OSPF Stub Area basically filters out information of an OSPF database purely based on the LSA types
Link-state advertisement
The link-state advertisement is a basic communication means of the OSPF routing protocol for the Internet Protocol. It communicates the router's local routing topology to all other local routers in the same OSPF area. OSPF is designed for scalability, so some LSAs are not flooded out on all interfaces, but only on those that belong to the appropriate area. In this way detailed information can be kept localiz…
What are OSPF stubs?
OSPF stubs allow the OSPF routers in an area to use default routes for forwarding packets to Area Border Routers (ABRs), rather than more specific routes. OSPF stubs reduce memory consumption and CPU processing time on the routers inside the area because the routers in that area can have fewer LSAs in their LSDBs...
What is default route in OSPF stub?
Default routes are advertised into stub area by the ABR. All OSPF routers in stub area must be configured as stub. In short: OSPF stub allow the routers in an area to use default route for forwarding packets to ABR rather than more specific routes.
What is the use of stub area area?
Stub Area area allow the routers in an area to use default routes for forwarding packets to ABR (Area Border Router). Using these default routes in an area reduces memory & CPU consumption due to reduced number of LSAs in LSDBs.
What is totally stubs in Cisco NSSA?
Totally stubs is reduces the routing table to a minimum. This is a Cisco proprietary feature. NSSA breaks stub area rules. NSSA area creates a special type of link-state advertisement (LSA) known as type 7, type 7 LSAs is only exist in NSSA area.
What is the use of stub area?
Stub area, also called stub area, the so-called stub area, means that the area does not accept any external routes of non-OSPF network, if it wants to reach those external routes, only Need to send it through the default route. This area supports 1, 2, and 3 LSAs.
What is stub zone in OSPF?
Stub areas are areas through which or into which OSPF does not flood AS external link-state advertisements (Type 5 LSAs).
What is a stub area?
A stub area is an area in which advertisements of external routes are not allowed, reducing the size of the database. A totally stubby area (TSA) is a stub area in which summary link-state advertisement (type 3 LSAs) are not sent.
What is the difference between backbone area and stub area in OSPF?
The backbone is considered a standard area. Stub areas can contain type 1, 2, and 3 LSAs. A default route is substituted for external routes. Totally stubby areas can only contain type 1 and 2 LSAs, and a single type 3 LSA.
What is the difference between stub area and NSSA?
Difference between NSSA/Totally NSSA and Stubby/Totally Areas is; NSSAs redistribute external routes(Type-7 LSA) into the Area., Stubbys don't. NSSA was created because Stubby areas block all Type-5 external LSAs. So Stubby Area can not learn any external LSAs. NSSA lets stub area to learn external Areas(Type-7 LSAs).
Why do we need AREA 0 in OSPF?
An OSPF routing domain (AS) can consist of a single area, but in that case the single area must be Area 0. Only the backbone area can generate the summary routing topology information that is used by the other areas. This is why all interarea traffic must pass through the backbone area.
How do I set up a stub area?
Stub Areas accept the summary LSAs Type 3 beside the Default Route from the Backbone Area. They also do not accept Type 4 LSAs. To configure an area as a Stub Area, we need to configure all the routers in this area as Stub. Because, configuring a router interface as a Stub, changes the option bits in the Hello Packets.
What is OSPF stub no summary?
when you define a stub area, you still receive all routes from other areas, including IA routes. The stub area creates a default route for external routes only, that is, routes redistributed into OSPF from another protocol. By adding 'no-summary', you create a so-called totally stubby area.
What is the difference between E1 and E2 routes in OSPF?
E1 routes indicate cumulative cost to reach the destination i.e. int indicates cost to reach ASBR + cost to destination from ASBR. E2 route reflects cost only from the ASBR to destination. This is the default used by ospf for redistribution.
What is OSPF super backbone area?
The super- backbone appears as another area to the CE-routers. s. Routes redistributed into MP-BGP from OSPF will appear as inter-area routes in other OSPF sites if the original route was an intra-area or inter-area route and as external routes if the original route was an external route.
Can we use OSPF without backbone area?
No. OSPF requires that there be an area 0 for routing between two different areas.
What are the 7 stages of OSPF?
The states are Down, Attempt, Init, 2-Way, Exstart, Exchange, Loading, and Full.
What is Area 0 called in OSPF?
The backbone area (also known as area 0 or area 0.0. 0.0) forms the core of OSPF networks. All other areas should be connected to the backbone area either by a direct link or by virtual link configuration.
What are the 5 types of OSPF packets?
Packet types for OSPFHello packet. This packet is sent by the OMPROUTED server to discover OSPF neighbor routers and to establish bidirectional communications with them. ... Database description packet. ... Link-state update packet. ... Link-state request packet. ... Link-state acknowledgment packet.
What is Type 7 LSA OSPF?
Type 7 – External LSA: also known as not-so-stubby-area (NSSA) LSA: As you can see area 2 is a NSSA (not-so-stubby-area) which doesn't allow external LSAs (type 5).
What is E2 route in OSPF?
OSPF External Routes (E2) are advertised into OSPF Autonomous System with a particular cost and the cost is not changed throughout the AS. The routes are learned via redistribution of other routing protocol or static route or a connected subnet.
What is meant by stub network?
A stub network, or pocket network, is a somewhat casual term describing a computer network, or part of an internetwork, with no knowledge of other networks, that will typically send much or all of its non-local traffic out via a single path, with the network aware only of a default route to non-local destinations.
What is stub router?
Stub routers in EIGRP, are nodes that are designed to be only directly connected to networks and are not designed to be in transit for the data plane. Meaning, EIGRP stub routers are designed for very small branch office routers or for edges of the network.
What are the 5 types of OSPF packets?
Packet types for OSPFHello packet. This packet is sent by the OMPROUTED server to discover OSPF neighbor routers and to establish bidirectional communications with them. ... Database description packet. ... Link-state update packet. ... Link-state request packet. ... Link-state acknowledgment packet.
What is OSPF super backbone area?
The super- backbone appears as another area to the CE-routers. s. Routes redistributed into MP-BGP from OSPF will appear as inter-area routes in other OSPF sites if the original route was an intra-area or inter-area route and as external routes if the original route was an external route.
What happens if you configure an area as stub?
If you configure an area as stub it will block all type 5 external LSAs. All the prefixes that you redistributed into OSPF from another routing protocol are not welcome in the stub area. Since you are not allowed to have type 5 external LSAs in the stub area it’s also impossible to have an ASBR in the stub area. In order to reach networks in other areas there will be a default route.
Can you have an ASBR in a totally stub area?
It’s impossible to have an ASBR in the totally stub area since type 5 external LSAs are blocked. If you want to block type 3 summary LSAs and type 5 external LSAs but still need an ASBR within the totally stub area you can turn it into a totally NSSA (totally not-so-stubby-area).
Can you use NSSA as a stubby area?
Of course there’s always an exception. So what if you want an area to be stub area but you also have an ASBR in this area? You can use the NSSA (not-so-stubby-area). This is the same thing as the stub area with the exception that you are allowed to have an ASBR within the area. How does it work? This is where the type 7 external LSA kicks in. Since we are not allowed to use the type 5 external LSA we’ll just use a new LSA type.
What Are Areas, Stub Areas, and Not-So-Stubby Areas?
An OSPF network can be divided into sub-domains called areas. An area is a logic al collection of OSPF networks, routers, and links that have the same area identification. A router within an area must maintain a topological database for the area to which it belongs. The router does not have detailed information about network topology outside of its area, which thereby reduces the size of its database.
What is an area 7 stub?
The routers in area 7 must send a packet to the ABR to reach the ASBR, no matter what the external destination. Area 7 can be defined as a stub area. In order to define area 7 as a stub area, configure the area 7 stub command in all routers in that area.
What is a totally stubby area?
Not-so-stubby areas (NSSAs) are an extension of OSPF stub areas. Like stub areas, they prevent the flooding of AS-external link-state advertisements ...
What is an area border router?
An area border router is in the OSPF boundary between two areas. Both sides of any link always belong to the same OSPF area. An autonomous system boundary router (ASBR) advertises external destinations throughout the OSPF autonomous system. External routes are the routes redistributed into OSPF from any other protocol.
What is the benefit of creating an area?
The main benefit of creating areas is a reduction in the number of routes to propagate - by the filtering and the summarization of routes. Each OSPF network that is divided into different areas must follow these rules: A backbone area - which combines a set of independent areas into a single domain - must exist.
What is a Type 7 LSA?
Type-7 LSAs are similar to Type-5 AS- external LSAs, except that they can only be flooded into the NSSA. In order to further propagate the NSSA external information, the Type-7 LSA must be translated to a Type-5 AS-external-LSA by the NSSA ABR. NSSA is supported in Cisco IOS 11.2 and later.
Where are NSSAs placed?
As a result, NSSAs (like stub areas) must be placed at the edge of an OSPF routing domain. NSSAs are more flexible than stub areas in that an NSSA can import external routes into the OSPF routing domain and thereby provide transit service to small routing domains that are not part of the OSPF routing domain.
What is Time-based access-list? How to configure Time-based access-list?
Time-based access-list is type of access-list which allows network access on the basis of given time period. It is useful when you want to p...
What is a stub area?
Stub area is isolated area that does not receive External LSA. Routers in Stub areas do not receive type 4 and type 5 LSAs it is replaced by a default route to external autonomous system advertised by the area border router (ABR) Stub area can have type 1, 2, and 3 OSPF LSAs.
Why do OSPF stubs work?
OSPF stubs allow the OSPF routers in an area to use default routes for forwarding packets to Area Border Routers (ABRs), rather than more specific routes. OSPF stubs reduce memory consumption and CPU processing time on the routers inside the area because the routers in that area can have fewer LSAs in their LSDBs.
