Building network automation solutions

The area area default-cost number router configuration command changes the cost of the default route advertised into a stub or NSSA area. IOS documentation claims the cost is a 24-bit number (and both type-3 and type-5/7 LSAs have 24 bits available for the metric), but in reality the router accepts a 24-bit number and remembers the lower 16 bits, potentially resulting in quite unexpected behavior (just try setting the OSPF costs to 30000 on one ABR and 70000 on another).

Update (2008-08-08): This behavior is reported as bug CSCsl12946 and fixed in IOS release 12.4(20)T.

Here is a sample printout taken from a router running IOS release 12.4(15)T5; 12.2(33)SRC behaves identically.

A1(config)#router ospf 1
A1(config-router)#area 11 default-cost 65538

A1#show running | sect router ospf
router ospf 1
 log-adjacency-changes
 area 11 stub
 area 11 default-cost 2

A1#show ip ospf 1 database summary 0.0.0.0

            OSPF Router with ID (10.0.1.1) (Process ID 1)

                Summary Net Link States (Area 11)

  LS age: 16
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 0.0.0.0 (summary Network Number)
  Advertising Router: A1
  LS Seq Number: 80000005
  Checksum: 0x4CE0
  Length: 28
  Network Mask: /0
        TOS: 0  Metric: 2