OSPF EXAM QUESTIONS AND ANSWERS 2024 SOLVED 100%

adjacencies formula - For any number of routers (designated as n) on a multiaccess network, there are n (n - 1) / 2 adjacencies. adjust interface bandwidth - #int s0/0/0 #bandwidth [kb] Advertising and enabling OSPF - V2: (config)# router ospf [process-id] # network [network ip] [wildcard mask] area {0} # passive-interface {g0/0} # default-information originate (used with default route) # auto-cost reference-bandwidth [Mb] V3: (conofig)# ipv6 router ospf [process-id] #passive-interface {g0/0} #auto-cost reference-bandwidth [Mb] # default-information originate (used with default route ) #int s0/0/0 #ipv6 ospf {1} area {0} #int g0/0 #ipv6 ospf {1} area {0} command to restart the ospf process - #clear ip(v6) ospf processHello packet fields - Type - Identifies the type of packet. A one (1) indicates a Hello packet. A value 2 identifies a DBD packet, 3 an LSR packet, 4 an LSU packet, and 5 an LSAck packet. Router ID - A 32-bit value expressed in dotted decimal notation (an IPv4 address) used to uniquely identifying the originating router. Area ID - Area from which the packet originated. Network Mask - Subnet mask associated with the sending interface. Hello Interval - Specifies the frequency, in seconds, at which a router sends Hello packets. The default Hello interval on multiaccess networks is 10 seconds. This timer must be the same on neighboring routers; otherwise, an adjacency is not established. Router Priority - Used in a DR/BDR election. The default priority for all OSPF routers is 1, but can be manually altered from 0 to 255. The higher the value, the more likely the router becomes the DR on the link. Dead Interval - Is the time in seconds that a router waits to hear from a neighbor before declaring the neighboring router out of service. By default, the router Dead Interval is four times the Hello interval. This timer must be the same on neighboring routers; otherwise, an adjacency is not established. Designated Router (DR) - Router ID of the DR. Backup Designated Router (BDR) - Router ID of the BDR. List of Neighbors - List that identifies the router IDs of all adjacent routers. Hello packet intervals - OSPF Hello packets are transmitted to multicast address 224.0.0.5 in IPv4 and FF02::5 in IPv6 (all OSPF routers) every: 10 seconds (default on multiaccess and point-to-point networks)30 seconds (default on nonbroadcast multiaccess [NBMA] networks; for example, Frame Relay) Dead Interval: Cisco uses a default of 4 times the Hello interval: 40 seconds (default on multiaccess and point-to-point networks) 120 seconds (default on NBMA networks; for example, Frame Relay) Hello packets are used to: - Discover OSPF neighbors and establish neighbor adjacencies. Advertise parameters on which two routers must agree to become neighbors. Elect the Designated Router (DR) and Backup Designated Router (BDR) on multiaccess networks like Ethernet and Frame Relay. Point-to-point links do not require DR or BDR. LSUs - Routers initially exchange Type 2 DBD packets, which is an abbreviated list of the sending router's LSDB and is used by receiving routers to check against the local LSDB. A Type 3 LSR packet is used by the receiving routers to request more information about an entry in the DBD. The Type 4 LSU packet is used to reply to an LSR packet. LSUs are also used to forward OSPF routing updates, such as link changes. Specifically, an LSU packet can contain 11 different types of OSPFv2 LSAs, as shown in the figure. OSPFv3 renamed several of these LSAs and also contains two additional LSAs. LSA types: 1: Router LSAs 2: Network LSAs3 or 4: Summary LSAs 5: Autonomous System External LSAs 6: Multicast OSPF LSAs 7: Defined for Not-So-Stubby areas 8: External Attributes LSA for BGP 9, 10, 11: Opaque LSAs multiarea OSPF - All areas must connect to the backbone area (area 0). Routers interconnecting the areas are referred to as Area Border Routers (ABR).