HP 7102dl - ProCurve Secure Router Configuration Manual page 889

Other problems with an ABR include:
not sending route summaries to the areas that need them
misrouting inter-area traffic
An ABR That Does Not Send Route Summaries. The area that is not
receiving summaries may be defined as a total stub area. Such areas do not
receive route summaries.
View the running-config and look for this OSPF configuration for the area in
question:
area <area ID> stub no-summary
If the area should be receiving summaries, move to the OSPF configuration
mode context and re-enter the command without the no-summary option:
ProCurve(config-ospf)# area <area ID> stub
The ABR might also be prohibited from advertising a route summary. View the
running-config and look for this option for the area that cannot be reached:
area <area ID> range <network A.B.C.D> <subnet mask> not-advertise
Remove this configuration and re-enter the command with the advertise
option instead.
An ABR Misrouting Inter-Area Traffic. When an ABR generates incor-
rect route summaries, it can both misroute traffic itself and cause connected
stub routers to misroute traffic. Misconfigurations often involve entering the
wrong subnet mask for an area's IP address range.
You can view the summaries the router is sending by entering show ip ospf
database summary from the enable mode context.
In a network with variable-length subnets, you must be very careful to specify
subnet masks that correspond with the correct CIDR prefix length. Remem-
ber, for example, that the network address 172.16.0.0 /16 (255.255.0.0) is
different from the network address, 172.16.0.0 /20 (255.255.240.0). The first
refers to all addresses between 172.16.0.1 through 172.16.255.255; the second
only refers to addresses up to 172.16.15.255.
When the router summarizes routes to a range of subnets, you must alter the
subnet mask that corresponds with the subnet's bit length, which can lead to
errors. The simplest way is to summarize a range of subnets up to the classful
network boundary.
IP Routing—Configuring RIP, OSPF, BGP, and PBR
Troubleshooting Routing
15-163