Chapter 50
| IP Routing Commands
Open Shortest Path First (OSPFv3)
– 1047 –
abr-type This command sets the criteria used to determine if this router can declare itself an
ABR and issue Type 3 and Type 4 summary LSAs. Use the no form to restore the
default setting.
Syntax
abr-type {cisco | ibm | standard}
no abr-type
cisco - ABR criteria and functional behavior is based on RFC 3509.
ibm - ABR criteria and functional behavior is briefly described in RFC 3509,
and fully documented in IBM Nways Multiprotocol Routing Services (MRS)
3.3.
standard - ABR criteria and functional behavior is based on RFC 2328.
Command Mode
Router Configuration
Default Setting
cisco
Command Usage
â—† The basic criteria for a router to serve as an ABR is shown below:
â–
Cisco Systems Interpretation: A router is considered to be an ABR if it has
more than one area actively attached and one of them is the backbone
area.
â–
IBM Interpretation: A router is considered to be an ABR if it has more than
one actively attached area and the backbone area is configured.
â–
Standard Interpretation: A router is considered to be an ABR if it is attached
to two or more areas. It does not have to be attached to the backbone area.
â—† To successfully route traffic to inter-area and AS external destinations, an ABR
must be connected to the backbone. If an ABR has no backbone connection, all
traffic destined for areas not connected to it or outside the AS will be dropped.
This situation is normally resolved, by configuring a virtual link from the ABR to
the backbone area.
â—† In both the Cisco and IBM interpretation, a router connected to more than one
area cannot issue a Type 1 router LSA declaring itself as an ABR unless it meets
the other criteria listed above.
Routing table calculations are changed to allow the router to consider
summary-LSAs from all attached areas if it is not an ABR, but has more than one
attached area, or it does not have an active backbone connection.
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