300-410 Mock Exam 76 — 25 Questions

Question 1

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 2

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 3

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 4

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 5

Router R1 and R2 are OSPF neighbors over a FastEthernet link with BFD enabled. R1 has 'ip ospf network point-to-point' configured. R2 does not. After a reload, BFD sessions fail to establish. R1#show bfd neighbors shows no sessions. R2#show bfd neighbors shows no sessions. What is the root cause?

Accepted Answer

OSPF network type mismatch between R1 and R2 prevents BFD session establishment.. BFD requires matching OSPF network types on the same link for proper session establishment. When R1 is configured as point-to-point and R2 remains as broadcast, OSPF forms a neighbor relationship but BFD sessions fail because BFD expects consistent interface parameters.

Answer

BFD is not supported on FastEthernet interfaces.

Answer

BFD timers are not configured globally.

Answer

OSPF hello/dead intervals must match for BFD to work.

Question 6

A network engineer runs the following command on Router R1:

R1# show ip policy
Interface     Route-map
GigabitEthernet0/1      PBR-MAP

R1# show route-map PBR-MAP
route-map PBR-MAP, permit, sequence 10
  Match clauses:
    ip address (access-lists): 101
  Set clauses:
    ip next-hop verify-availability 10.1.1.2 10 track 1
  Policy routing matches: 150 packets, 12000 bytes

R1# show track 1
Track 1
  IP SLA 1 reachability
  Reachability is Down
    1 change, last change 00:05:20
  Latest operation return code: timeout
  Tracked by:
    ROUTE-MAP 0

Based on this output, what is the most likely outcome?

Accepted Answer

Packets matching ACL 101 are routed normally via the routing table.. The route map uses 'ip next-hop verify-availability' with tracking. Track 1 is down because IP SLA 1 reports unreachability. Therefore, the set clause will not be applied, and packets matching ACL 101 will not be forwarded to 10.1.1.2; they will be routed normally via the routing table.

Answer

Packets matching ACL 101 are forwarded to 10.1.1.2 regardless.

Answer

Packets matching ACL 101 are dropped.

Answer

The route map is removed from the interface due to the track failure.

Question 7

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 8

R1 and R2 are BGP peers with BFD enabled. R1#show bgp neighbors 10.1.1.2 shows BGP state 'Active' and BFD session 'Down'. R2#show bfd neighbors shows the session as 'Up' with R1. R1 has 'neighbor 10.1.1.2 fall-over bfd' configured. R2 has 'neighbor 10.1.1.1 fall-over bfd' configured. The link between them is stable. What is the root cause?

Accepted Answer

R1 is missing 'bfd interval' configuration on the interface facing R2.. BFD for BGP fall-over requires that the BFD session be established before BGP can form. If the BFD session is up on R2 but down on R1, it indicates a unidirectional issue. This can happen if R1 has an ACL blocking BFD control packets from R2, or if R1's BFD configuration is missing. Here, R1 likely lacks 'bfd interval' configuration on the interface, causing BFD to not initiate.

Answer

BGP requires 'neighbor 10.1.1.2 ebgp-multihop' for BFD to work.

Answer

R2 has a higher BFD multiplier causing session failure.

Answer

The BGP update-source is not set to the interface IP.

Question 9

A network engineer is troubleshooting a BGP session that is flapping. The routers are connected via a direct Ethernet cable. BFD is configured for the BGP session. The engineer checks the BFD session and sees it is 'Up'. However, the BGP session goes down every 30 seconds. The BGP configuration includes 'neighbor 10.0.0.2 fall-over bfd'. What is the most likely cause?

Accepted Answer

The BGP hold timer is set to 30 seconds on one router and 90 seconds on the other.. The BGP fall-over bfd command causes BGP to monitor the BFD session. If the BFD session is up but BGP is flapping, the issue is likely a BGP configuration problem, such as a mismatch in hold timer or update-source.

Answer

The BFD session is using echo mode, which is not supported for BGP fall-over.

Answer

The interface is configured with 'bfd interval 50 min_rx 50 multiplier 3' but the neighbor is configured with 'bfd interval 100 min_rx 100 multiplier 3'.

Answer

The BGP session is using EBGP multihop, and the TTL is set to 2.

Question 10

A network engineer is troubleshooting a BGP session that is not establishing. The routers are connected via a Layer 3 switch. BFD is configured for BGP. The engineer checks the BFD session and sees it is 'Down'. The BGP configuration appears correct. The interface between the routers is up/up. What is the most likely cause?

Accepted Answer

The BGP neighbor is not directly connected; BFD requires a directly connected interface or a static route pointing to the neighbor's IP.. BFD sessions require that the destination IP address be reachable via a directly connected interface or a static route. If the BGP neighbor is not directly connected (e.g., via a loopback), BFD may fail if the next hop is not directly connected or if there is a routing issue.

Answer

The Layer 3 switch is not configured for BFD, causing it to drop BFD packets.

Answer

The BGP session is using EBGP multihop, and the TTL is set to 1.

Answer

The interface is configured with 'bfd interval 50 min_rx 50 multiplier 3' but the neighbor is not configured for BFD.

Question 11

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 12

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 13

Which TWO configuration steps are required to enable BFD for OSPF on a Cisco IOS-XE router? (Choose TWO.)

Accepted Answer

Configure 'bfd' under the interface. To enable BFD for OSPF, you must first enable BFD on the interface using the 'bfd' interface command, and then enable BFD support for OSPF under the OSPF routing process with 'bfd all-interfaces' or per-neighbor. The other options are either incorrect or not required.

Answer

Configure 'ip ospf bfd' under the interface

Answer

Configure 'bfd interval 50 min_rx 50 multiplier 3' globally

Answer

Configure 'router bfd' globally

Question 14

A network engineer is troubleshooting an OSPF adjacency that is not forming. Both routers are running OSPF with BFD enabled. The engineer checks the BFD session and sees it is 'Up'. However, the OSPF neighbor state is stuck in 'INIT'. What is the most likely cause?

Accepted Answer

The OSPF area ID is mismatched between the two routers.. OSPF stuck in INIT usually indicates that the router is not receiving OSPF hello packets from the neighbor. BFD being up suggests Layer 2 connectivity is fine, so the issue is likely OSPF configuration, such as a mismatch in area ID or authentication.

Answer

The OSPF hello interval is mismatched between the two routers.

Answer

The OSPF network type is mismatched (e.g., broadcast vs point-to-point).

Answer

The interface is configured with 'ip ospf bfd' but the OSPF process is not configured with 'bfd all-interfaces'.

Question 15

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      Down          0(0)          Gi0/0

Session state is DOWN
OurAddr: 10.1.1.1
Handle: 1
Local Diag: 1, Demand mode: 0, Poll bit: 0
MinTxInt: 1000000, MinRxInt: 1000000, Multiplier: 3
Received MinRxInt: 1000000, Received Multiplier: 3
Holddown (hits): 0(0)
Rx Count: 0, Tx Count: 50

Based on this output, what is the most likely cause of the BFD session being down?

Accepted Answer

The BFD session is down because the neighbor is not responding to BFD packets, likely due to a network connectivity issue or neighbor misconfiguration.. The Local Diag field shows 1, which indicates 'Control Detection Time Expired'. This means the local router did not receive BFD control packets from the neighbor within the expected time. The Rx Count is 0, confirming no packets were received. Tx Count is 50, so the local router is sending packets but not receiving any.

Answer

The neighbor router is not configured for BFD.

Answer

The BFD session is down because the local router is not sending BFD packets.

Answer

The BFD session is down because the multiplier is set too low.

Question 16

Which TWO statements about route targets (RT) in MPLS L3VPN are true? (Choose TWO.)

Accepted Answer

The import RT is used to filter incoming VPNv4 routes into a VRF on the receiving PE.. Route targets control the import and export of VPNv4 routes between VRFs. The export RT is attached to routes when they are advertised from a VRF to MP-BGP. The import RT determines which routes are imported into a VRF. RTs are not used for label distribution (LDP handles that) and do not affect the IGP. They are not directly involved in the VRF route distinguisher (RD) process, though RD and RT are often configured together.

Answer

The export RT is added to VPNv4 routes when they are advertised from a PE to a P router.

Answer

Route targets are used by LDP to distribute VPN labels between PEs.

Answer

The route target must match the route distinguisher for the VRF to function.

Question 17

Which SNMP version introduced the use of a User-based Security Model (USM) and View-based Access Control Model (VACM)?

Accepted Answer

SNMPv3. SNMPv3 introduced the User-based Security Model (USM) for authentication and encryption, and the View-based Access Control Model (VACM) for granular access control. These models provide message integrity, authentication, and encryption, addressing the security deficiencies of earlier SNMP versions.

Answer

SNMPv1

Answer

SNMPv2c

Answer

SNMPv2u

Question 18

Drag and drop the steps to verify and validate BGP operational state into the correct order, from first to last.

Accepted Answer

Check BGP summary for session state. Start by checking the BGP summary for session state; then examine the BGP table for received prefixes; next verify prefix advertisement with show ip bgp neighbors; then check route propagation with show ip route bgp; finally validate path selection with show ip bgp bestpath.

Question 19

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

Question 20

A network engineer is troubleshooting an IPv6 neighbor discovery issue on a switch running IOS-XE. Hosts on VLAN 100 are intermittently losing connectivity to the default gateway. The switch is configured with IPv6 First Hop Security features including RA Guard and DHCPv6 Guard. The engineer notices that the switch is dropping valid Router Advertisements from the legitimate router. What is the most likely cause of this issue?

Accepted Answer

The RA Guard policy is configured with 'device-role router' on the port connected to the legitimate router, but the router's MAC address is not in the allowed list.. The RA Guard policy with 'device-role router' on the port connected to the legitimate router expects the router's MAC address to be in an allowed list. If the MAC address is not explicitly permitted, the switch drops all Router Advertisements from that port, including valid ones. This causes hosts on VLAN 100 to lose connectivity to the default gateway because they never receive the necessary RA to learn the gateway's IPv6 address and on-link prefix.

Answer

DHCPv6 Guard is blocking DHCPv6 Advertise messages from the router, preventing hosts from obtaining IPv6 addresses.

Answer

IPv6 Source Guard is dropping packets from the router because the router's IPv6 address is not in the binding table.

Answer

The switch has IPv6 unicast-routing enabled, causing it to send its own RAs and override the legitimate router.