Assign a totally stubby area
By default, the device sends summary LSAs (LSA type 3) into stub areas. You can further reduce the number of link state
advertisements (LSA) sent into a stub area by configuring the device to stop sending summary LSAs (type 3 LSAs) into the area. You can
disable the summary LSAs when you are configuring the stub area or later after you have configured the area.
This feature disables origination of summary LSAs, but the device still accepts summary LSAs from OSPF neighbors and floods them to
other neighbors. The device can form adjacencies with other routers regardless of whether summarization is enabled or disabled for
areas on each router.
When you enter a command or apply a Web management option to disable the summary LSAs, the change takes effect immediately. If
you apply the option to a previously configured area, the device flushes all of the summary LSAs it has generated (as an ABR) from the
area.
NOTE
This feature applies only when the device is configured as an Area Border Router (ABR) for the area. To completely prevent
summary LSAs from being sent to the area, disable the summary LSAs on each OSPF router that is an ABR for the area.
To disable summary LSAs for a stub area, enter commands such as the following.
device(config-ospf-router)# area 40 stub 99 no-summary
Syntax:
[no] area
{
num
|
ip-addr
stub
cost
[
no-summary
] }
The
num
and
ip-addr
parameters specify the area number, which can be a number or in IP address format. If you specify a number, the
number can be from 0 - 2,147,483,647.
The
stub
cost
parameter specifies an additional cost for using a route to or from this area and can be from 1 - 16777215. There is no
default. Normal areas do not use the cost parameter.
The
no-summary
parameter applies only to stub areas and disables summary LSAs from being sent into the area.
Assign a Not-So-Stubby Area (NSSA)
The OSPF Not So Stubby Area (NSSA) feature enables you to configure OSPF areas that provide the benefits of stub areas, but that also
are capable of importing external route information. OSPF does not flood external routes from other areas into an NSSA, but does
translate and flood route information from the NSSA into other areas such as the backbone.
NSSAs are especially useful when you want to summarize Type-5 External LSAs (external routes) before forwarding them into an OSPF
area. The OSPF specification (RFC 2328) prohibits summarization of Type-5 LSAs and requires OSPF to flood Type-5 LSAs
throughout a routing domain. When you configure an NSSA, you can specify an address range for aggregating the external routes that
the NSSA's ABR exports into other areas.
The implementation of NSSA is based on RFC 1587.
Configuring OSPF
FastIron Ethernet Switch Layer 3 Routing
53-1003627-04
235
Summary of Contents for FastIron SX 1600
Page 2: ...FastIron Ethernet Switch Layer 3 Routing 2 53 1003627 04 ...
Page 16: ...FastIron Ethernet Switch Layer 3 Routing 16 53 1003627 04 ...
Page 20: ...FastIron Ethernet Switch Layer 3 Routing 20 53 1003627 04 ...
Page 142: ...FastIron Ethernet Switch Layer 3 Routing 142 53 1003627 04 ...
Page 150: ...FastIron Ethernet Switch Layer 3 Routing 150 53 1003627 04 ...
Page 200: ...FastIron Ethernet Switch Layer 3 Routing 200 53 1003627 04 ...
Page 214: ...FastIron Ethernet Switch Layer 3 Routing 214 53 1003627 04 ...
Page 350: ...FastIron Ethernet Switch Layer 3 Routing 350 53 1003627 04 ...
Page 476: ...FastIron Ethernet Switch Layer 3 Routing 476 53 1003627 04 ...
Page 588: ...FastIron Ethernet Switch Layer 3 Routing 588 53 1003627 04 ...