Extreme Networks 200 Series - Manual (Page 213)

Overview of OSPF
Summit 200 Series Switch Installation and User Guide 211
Database Overflow
The OSPF database overflow feature allows you to limit the size of the LSDB and to maintain a
consistent LSDB across all the routers in the domain, which ensures that all routers have a consistent
view of the network.
Consistency is achieved by:
• Limiting the number of external LSAs in the database of each router.
• Ensuring that all routers have identical LSAs.
To configure OSPF database overflow, use the following command:
config ospf ase-limit <number> {timeout <seconds>}
where:
Opaque LSAs
Opaque LSAs are a generic OSPF mechanism used to carry auxiliary information in the OSPF database.
Opaque LSAs are most commonly used to support OSPF traffic engineering.
Normally, support for opaque LSAs is auto-negotiated between OSPF neighbors. In the event that you
experience interoperability problems, you can disable opaque LSAs across the entire system using the
following command:
disable ospf capability opaque-lsa
To re-enable opaque LSAs across the entire system, use the following command:
enable ospf capability opaque-lsa
If your network uses opaque LSAs, we recommend that all routers on your OSPF network support
opaque LSAs. Routers that do not support opaque LSAs do not store or flood them. At minimum a
well-interconnected subsection of your OSPF network needs to support opaque LSAs to maintain
reliability of their transmission.
Areas
OSPF allows parts of a network to be grouped together into areas. The topology within an area is
hidden from the rest of the autonomous system. Hiding this information enables a significant reduction
in LSA traffic, and reduces the computations needed to maintain the LSDB. Routing within the area is
determined only by the topology of the area.
number Specifies the number of external LSAs (excluding the default LSAs)
that the system supports before it goes into overflow state. A limit
value of zero disables the functionality.
When the LSDB size limit is reached, OSPF database overflow
flushes LSAs from the LSDB. OSPF database overflow flushes the
same LSAs from all the routers, which maintains consistency.
timeout Specifies the timeout, in seconds, after which the system ceases to be
in overflow state. A timeout value of zero leaves the system in
overflow state until OSPF is disabled and re-enabled.