Demand Circuit

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ISDN BRI

DNA Bit

Suppressed periodic LSA refresh

• Stops the LSA refreshes that occur every

30 minutes in OSPF

• Can be verified through the "show ip ospf database" command

© 2002, Cisco Systems, Inc. All rights reserved. Cisco CCIE Prep v1.0—Module 7-66

Suppressed Periodic LSA Refresh

The periodic Link-State Advertisement (LSA) refreshes that take place every 30 minutes in OSPF do not occur over the demand circuit. When the demand circuit is established, a unique option bit (the DC bit) is exchanged between the neighboring routers. If the two routers negotiate the Direct Current (DC) bit successfully, they will make a note of it and set a specific bit in the LSA Age field of LSAs they receive from the neighbor on the demand circuit. This specific bit is called the DoNotAge (DNA) bit. The DNA bit is the most significant bit in the LS Age field. By setting this bit, the LSA stops aging and no periodic updates are sent.

The setting of the DNA bit on LSAs can be verified by viewing the link-state database with the show ip ospf database command.

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