How big should an OSPF area be?
Generally, an area should have no more than 50 routers. Areas that suffer with unstable links should be smaller. Number of areas supported by any one router: A router must run the link-state algorithm for each link-state change that occurs for every area in which the router resides.
What is OSPF header?
The OSPF packet header contains the OSPF version and packet type, the router ID, area ID, and packet authentication and checksum information: Type.
What are the 7 stages of OSPF?
The states are Down, Attempt, Init, 2-Way, Exstart, Exchange, Loading, and Full.
What is the highest OSPF priority?
The OSPFv2 router assigned the highest priority becomes the designated router, and the OSPFv2 router with the second-highest priority becomes the backup router. If you set the priority to 0, the device does not participate in DR and BDR election.
What is Area 0 called in OSPF?
Backbone Area
Backbone Area This is the central area in your OSPF routing domain which all areas must connect to. This area is labeled area 0 (or the longhand version 0.0. 0.0). When traffic needs to pass from one area to another, it must traverse the backbone.
Why do we need AREA 0 in OSPF?
According to the OSPF design principle, area 0 plays the role of the central node in the OSPF network. The link information of other areas is transmitted through area 0. This also means that all other areas must be connected to area 0. This area supports 1, 2, 3, 4, and 5 LSAs.
What is Type 1 and Type 2 in OSPF?
A type 1 route has a metric that is the sum of the internal OSPF cost and the external redistributed cost. A type 2 route has a metric equal only to the redistributed cost, as shown in Figure 14-2.
What are the 5 types of OSPF packets?
Packet types for OSPF
- Hello 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 LSA in OSPF?
The link-state advertisement (LSA) is a basic communication means of the OSPF routing protocol for the Internet Protocol (IP). It communicates the router’s local routing topology to all other local routers in the same OSPF area.
Who is elected first DR or BDR?
If no router is a DR or a BDR on a given subnet, the BDR is first elected, and then a second election is held for the DR. What are the criteria for the DR election process? The DR is elected based on the following default criteria: If the priority setting on an OSPF router is set to 0, it can never become a DR or BDR.
What are OSPF LSA types?
OSPF LSA Types Explained
- LSA Type 1: Router LSA.
- LSA Type 2: Network LSA.
- LSA Type 3: Summary LSA.
- LSA Type 4: Summary ASBR LSA.
- LSA Type 5: Autonomous system external LSA.
- LSA Type 6: Multicast OSPF LSA.
- LSA Type 7: Not-so-stubby area LSA.
- LSA Type 8: External attribute LSA for BGP.
What are LSA types?
Let’s start with an overview:
- LSA Type 1: Router LSA.
- LSA Type 2: Network LSA.
- LSA Type 3: Summary LSA.
- LSA Type 4: Summary ASBR LSA.
- LSA Type 5: Autonomous system external LSA.
- LSA Type 6: Multicast OSPF LSA.
- LSA Type 7: Not-so-stubby area LSA.
- LSA Type 8: External attribute LSA for BGP.
Can we have OSPF without Area 0?
No. OSPF requires that there be an area 0 for routing between two different areas.
What is OSPF backbone area?
Backbone Areas
An OSPF backbone area consists of all networks in area ID 0.0. 0.0, their attached routing devices, and all ABRs. The backbone itself does not have any ABRs. The backbone distributes routing information between areas.
How many LSA are in OSPF?
6 Types of OSPF LSA.
What is E1 and E2 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 happens when Dr fails in OSPF?
If you lose a DR on a broadcast network, there is no communication between the rest of the routers until a new DR is elected, this can take afew minutes, if you dont have any BDR. By having a BDR already in place, this cuts down the protocols “lack of visability time”.
What is NSSA in OSPF?
The OSPF not-so-stubby area (NSSA) feature is described by RFC 1587. and is first introduced in Cisco IOS® Software release 11.2. It is a non-proprietary extension of the existing stub area feature that allows the injection of external routes in a limited fashion into the stub area.
Is Area 0 required 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.
What is LSP and LSA?
What is an LSA and LSP? An LSA is a Learning Support Assistant and an LSP is Learning Support Practitioner. This is somebody who supports learning in the classroom. Sometimes they will support individual children, at other times they may work with a group or with the whole class.
What is N1 and N2 in OSPF?
E1 or E2 or N1 or N2 type routes are based upon cost of the route. E2 or N2 routes tell OSPF routers to set the metric as the metric at the point of redistribution.(At the ASBR) E1 or N1 routes tell OSPF routers to add the internal costs to reach the ASBR to the cost set at the point of redistrbution (At the ASBR)
Who elected first DR or BDR in OSPF?
Keep in mind that a given OSPF speaker in your network can have some interfaces that are designated and others that are backup designated, and others that are non-designated. If no router is a DR or a BDR on a given subnet, the BDR is first elected, and then a second election is held for the DR.
What is Type 7 LSA OSPF?
What Is a Type 7 LSA? This is a type 7 LSA that is generated by an NSSA ASBR. Type 5 LSAs are not allowed in NSSA areas, so the NSSA ASBR generates a type 7 LSA instead, which remains within the NSSA. This type 7 LSA gets translated back into a type 5 by the NSSA ABR.
Which route is preferred E1 or E2?
You can have ASBR 1 inject the external route as E1 and ASBR 2 inject the same external prefix as an E2 route. Due to the order of operations of OSPF, the E1 route will always be preferred regardless of the cost to the ASBR. But in case of single point of redistribution, it doesn’t matter what route type you use.
What is E1 E2 and N1/N2 routes in OSPF?
A route redistributed (from a connected, static or other routing protocol) inside an NSSA area is a Type 7 LSA or N route. This LSA is circulated only within the NSSA area. E1 or E2 or N1 or N2 type routes are based upon cost of the route. Consider this example.