct operation of the election
algorithm.
Normal Area
A normal area is an area that is not any of the following:
• Area 0
• Stub area
• NSSA
Virtual links can be configured through normal areas. External
routes can be distributed into normal areas.
Virtual Links
In the situation when a new area is introduced that does have a direct
physical attachment to the backbone, a
virtual link is used. A virtual
link provides a logical path between the ABR of the disconnected
area and the ABR of the normal area that connects to the backbone.
A virtual link must be established between two ABRs that have a
common area, with one ABR connected to the backbone. Figure 21
illustrates a virtual link.