What F5CAB2 Questions and Answers feature?

For BIG-IP to send or receive traffic on a VLAN, that VLAN must be bound to a physical interface or a trunk . Creating a VLAN object and a Self IP alone is not sufficient to establish data-plane connectivity.

From the exhibit:

The VLAN ( vlan_1033 ) exists and has a tag defined.

A Self IP is configured and associated with the VLAN.

However, traffic cannot reach servers on that VLAN.

This indicates a Layer 2 connectivity issue , not a Layer 3 or HA issue.

Why assigning a physical interface fixes the problem:

BIG-IP VLANs do not carry traffic unless they are explicitly attached to:

A physical interface (e.g., 1.1), or

A trunk

Without an interface assignment, the VLAN is effectively isolated and cannot transmit or receive frames, making servers unreachable regardless of correct IP addressing.

Why the other options are incorrect:

A. Set Port Lockdown to Allow All Port Lockdown controls which services can be accessed on the Self IP (management-plane access), not whether BIG-IP can reach servers on that VLAN.

B. Change Auto Last Hop to enabled Auto Last Hop affects return traffic routing for asymmetric paths. It does not fix missing Layer 2 connectivity.

D. Create a Floating Self IP address Floating Self IPs are used for HA failover. They do not resolve reachability issues on a single device when the VLAN itself is not connected to an interface.

Conclusion:

The servers are unreachable because the VLAN has no physical interface assigned . To restore connectivity, the BIG-IP Administrator must assign a physical interface (or trunk) to the VLAN , enabling Layer 2 traffic flow.

To meet the requirement of fault tolerance when one interface goes down , BIG-IP must use link aggregation so that loss of a single physical link does not isolate the VLAN(s).

How the objects relate (data plane view)

Interfaces = physical links.

Trunk (LACP) = bundles multiple interfaces into one logical link that provides redundancy (and possibly bandwidth aggregation).

VLANs are assigned to interfaces or trunks. If you need multiple VLANs on the same trunk , they must use 802.1Q tagging (because you can only have one untagged VLAN per interface/trunk).

Self IPs are then placed on the VLANs to provide BIG-IP presence and routing/ARP functions, but self IPs are not what provides link resiliency— the trunk does .

Why Option D is correct

You have two physical interfaces and you want resiliency if one fails → put both interfaces into one trunk with LACP enabled .

You need both external and internal VLANs on those same two links → both VLANs should be configured as tagged on that trunk, so they can coexist on the same aggregated link.

If either physical interface fails, the trunk remains up via the remaining interface, keeping both VLANs operational .

Why the other options are incorrect

A : Two VLANs cannot both be untagged on the same trunk/interface. Only one untagged VLAN is possible; additional VLANs must be tagged.

B : Two trunks “each with one VLAN” would typically mean splitting VLANs across separate trunks. With only two interfaces total, that becomes one interface per trunk—if one interface goes down, the VLAN on that interface is down (no redundancy for that VLAN).

C : Same redundancy problem as B, and disabling LACP removes the negotiated aggregation behavior expected when the switch engineer specifically requested LACP.

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This question tests understanding of Priority Group Activation (PGA) and how BIG-IP determines which pool members are eligible to receive traffic.

Key BIG-IP Priority Group Concepts:

Higher priority group numbers = higher priority

BIG-IP will only send traffic to the highest priority group that meets the Priority Group Activation condition

Lower priority groups are activated only when the condition is met

Only available (green) members count toward the activation threshold

Configuration from the Exhibit:

Priority Group Activation: Less than 2 available members

Pool Members and Status:

Pool Member

Priority Group

Status

serv1

2

Active (available)

serv2

2

Inactive (down)

serv3

1

Active (available)

serv4

1

Active (available)

Step-by-Step Traffic Decision:

BIG-IP first evaluates the highest priority group (Priority Group 2)

Priority Group 2 has:

serv1 → available

serv2 → unavailable

Total available members = 1

Activation rule is Less than 2 available members

Condition is true (1 < 2)

BIG-IP activates the next lower priority group (Priority Group 1)

Traffic is now sent to:

serv1 (Priority Group 2)

serv3 and serv4 (Priority Group 1)

Final Result:

Traffic is distributed to serv1, serv3, and serv4

Why the Other Options Are Incorrect:

A – Ignores activation of the lower priority group

B – serv4 is also active and eligible

C – serv2 is down and cannot receive traffic

Key Data Plane Concept Reinforced:

Priority Group Activation controls when lower-priority pool members are allowed to receive traffic , based strictly on the number of available members in the higher-priority group. In this case, the failure of one high-priority member caused BIG-IP to expand traffic distribution to lower-priority members to maintain availability.

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