Cisco Cisco IOS Software Release 12.4(15)T

OSPF Mechanism to Exclude Connected IP Prefixes from LSA Advertisements

Prerequisites for the OSPF Mechanism to Exclude Connected IP Prefixes from LSA Advertisements

Cisco IOS Release 12.4(15)T

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Additional References, page 10

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Command Reference, page 11

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Feature Information for the OSPF Mechanism to Exclude Connected IP Prefixes from LSA
Advertisements, page 15

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Glossary, page 16

Prerequisites for the OSPF Mechanism to Exclude Connected IP
Prefixes from LSA Advertisements

Before you can use the mechanism to exclude IP prefixes from LSAs, the OSPF routing protocol must
be configured.

Information About the OSPF Mechanism to Exclude Connected
IP Prefixes from LSA Advertisements

One way to improve OSPF network convergence is to limit the number of IP prefixes carried in LSAs.

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Previous Methods to Limit the Number of IP Prefixes Carried in LSAs, page 2

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Feature Overview of the OSPF Mechanism to Exclude Connected IP Prefixes from LSA
Advertisements, page 2

Previous Methods to Limit the Number of IP Prefixes Carried in LSAs

Configuring interfaces as unnumbered limits IP prefixes. However, for network management and the
ease of identifying and troubleshooting numbered interfaces, you might want to have numbered
interfaces and also want to limit the number of IP advertisements.

Feature Overview of the OSPF Mechanism to Exclude Connected IP Prefixes
from LSA Advertisements

The OSPF mechanism to exclude connected IP prefixes from LSAs allows network administrators to
control what IP prefixes are installed into LSAs. This functionality is implemented for router and
network LSAs in the following manner:

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For the router LSA, to exclude prefixes, the feature excludes link type 3 (stub link).

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For the network LSA, the OSPF Designated Router (DR) generates LSAs with a special /32 network
mask (0xFFFFFFFF).

Note

Previous versions of Cisco IOS software that do not have this feature will install the /32 prefix into the
routing table.