Area Types -Standard area -Backbone area (area 0) -Stub area -Totally stubby area -Not-so-stubby area (NSSA) -Totally NSSA Stub Area (area stub) -It contain type 1, 2, and 3 LSAs -No LSA type 4 and 5 (E1 or E2) is allowed -Routers can connect to the External routes via the default route that is injected [...]
Yes, OSPF can authenticate all packets exchanged between neighbors. Authentication may be through simple passwords or through MD5 cryptographic checksums. To configure simple password authentication for an area, use the command ip ospf authentication-key to assign a password of up to eight octets to each interface attached to the area. Then, issue the area x [...]
What command displays a summary list of OSPF interfaces that includes a column for the cost of each interface?
R1#show ip ospf interface brief
When Open Shortest Path First (OSPF) is enabled on a router or when a router configured for OSPF is powered up, it tries to discover its OSPF neighbors and synchronize its database with them. Routers are said to be OSPF neighbors when they see their router ID in the received hello packet and the status [...]
With which network type will OSPF establish router adjacencies but not perform the DR/BDR election process?
A- Point-to-point B- Backbone area 0 C- Broadcast multi-access D- Non-broadcast multi-access Answer is:A
The Open Shortest Path First (OSPF) neighbors are established by exchanging hello packets at multicast address 126.96.36.199. If these packets fail due to any Layer 2 (L2) issue, OSPF neighbors flap. This results in the error message ‘OSPF-5-ADJCHG’ To resolve this issue, ensure that the underlying L2 between OSPF neighbors is working properly by issuing [...]
Configuring distribute-list commands that utilize route maps will not achieve desired Link State Advertisement (LSA) filtering. Open Shortest Path First Protocol (OSPF) routes cannot be filtered from entering the OSPF database using distribute-list. The distribute-list in command only filters routes from entering the routing table, and it does not prevent LSA packets from being propagated. [...]
In router you can choose to manually set the ‘passive-interface’ command on the interfaces where adjacency is not desired. The interface address that you specify as passive appears as a stub network in the OSPF domain. OSPF routing information is neither sent nor received through the specified device interface. Passive interface can be configured in [...]
There are two ways of authentication in OSPF. 1) Clear text authentication 2) MD5 authentication 1) Clear text authentication Area based authentication Cisco_Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Cisco_Router(config)#interface f0/0 Cisco_Router(config-if)#ip ospf authentication-key cisco@123 Cisco_Router(config-if)#exit Cisco_Router(config)#router ospf 100 Cisco_Router(config-router)#area 2 authentication Cisco_Router(config-router)#exit Interface based authentication Cisco_Router(config)#int fa0/0 Cisco_Router(config-if)#ip ospf authentication [...]
OSPF routers on multiaccess segments sync their databases with their Designated Router (DR) or a Backup Designated Router (BDR) only. The OSPF status between two routers transitions to Full only if at least one of them is a DR or a BDR. The state remains Two-way between a pair of routers if both routers are drothers.
The Neighborship will be formed but it will not form FULL Adjecency. DBD exchange might not happen and the neighborship will be stuck in “EXSTART / EXCHANGE” state. You can configure OSPF to ignore MTU checking by issuing “ip ospf mtu-ignore” on any one side.
Think about a case where you have 4 routers with a LAN, A, B, C and D. A will be the DR and B will be the BDR. In such in a situation, router C’s neighbor state per neighbor will be as follows: A – Full B – Full D — TwoWay Each non-DR/non-BDR router [...]
OSPF allows for two forms of summarization. -One form of summarization is used when summarizing routes redistributed in to OSPF from another routing protocol. -The other form of summarization is used when summarizing an area. With both forms of summarization, summary LSAs are created and flooded toward Location 0, or the central source area. The [...]
States in OSPF neighbor adjacency process: -Down State -Attempt -Init -2-way -Exstart -Exchange -Loading -Full Down: This is the first OSPF neighbor state. It indicates that no Hello has been received from the neighbor. Attempt: This state is only valid for manually configured neighbors in an NBMA environment. Init: This state indicates that the router [...]
The Type 3 (Summary) LSA is originated by Area Border Routers into one area to describe links in another area. The Type 4 (ASBR Summary) LSA is also originated by an ABR, but it is used to describe an ASBR in one area to routers in another area.
OSPF collect information from all router on the network than OSPF store all this information in a database and use that information to build a topology map. This information will allow OSPF to identify the best or shortest route to every other network segment on the network. The route selection is based on overall hops [...]
Broadcast Default on broadcast medias (Ethernet / Token Ring) Sends hellos as multicast Performs DR/BDR Election Non-Broadcast Default on multipoint NBMA medias (Frame Relay / ATM) Sends hellos as unicast (“neighbor” command) Performs DR/BDR Election Point-to-Point Default on point-to-point medias (HDLC / PPP) Sends hellos as multicast No DR/BDR Election Only two neighbors on the [...]
If you have the two routers in the same area, can you use the distribute-list out command to filter resources between them
No to filter the routes use the command distribute-list in command not the distribute-list out. To filter networks received in updates, use the distribute-list in command in address family or router configuration mode. To change or cancel the filter, use the no form of this command. distribute-list [access-list-number | name] | [route-map map-tag] in [interface-type [...]
External routes fall under two categories, external type 1 and external type 2. The difference between the two is in the way the cost (metric) of the route is being calculated. The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route. A type 1 [...]
The DR serves as a common point for all adjacencies on a multiaccess segment The BDR also maintains adjacencies with all routers in case the DR fails Area Border Router (ABR) Connects two or more areas AS Boundary Router (ASBR) Connects to additional routing domains; typically located in the backbone
OSPF relies on several types of Link State Advertisements (LSAs) to communicate link state information between neighbors.
OSPF relies on several types of Link State Advertisements (LSAs) to communicate link state information between neighbors. A brief review of the most applicable LSA types: Type 1 – Represents a router Type 2 – Represents the pseudonode (designated router) for a multiaccess link Type 3 – A network link summary (internal route) Type 4 – Represents an ASBR Type 5 – [...]
Hello-Used to discover and maintain neighbours. Database Description-Used to form adjacencies. The router summarises all its linkstate advertisements and passes this information, via database description packets to the router it is forming an adjacency with Link State Request After the database description packets have been exchanged with a neighbour, the router may detect link state advertisements it requires to update [...]
Internal Router – all interfaces in single area Backbone Router – at least 1 interface in area 0 Area Border Router – has interfaces in multiple areas Autonomous System Border Router – act as gateways between OSPF and other routing protocols
OSPF allows the grouping of networks into a set, called an area. The topology of an area is hidden from the rest of the Autonomous System. This technique minimizes the routing traffic required for the protocol. When multiple areas are used, each area has its own copy of the topological database.
OSPF Tables: In link state routing protocol there are different tables for storing different types of information regarding router and its networks. There are three tables in OSPF same like in EIGRP. 1. OSPF Neighbor table 2. OSPF Topology table 3. OSPF Routing table