Volume 1 - Chapter 23: Implementing Optional OSPF Features Flashcards
Which OSPF network type supports the use of a DR/BDR?
Broadcast
Which OSPF network type does not support the use of a DR/BDR?
Point-to-Point
An OSPF-enabled router has a connection to a LAN on its Gi0/1 interface, but no other routers share that LAN.
What role will the Gi0/1 be by default?
The designated router
Describe the process for electing a BR/BDR.
The router elected to become the DR is the router with the highest OSPF interface priority.
If all priorities tie, then the router with the highest RID wins.
What is the range of values available for an OSPF interface priority?
0 to 255.
What OSPF interface priority will prevent a router from ever becoming a DR?
0
What is the default OSPF interface priority?
1
A technician configures R2 with an interface priority of 95 to attempt to make it the DR on a LAN shared with 3 other routers. All other routers use default priorities, what happens when the technician updates the priority?
Nothing, changing the interface priority does not cause a new DR/BDR election. Only a failure on the network will cause the routers to elect R2 as the DR.
What is the default setting enabled on Serial interfaces?
ip ospf network point-to-point
What type of OSPF network type is used on E-Line (Private Wire Services)?
Point to Point
A technician connects R1 & R2 together over a direct point-to-point link. What neighbor state would you expect to see on either router when running the following command?:
show ip ospf neighbor
FULL/-
Describe how the OSPF process changes on a port when a technician configures it to be a passive interface?
1) OSPF will continue to advertise the subnet.
2) OSPF no longer sends hello messages on the interface.
3) OSPF no longer processes any received hellos.
What commands can be used to configure passive interfaces?
passive-interface type number
Or
passive-interface default
A technician has configured all interfaces to be passive by default. What command is used stop interface Gi0/0/1 from being passive?
no passive-interface GigabitEthernet0/0/1
What command(s) are used to advertise a default route to 0.0.0.0 /0 to OSPF enabled routers?
1) Set the default route on the edge router:
ip route 0.0.0.0 0.0.0.0 nexthop
2) Configure the router to advertise the default route:
default-information originate
What command is used in OSPF to advertise a default route, even when no default route currently exists?
default-information originate always
What interface subcommand can be used to statically set a port’s cost metric?
ip ospf cost x
What is the command to set an interfaces bandwidth metric?
bandwidth speed
How does OSPF calculate the cost of an interface that does not have a cost statically configured?
Using the following formula:
Cost = ref_bandwidth (kbps) / interface bandwidth (kbps)
What is the default reference bandwidth used on Cisco routers?
100 Mbps
What is the minimum OSPF interface cost?
1
Describe the problem with utilizing the default reference bandwidth?
All links that are 100 Mbps or faster are treated the same in terms of cost:
Cost = ref_bandwidth (kbps) / interface bandwidth (kbps)
100,000 / 100,000 = 1
100,000 / 1,000,000 = 1 (minimum is 1)
100,000 / 10,000,000 = 1 (minimum is 1)
What command is used to change the default interface reference bandwidth?
auto-cost reference-bandwidth speed
Speed is in Mbps
What are the range of values for a statically assigned OSPF interface cost?
Between 1 and 65,535.
What is the default hello interval on OSPF enabled interfaces for IOS?
10 seconds.
What is the default dead interval on OSPF enabled interfaces for IOS?
40 seconds.
What interface subcommands are configured to statically set the hello and dead intervals?
ip ospf hello-interval x
ip ospf dead-interval x
