Block flooding of outbound LSAs on specific OSPF interfaces
By default, the device floods all outbound LSAs on all the OSPF interfaces within an area. You can configure a filter to block outbound
LSAs on an OSPF interface. This feature is particularly useful when you want to block LSAs from some, but not all, of the interfaces
attached to the area.
This command blocks all outbound LSAs to provide options for selective blocking of LSAs.
After you apply filters to block the outbound LSAs, the filtering occurs during the database synchronization and flooding. When a filtering
configuration is changed on a interface, all adjacencies on the interface are set to the Extstart state to restart the database exchange
process. In cases where an LSA has already been flooded on an interface prior to application of the LSA filter, the LSA will not be flushed
out from the remote neighbors. In this situation the user must clear the link state database and the adjacencies on all remote neighbors to
flush out the leaked LSAs or wait for the LSAs to be aged out.
If you remove the filters, the blocked LSAs are automatically re-flooded. You do not need to reset OSPF to re-flood the LSAs.
NOTE
You cannot block LSAs on virtual links, and LSA filtering is not supported on sham
links.
To apply a filter to an OSPF interface to block flooding of outbound LSAs on the interface, enter the following command at the Interface
configuration level for that interface.
device(config-if-e10000-1/1/1)# ip ospf database-filter all out
The command in this example blocks all outbound LSAs on the OSPF interface configured on port 1/1/1.
Syntax:
[no] ip ospf database-filter
{
all
|
all-external
[
allow-default
|
allow-default-and-type4
] |
all-summary-external
[
allow-default
|
allow-default-and-type4
] }
out
The
all
parameter directs the router to block all outbound LSAs on the OSPF interface.
The
all-external
option directs the router to allow the following LSAs: Router, Network, Opq-Area-TE, Opq-Link-Graceful and Type-3
Summary while it blocks all Type-4 and Type-5 LSAs unless directed by one of the following keywords:
allow-default
- allows only Type-5 default LSAs.
allow-default-and-type4
- allows Type-5 default LSAs and all Type 4 LSAs.
The
all-summary-external
option directs the router to allow the following LSAs: Router, Network, Opq-Area-TE and Opq-Link-Graceful
while it blocks all Type-3, Type-4 and Type-5 LSAs unless directed by one of the following keywords:
allow-default
- allows only Type-3 or Type-5 default LSAs.
allow-default-and-type4
- allows Type-3 or Type-5 default LSAs and all Type 4 LSAs.
All Type-7 LSAs are always filtered if the
ip ospf database-filter
command is enabled.
By default, OSPF LSA filtering is disabled on all interfaces.
To remove the filter, enter a command such as the following.
device(config-if-e10000-1/1/1)# no ip ospf database-filter all out
Assign virtual links
All ABRs (area border routers) must 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.
Configuring OSPF
FastIron Ethernet Switch Layer 3 Routing
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