OSPF DoNotAge

Question of the day....
How long before this prefix is removed from the OSPF DB

sh ip ospf database router 150.3.7.7

            OSPF Router with ID (150.3.3.3) (Process ID 1)

                Router Link States (Area 0)

  Adv Router is not-reachable
  LS age: 5 (DoNotAge)
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 150.3.7.7
  Advertising Router: 150.3.7.7
  LS Seq Number: 80000002
  Checksum: 0x77FD
  Length: 36
  Area Border Router
  Number of Links: 1

    Link connected to: a Virtual Link
     (Link ID) Neighboring Router ID: 150.3.3.3
     (Link Data) Router Interface address: 155.3.37.7
      Number of TOS metrics: 0
       TOS 0 Metrics: 1


sh ip route 150.3.7.0
% Subnet not in table

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Comments

tigerplug

I think it's one hour by default.
http://tools.ietf.org/rfc/rfc1793.txt

rakem

Yep from the RFC:

Because LSAs with the DoNotAge bit set are never aged, they can
stay in the link state database even when the originator of the
LSA no longer exists. To ensure that these LSAs are eventually
flushed from the routing domain, and that the size of the link
state database doesn't grow without bound, routers are required to
flush a DoNotAge LSA if BOTH of the following conditions are met:

(1) The LSA has been in the router's database for at least
MaxAge seconds.

(2) The originator of the LSA has been unreachable (according to
the routing calculations specified by Section 16 of [1]) for
at least MaxAge seconds.

Cisco MaxAge is 3600 seconds (60 mins) and the refresh timer is 1800 (30 mins)
So they could actually be aged out after 30