OSPF Do Not Age (DNA) Flag
In an OSPF topology, some routes within the LSDB may have their "Do Not Age" or DNA flag set. This flag is used to prevent the LSA from aging out. In other words, the LSA remains within the LSDB indefinitely until explicitly removed, or until the OSPF process is removed, or the device is reset.
OSPF's DNA flag is typically set for LSAs for Demand Circuits or LSAs learned over a virtual link. This is done to ensure that these LSAs persist as long as possible over the network.
This is done for several reasons:
- To preserve stability for long lived LSAs
- To reduce unnecessary overhead on links P2P and virtual links
- To ensure persistence during network transitions in large and complex OSPF networks
- To avoid unnecessary LSA flooding ensuring efficient usage of limited network capacities
Links
https://forum.networklessons.com/t/how-to-configure-ospf-virtual-link/942/104?u=lagapidis