300-410 Bidirectional Forwarding Detection (BFD) Practice Test 2 — 15 Questions

Question 1

A network engineer runs the following command on Router R1:

R1# show bfd neighbors detail

IPv4 Sessions
NeighborAddr      LD/RD         Int        State         Holdown(mult)  Intf
10.1.1.2          1/3           Gi0/0      Up            3000(3)        Gi0/0

Session state is UP and not using echo function.
OurAddr: 10.1.1.1
Handle: 1
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
Received MinRxInt: 1000000, Received Multiplier: 3
Holddown (hits): 3000(0)
Rx Count: 100, Tx Count: 100

Based on this output, what is the BFD session's detection time?

Accepted Answer

The detection time is 3000 ms.. The detection time is the holddown timer, which is the negotiated transmit interval multiplied by the multiplier. The negotiated transmit interval is 1000 ms (maximum of local MinTxInt and received MinRxInt), and the multiplier is 3, so the detection time is 3000 ms.

Answer

The detection time is 1000 ms.

Answer

The detection time is 1500 ms.

Answer

The detection time is 9000 ms.

Question 2

A network engineer runs the following command on Router R1:

R1# show bfd neighbors detail

IPv4 Sessions
NeighborAddr      LD/RD         Int        State         Holdown(mult)  Intf
10.1.1.2          1/3           Gi0/0      Up            3000(3)        Gi0/0

Session state is UP and not using echo function.
OurAddr: 10.1.1.1
Handle: 1
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
Received MinRxInt: 1000000, Received Multiplier: 3
Holddown (hits): 3000(0)
Rx Count: 100, Tx Count: 100

Based on this output, what is the BFD session's local discriminator?

Accepted Answer

The local discriminator is 1.. The local discriminator is the LD value shown in the output. In this case, it is 1.

Answer

The local discriminator is 3.

Answer

The local discriminator is 10.1.1.1.

Answer

The local discriminator is 10.1.1.2.

Question 3

A network engineer runs the following command on Router R1:

R1# show bfd neighbors detail

IPv4 Sessions
NeighborAddr      LD/RD         Int        State         Holdown(mult)  Intf
10.1.1.2          1/3           Gi0/0      Up            3000(3)        Gi0/0

Session state is UP and not using echo function.
OurAddr: 10.1.1.1
Handle: 1
Local Diag: 0, Demand mode: 0, Poll bit: 0
MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
Received MinRxInt: 1000000, Received Multiplier: 3
Holddown (hits): 3000(0)
Rx Count: 100, Tx Count: 100

Based on this output, what is the BFD session's remote discriminator?

Accepted Answer

The remote discriminator is 3.. The remote discriminator is the RD value shown in the output. In this case, it is 3.

Answer

The remote discriminator is 1.

Answer

The remote discriminator is 10.1.1.2.

Answer

The remote discriminator is 10.1.1.1.

Question 4

Consider the following partial configuration on a router:

interface GigabitEthernet0/1
 ip address 10.1.1.1 255.255.255.252
 bfd interval 100 min_rx 100 multiplier 3
!
router ospf 1
 network 10.1.1.0 0.0.0.3 area 0
!

What is the effect of this configuration?

Accepted Answer

BFD is configured on the interface but will not be used by OSPF unless the 'bfd all-interfaces' command is added under router ospf.. The BFD configuration is applied under the interface, but OSPF must be explicitly configured to use BFD via the 'bfd all-interfaces' command under the OSPF routing process. Without this, BFD will not be used for OSPF neighbor failure detection.

Answer

BFD is enabled for OSPF on this interface and will detect failures faster than OSPF's hello/dead timers.

Answer

BFD will only be used if the neighbor also has BFD configured with the same timer values.

Answer

The BFD configuration is invalid because the interval and min_rx values must be identical on both sides.

Question 5

Examine the following configuration:

interface GigabitEthernet0/0
 ip address 192.168.1.1 255.255.255.0
 bfd interval 50 min_rx 50 multiplier 5
!
router eigrp TEST
 network 192.168.1.0
 bfd interface GigabitEthernet0/0
!

Which statement is true about BFD operation on this interface?

Accepted Answer

BFD will detect a failure in 250 ms (5 x 50 ms).. The 'bfd interface' command under EIGRP enables BFD for that specific interface. The BFD session will negotiate timers; the multiplier of 5 means the session will declare a neighbor down after 5 * max(min_rx, negotiated interval) = 5 * 50 = 250 ms of missed packets.

Answer

BFD will detect a failure in 50 ms because the interval is set to 50 ms.

Answer

BFD is enabled but only for EIGRP; it will not affect any other routing protocol.

Answer

The configuration is missing 'bfd all-interfaces' under EIGRP, so BFD will not work.

Question 6

A network engineer has configured BFD for OSPF as shown:

interface GigabitEthernet0/0
 bfd interval 300 min_rx 300 multiplier 3
!
router ospf 1
 bfd all-interfaces
!

However, BFD sessions are not coming up. What is the most likely missing configuration?

Accepted Answer

The interface has no IP address configured.. BFD requires that the interface has an IP address and is up/up. The configuration shown lacks an IP address on the interface, which is necessary for BFD to establish a session.

Answer

The 'bfd all-interfaces' command should be replaced with 'bfd interface GigabitEthernet0/0'.

Answer

The BFD timers must be set to 100 ms or less for OSPF.

Answer

The router must be configured with 'bfd map' commands for each neighbor.

Question 7

Consider the following BGP configuration with BFD:

router bgp 65000
 neighbor 10.1.1.2 remote-as 65001
 neighbor 10.1.1.2 fall-over bfd
!
interface GigabitEthernet0/0
 ip address 10.1.1.1 255.255.255.252
 bfd interval 200 min_rx 200 multiplier 4
!

What is the effect of the 'neighbor fall-over bfd' command?

Accepted Answer

BGP will use BFD for fast failure detection; if BFD goes down, BGP will reset the session immediately.. The 'neighbor fall-over bfd' command enables BGP to use BFD for fast failure detection. When BFD detects a failure, BGP will immediately tear down the peering session without waiting for the hold timer.

Answer

BGP will use BFD to detect link failures, but the BGP hold timer still applies.

Answer

BGP will ignore the BFD session and continue using its own keepalive/hold mechanism.

Answer

The 'fall-over bfd' command is only needed if BFD timers are less than 100 ms.

Question 8

Examine the partial BFD configuration on a router:

interface GigabitEthernet0/0
 bfd interval 100 min_rx 100 multiplier 3
!
interface GigabitEthernet0/1
 bfd interval 200 min_rx 200 multiplier 3
!
router ospf 1
 bfd all-interfaces
!

The router has OSPF neighbors on both interfaces. Which statement is true?

Accepted Answer

The BFD session on GigabitEthernet0/0 will detect failures in 300 ms, and on GigabitEthernet0/1 in 600 ms.. BFD timers are configured per interface. Each BFD session independently uses the timers configured on its respective interface. The multiplier is applied per session.

Answer

Both BFD sessions will use the same timer values because OSPF is configured with 'bfd all-interfaces'.

Answer

The BFD session on GigabitEthernet0/1 will not form because the interval is too high.

Answer

The router will use the minimum interval across all interfaces for consistency.

Question 9

A router has the following BFD configuration for a static route:

ip route 10.0.0.0 255.255.255.0 192.168.1.2
bfd map 192.168.1.2 10.0.0.0 255.255.255.0
interface GigabitEthernet0/0
 ip address 192.168.1.1 255.255.255.0
 bfd interval 100 min_rx 100 multiplier 3
!

What is the purpose of the 'bfd map' command in this context?

Accepted Answer

It creates a BFD session to the next-hop 192.168.1.2 and associates it with the static route to 10.0.0.0/24.. For static routes, BFD must be explicitly mapped to the next-hop and destination prefix. The 'bfd map' command associates a BFD session with a static route so that if BFD detects a failure, the static route is removed from the routing table.

Answer

It maps the BFD session to the interface, enabling BFD for all static routes using that interface.

Answer

It maps the BFD session to the OSPF process, which is incorrect for static routes.

Answer

It is used to configure BFD for multiple static routes simultaneously.

Question 10

What is the default BFD interval and multiplier on Cisco IOS-XE devices when BFD is enabled under an interface without explicit timer configuration?

Accepted Answer

interval 150 ms, min_rx 150 ms, multiplier 3. If no BFD timers are configured under the interface, the default values are: interval = 150 ms, min_rx = 150 ms, multiplier = 3. These are the defaults used when 'bfd interval' is not specified.

Answer

interval 100 ms, min_rx 100 ms, multiplier 3

Answer

interval 200 ms, min_rx 200 ms, multiplier 5

Answer

interval 50 ms, min_rx 50 ms, multiplier 3

Question 11

Which of the following statements about BFD echo mode is true?

Accepted Answer

Echo mode allows the local router to detect failures without requiring the remote router to send BFD control packets.. BFD echo mode is an optional mode where the local router sends echo packets to the remote router, which loops them back. This reduces the processing load on the remote router because it does not need to generate BFD control packets. Echo mode is enabled by default on Cisco IOS-XE.

Answer

Echo mode increases the load on the remote router because it must process echo packets.

Answer

Echo mode is disabled by default and must be explicitly enabled.

Answer

Echo mode uses the same timer values as the BFD control packets.

Question 12

According to RFC 5880, what is the maximum number of BFD sessions that can be supported by a single interface on a Cisco router?

Accepted Answer

Unlimited, but limited by platform resources. RFC 5880 does not specify a maximum number of BFD sessions per interface; it is platform-dependent. Cisco routers can support multiple BFD sessions per interface, limited only by hardware resources.

Answer

1 session per interface

Answer

256 sessions per interface

Answer

16 sessions per interface

Question 13

Which TWO commands can be used to verify the operational state of BFD sessions on a Cisco IOS-XE router? (Choose TWO.)

Accepted Answer

show bfd neighbors. The 'show bfd neighbors' command displays BFD session details such as neighbor address, interface, state, and timers. The 'show bfd session' command provides similar information, including the local discriminator and session state. The other commands are either unrelated or do not show BFD session state.

Answer

show ip route

Answer

show bfd statistics

Answer

show running-config | include bfd

Question 14

Which TWO statements about BFD echo mode are true? (Choose TWO.)

Accepted Answer

Echo packets are generated by the sending router and forwarded back by the remote router.. In BFD echo mode, the sending router generates echo packets that are looped back by the remote router, allowing detection of failures without involving the remote router's control plane. This reduces CPU load on the remote router. The other statements are false because echo mode does not require a separate session for each direction, and it does not increase the number of BFD control packets.

Answer

Echo mode requires a separate BFD session for each direction.

Answer

Echo mode increases the number of BFD control packets sent between routers.

Answer

Echo mode is enabled by default on all interfaces.

Question 15

Which THREE symptoms indicate a BFD session failure? (Choose THREE.)

Accepted Answer

The BFD neighbor state shows 'Down'. A BFD session failure typically results in the neighbor state being 'Down', the routing protocol (like OSPF or EIGRP) neighbor going down due to BFD's fast detection, and BFD timers expiring. The other options are not direct symptoms of a BFD session failure.

Answer

The interface MTU is set to 1500

Answer

The BFD discriminator value is zero