Part 6

distance vector

Both versions of RIP uses link-state or distance vector logic?

100 Mbps The reference bandwidth is a value in Mbps that you can set for yourself. However, the default is 100 Mbps on most Cisco routers

Default reference bandwidth for the OSPF algorithm for most Cisco routers?

Neither completely. Characterized either as advanced distance vector or a balanced hybrid

EIGRP uses link-state or distance vector logic?

-OSPF

Which one uses link-state logic? -EIGRP -OSPF -RIPv1 -RIPv2

**READ If you accidentally configure one OSPF router with a network type as broadcast and the other router with a network type point-to-point: -Both routers will exchange their LSDB. -Both routers will reach full state. -Neither router will add IP routes to the routing tables.

**READ If you accidentally configure one OSPF router with a network type as broadcast and the other router with a network type point-to-point: -Both routers will exchange their LSDB. -Both routers will reach full state. -Neither router will add IP routes to the routing tables.

**READ LSA Types

**READ LSA Types

**READ LSR (Link-State Request) = Used by a router to request specific LSAs from a neighbor LSU (Link-State Update) = Used by a router to send LSAs to a neighbor DD (Link-State Database Descriptor) = Used by a router to send a summary list of LSAs to a neighbor, as part of the process of a router deciding which LSAs it should request with LSR packets

**READ LSR (Link-State Request) = Used by a router to request specific LSAs from a neighbor LSU (Link-State Update) = Used by a router to send LSAs to a neighbor DD (Link-State Database Descriptor) = Used by a router to send a summary list of LSAs to a neighbor, as part of the process of a router deciding which LSAs it should request with LSR packets

**READ Neighbor Requirements for OSPF

**READ Neighbor Requirements for OSPF

**READ The selection order for the 32-bit OSPFv2 RID, in order of priority: 1) Configured RID 2) Highest IPv4 address on a working loopback interface 3) Highest IPv4 address on any other working interface

**READ The selection order for the 32-bit OSPFv2 RID, in order of priority: 1) Configured RID 2) Highest IPv4 address on a working loopback interface 3) Highest IPv4 address on any other working interface

100 Although the RFC does not specify how cost is determined, Cisco defaults to a value that is inversely proportional to 100 Mbps. Because 100 Mbps / 1 Mbps = 100, the cost of this link would be 100.

A command reveals a router interface with a bandwidth of 1 Mbps. If not set using additional configuration, what cost will OSPF assign to the interface?

-It allows for simpler planning and operations The correct answer is the one advantage of using a single-area design. The three wrong answers are advantages of using a multiarea design, with all reasons being much more important with a larger internetwork.

A company has a small/medium-sized network with 15 routers and 40 subnets and uses OSPFv2. Which of the following is considered an advantage of using a single-area design as opposed to a multiarea design? -It reduces the processing overhead on most routers -It allows for route summarization, reducing the size of IP routing tables -Status changes to one link may not require SPF to run on all other routers -It allows for simpler planning and operations

-MTU -network type

For Neighbor Requirements for OSPF, 2 routers would still be neighbors if either of these two settings are incorrect. (They just wouldn't be able to exchange LSDBs.) -Neighboring interfaces must use same ______ setting -Neighboring interfaces must use same _________ type

-R4, router-id 4.4.4.4, priority 1 First, the DR election always chooses the BDR to become the DR if a BDR exists. However, the question states that all the routers just rebooted, so there should be no BDR to take over for the DR. As worded, the question creates a scenario where all routers compete equally to become the DR. The routers choose the router with the highest OSPF interface priority, and if a tie, they can use the router with the highest RID. In this case, the answers show routers with different priorities, so no ties exist based on priority. As a result, R1, with the highest priority (4), becomes the DR.

Four OSPF routers connect to the same LAN. In a new election after all routers have been rebooted, which router wins the DR election? -R3, router-id 3.3.3.3, priority 2 -R4, router-id 4.4.4.4, priority 1 -R1, router-id 1.1.1.1, priority 4 -R2, router-id 2.2.2.2, priority 3

Priority You can change the priority of an OSPF router interface to influence the DR election. The other option is to change the RID because the one with the highest RID will be elected as DR. The network type can decide if OSPF will use a DR/BDR, but it will not influence an election. The timers don't influence the election, but all timers need to be identical on all routers participating in the OSPF process.

How can you configure on an OSPF router interface to influence the DR election? -Network type -Cost -Timers -Priority

-Use of the IP address of the active loopback interface with the highest IP address

If not configured with the router-id command, what is the next option a Cisco router uses to choose its OSPF RID?

-An ACL could be blocking router advertisements. -Any physical layer problem that would prevent two neighboring routers from being able to ping each other's IPv4 addresses in the subnet that exist between the two routers. Right answers --> - ACLs cold block OSPF messages, which would prevent neighbors from forming adjacencies and therefore prevent the advertisements from being sent from an OSPF router. -OSPFv2 requires the ability to send IPv4 packets between neighboring routers for those routers to exchange OSPF routing information. Wrong answers --> -Neighboring OSPF routers must match in regards to OSPF area, subnet, and IPv4 subnet mak. -Neighboring OSPF routers may use different OSPF process IDs or the same OSPF process ID, and still become neighbors.

Imagine you configured OSPFv2 in a small lab network. Which lists a reason why the routers in your lab would not learn all the routes to all the IPv4 subnets (or networks) in your small lab network? (CHOOSE 2) -Two neighboring routers that connect to the same link have been configured with the same OSPF area and with the same IPv4 mask. -An ACL could be blocking router advertisements. -Any physical layer problem that would prevent two neighboring routers from being able to ping each other's IPv4 addresses in the subnet that exist between the two routers. -Two neighboring routers that connect to the same link have been configured with the same OSPF process ID on the router ospf command

-The router ID is configured explicitly in router mode -An interface's area number is configured in interface mode The configuration enables OSPF and identifies the area number to use with the interface using an interface subcommand in interface mode: the ip ospf [process-id] area [area-number] command. However, to explicitly configure the RID, the configuration must use the router-id [RID value] command, which is a command issued in OSPF router mode.

OSPF interface configuration uses the ip ospf [process-id] area [area-number] configuration command. In which modes do you configure the following settings when using this command? (CHOOSE 2) -The router ID is configured explicitly in interface mode -The router ID is configured explicitly in router mode -An interface's area number is configured in router mode -An interface's area number is configured in interface mode

-Mismatched Hello intervals -Mismatched subnet numbers Wrong answers --> -The dead intervals must match for the routers to become neighbors, and the dead interval defaults to 4x the Hello interval, but the dead interval does not have to be 4x the Hello interval. -The network commands on the two routers do not have to match in anyway at all; the only requirement is that both routers have OSPF enabled on the interfaces somehow. -OSPF uses interface IP addresses and multicast addresses as the source and destination of OSPF packets, often which do not happen to be the OSPF RID, so an ACL that matches the RID would not necessarily stop OSPF from working.

OSPF routers can hear Hellos from another router, but not FORM neighbor relationships. Which of the following definitely prevent neighbor relationships from being formed? -An ospf access-group 101 in command on the interface, with ACL 101 filtering the RID of the other router -Mismatched Hello intervals -Mismatched subnet numbers -Mismatched networks listed in the configured network commands -When both routers have the same configured dead interval, but with the dead interval not being 4x the Hello interval

225.0.0.5 EIGRP routers use 224.0.0.10. RIP routers use 224.0.0.9 DHCP server/relay agents use 224.0.0.12

OSPF-enabled routers send Hello packets using which multicast IP address?

-eBGP In situations where multiple routes exist to the same destination/mask from multiple sources, a tie-breaking mechanism must exist. On Cisco devices, the tie-breaking mechanism is AD. Of the available options, eBGP has an AD of 20, EIGRP AD of 90, OSPF AD of 110, and RIP AD of 120. The source with the lower value is preferred over the others, giving the route sourced from eBGP with the priority.

One router learns multiple different routes, with multiple routing protocols, for the exact same destination IPv4 subnet/mask. The answers list all the routing protocols used; which answer lists the routing protocol who route would be chosen as best and added to the IPv4 routing table? -RIP -EIGRP -OSPF -eBGP

-R15 keeps all OSPF configuration but ceases all OSPF activities (routes, LSDB, neighbors) The OSPF shutdown command tells the OSPF process to stop operating. That process includes removing any OSPF-learned routes from the IP routing table, clearing the router's LSDB, and closing existing OSPF neighbor relationships. In effect, it causes OSPF to stop working on the router, but it does retain the configuration so that a no shutdown command will cause the router to start using OSPF again with no changes to the configuration.

Router R15 has been a working part of a network that uses OSPFv2. An engineer then issues the shutdown command in OSPF configuration mode on R15. Which occurs? -R15 empties its LSDB but keeps OSPF neighbor relationships active. -R15 keeps all OSPF configuration but ceases all OSPF activities (routes, LSDB, neighbors) -R15 empties its IP routing table of all OSPF routes but keeps its LSDB intact -R15 keeps OSPF neighbors open but does not accept new OSPF neighbors

-R1's show ip ospf neighbor command will list R2 and a state of "FULL/DR" -R1 will dynamically discover the existence of R2 By default, IOS assigns Ethernet interfaces an OSPF network type of broadcast, with an OSPF interface priority of 1. As a result, both routers attempt to discover the other routers on the link (which identifies one correct answer.) The broadcast network type means that the routers also attempt to elect a DR and BDR. With a tie-in priority, the routers choose the DR based on the highest RID values, meaning R2 will become the DR and R1 will become the BDR. These facts combine to show why the two incorrect answers are incorrect. The other correct answer is correct because the show ip ospf neighbor command lists the local router's neighbor relationship state (FULL) and the role filled by that neighbor (DR), which will be the output show on R1 when R2 is acting as DR.

Routers R1 and R2, with RIDs 1.1.1.1 and 2.2.2.2, connect over an Ethernet WAN link. If using all default OSPF settings, if the WAN link initializes for both routers at the same time, which of the following answers are true? (CHOOSE 2) -R1's show ip ospf neighbor command will list R2 and a state of "FULL/DR" -R1 will dynamically discover the existence of R2 -R1 will become the DR -R2 will be neither the DR nor the BDR

-R1 will dynamically discover the existence of R2 -R2 will be neither the DR nor the BDR First, the OSPF point-to-point network type causes the two routers to dynamically discover neighbors, making one answer correct. Next, IOS assigns a default OSPF interface priority of 1, so R1's configured priority of 11 would be better in a DR/BDR election. However, the point-to-point network type causes the router to not use a DR/BDR on the interface. As a result, the answer about R1 becoming the DR is incorrect (because no DR exists at all), and the answer listing a state of "FULL/DR" is incorrect for the same reason. However, the answer that claims that R2 will be neither DR nor BDR is true because no DR or BDR is elected.

Routers R1 and R2, with RIDs 1.1.1.1 and 2.2.2.2, connect over an Ethernet WAN link. The configuration uses all defaults, except giving R1 an interface priority of 11 and changing both routers to use OSPF network type point-to-point. If the WAN link initializes for both routers at the same time, which of the following answers are true? (CHOOSE 2) -R1 will dynamically discover the existence of R2 -R2 's show ip ospf neighbor command will list R1 with a state of "FULL/DR" -R2 will be neither the DR nor the BDR -R1 will become the DR

-Type 2 Every router creates a Type 1 LSA for itself, describing that router and its interfaces. A different does exist with Type 2 LSAs. Type 2 LSAs are network LSAs, created by the designated router in the subnet, which describe the subnet to which multiple routers connect. R1 will create and flood a Type 2 LSA for the subnet, but R2 as BDR, will not. The two routers are internal routers, that is, they have interfaces in one area only, and are not ABRs. Type 3 LSAs are summary LSAs, created by the ABR, describing to one area a subnet that exists in a different area. So neither R1 nor R2 will create any Type 3 LSAs.

Two internal OSPF routers connect to the same LAN-based subnet, with R1 acting as DR and R2 as BDR. What LSA will R1 create and flood that R2 does not? -There is no difference in the type of LSAs each router creates and floods. -Type 1 -Type 2 -Type 3

-Run some SPF math against the LSAs to calculate the routes. LSAs contain topology information that is useful in calculating routes, but the LSAs do not directly list the route that a router should add to its routing table. In this case, R1 would run a calculation called the SPF algorithm (Shortest Path First), against the LSAs, to determine what IP routes to add to the IP routing table.

Two routers using OSPFv2 have become neighbors and exchanged all LSAs. As a result, Router R1 now lists some OSPF-learned routes in its routing table. Which best describes how R1 uses those recently learned LSAs to choose which IP routes to add to its IP routing table? -Some LSAs list a route that can be copied to the routing table. -Each LSA lists a route to be copied to the routing table. -Run some SPF math against the LSAs to calculate the routes. -R1 does not use the LSAs at all when choosing what routes to ad.

-Hello 10, Dead 40 Also, the dead timers should always be 4x the Hello timer

What are the default timers for an OSPF point-to-point network type? -Hello 10, Dead 30 -Hello 30, Dead 120 -Hello 10, Dead 40 -Hello 30, Dead 90

-OSPF RID -OSPF interface priority The highest interface priority value wins during an election. Those values range from 0-255. The sequence works like this: 1) During an election, the routers choose the router with the highest interface priority. 2)If the interface priority ties, the election chooses the router with the highest OSPF RID. The other two settings (reference bandwidth and process ID) have no impact on the DR/BDR election.

What are two configurable settings that can influence the DR/BDR election? -OSPF reference bandwidth -OSPF RID -OSPF process ID -OSPF interface priority

-Each router sees its RID in the hello packet sent by the neighboring router -The routers exchanged Hellos and all necessary parameters match -The routers are neighbors and are read to exchange their LSDBs A two-way state will be reached after several steps. The routers will both send Hellos, check parameters, and if the parameters match, list the neighbor's RID in subsequent Hellos. At that point, both reach a 2-way state and are ready to exchange their LSDBs. Note that OSPF does not use ping as any part of establishing a neighbor relationship. Also, note that if the routers had begun to exchange their LSDBs, they would have reached other OSPF neighbor states.

What is true when two OSPF routers both reach the two-way state of their neighbor relationship? (CHOOSE 3) -Each router sees its RID in the hello packet sent by the neighboring router -The routers exchanged Hellos and all necessary parameters match -The routers exchanged their LSDBs -The routers are neighbors and are read to exchange their LSDBs -The routers succeeded in pinging each other

-The will fail to exchange their LSDBs If two OSPF routers have different MTU sizes, they can still form a neighbor relationship, but they will NOT be able to exchange their LSDBs; therefore, they won't exchange routes. After a certain time, the neighbor relationship will fail also. The routers will not be able to exchange routes. MTU sizes will not change the hello/dead timers or the RIDs.

What will happen if two OSPF routers have different MTU sizes? -They will have duplicate RIDs -The hello/dead timers will change -The will fail to exchange their LSDBs

-Type 1 and 2

Which LSA types describe topology inside an OSPF area? -Type 1 and 2 -Type 2 and 3 -Type 1 and 3

-LSU The OSPF LSU is used to send requested LSAs between neighbors; the LSR is used to request those LSAs that are specific missing from a router's LSDB. The DD is used to exchange a list of known LSAs between neighbors; it is from this list that a router learns which LSAs it does not know.

Which OSPF message type is used to actually send the LSAs between neighbors? -LSR -DD -LSU

-Full

Which OSPF neighbor state is expected when the exchange of topology information is complete between two OSPF neighbors? -2-way -Final -Full -Up/up

-The routers would use a LSR packet to ask for missing LSAs -The routers would use a LSU packet to send full LSAs to other routers LSR (Link-State Request) = Used by a router to request specific LSAs from a neighbor LSU (Link-State Update) = Used by a router to send LSAs to a neighbor DD (Link-State Database Descriptor) = Used by a router to send a summary list of LSAs to a neighbor, as part of the process of a router deciding which LSAs it should request with LSR packets

Which answers correctly describe the function of OSPF messages during the database exchange process? (CHOOSE 2) -The routers would use a LSR packet to ask for missing LSAs -The routers would use a DD packet to ask for missing LSAs -The routers would use a LSU packet to send full LSAs to other routers -The routers would use a DD packet to send full LSAs to other routers -The routers would use a LSU packet to ask for missing LSAs

-OSPF -EIGRP -RIPv2

Which of the following IGP routing protocols support VLSM? (CHOOSE 3) -OSPF -EIGRP -RIPv2 -RIPv1

delay SPF calculates the cost of a rout as the sum of the OSPF interface costs for all outgoing interfaces in the route. The interface cost can be set directly (ip ospf cost), or IOS uses a default based on the reference bandwidth and the interface bandwidth. Of the listed answers, delay is the only setting that does not influence OSPFv2 metric calculations.

Which of the following configuration settings on a router does not influence which IPv4 route a router chooses to add to its IPv4 routing table when using OSPFv2? -delay -bandwidth -ip ospf cost -auto-cost reference-bandwidth

-network 10.1.0.0. 0.0.255.255 area 0 The command matches all IP addresses that begin with 10.1, enabling OSPF in area 0 on all interfaces.

Which of the following network commands, following the command router ospf 1, tells this router to start using OSPF on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1? -network 10.1.0.0. 0.0.255.255 area 0 -network 10.0.0.0 0.255.255.0 area 0 -network 10.1.1.0 255.0.0.0 area 0 -network 10.0.0.0 255.0.0.0 area 0

-OSPF Process ID mismatch

Which option do no prevent a directly connected OSPF speaker from becoming a neighbor? -Area mismatch -Subnet Mask mismatch -Hello Timer mismatch -OSPF Process ID mismatch

-Link-state database To calculate the best route to input in the routing table, an OSPF router gets its information from the link-state database and uses the SPF algorithm to determine which route is the best one. Once the best route is calculated, it is then added to the routing table of the router.

Which source of information does OSPF use when calculating the best routes to input in the routing table of a router? -Hop counts -Bandwidth -Link-state database -Path

-If the DR fails, the BDR becomes the DR, and an election will occur for a new BDR. If the DR comes back online, it will not resume as DR. There will not be another DR election because the BDR has become the DR upon failure of the original DR. The new election occurs for the BDR, not the DR.

Which statement is true about the DR and BDR in OSPF? -If the DR fails, the BDR becomes the DR, and when the DR is online again, it will resume as the DR. -If the DR fails, the BDR becomes the DR, and no new election will occur for the BDR. -If the DR fails, an election will occur for a new DR. -If the DR fails, the BDR becomes the DR, and an election will occur for a new BDR.

-Connected routes -Floating static -Static routes

Which type of routes will a router add to its IP routing table if the router does not use a routing protocol? (CHOOSE 3) -Dynamic route -Connected routes -Floating static -Static routes

-Type 3 An ABR (area border router) connects to multiple OSPF areas. Each ABR creates summary information about all of the subnets in one area and advertises that information as a Type 3 LSA for each subnet into another area. Routers create a Type 1 LSA for themselves, with each router flooding their own Type 1 LSA to the other routers in the same area Similarly, one router (the DR on a subnet) creates a Type 2 LSA for any subnets on which a DR and BDR have been elected, flooding those LSAs throughout the area.

Which types of LSAs will the ABR create? -Type 0 -Type 1 -Type 2 -Type 3