F5 BIG-IP Administration Data Plane Concepts (F5CAB2) exam F5CAB2 Exam Dumps: Updated Questions & Answers (February 2026)

In a High Availability (HA) environment, a failover event occurs when the active BIG-IP system stops processing traffic and the standby unit takes over. This transition can cause a brief disruption in network traffic because the surrounding switches need to update their ARP tables to associate the Virtual IP (VIP) and floating Self-IPs with the MAC address of the new active unit.

MAC Masquerade Functionality:To minimize this impact, an administrator can configureMAC masquerading. This feature allows the administrator to assign a unique, "shared" MAC address to a traffic group.

Seamless Transition:When a failover occurs, the new active unit begins using this shared MAC address immediately. Since the MAC address for the traffic group remains the same regardless of which physical device is active, the upstream switches do not need to update their ARP tables or learn a new MAC-to-port mapping.

Packet Loss Reduction:By maintaining a constant MAC address, MAC masquerading significantly reduces the time it takes for traffic to resume, effectively eliminating the "gratuitous ARP" dependency and minimizing packet loss during the handover.

Why other options are incorrect:

External monitors:These are used for advanced health checking of pool members and do not directly impact the speed or smoothness of a device-level failover.

OneConnect profile:This is a performance optimization tool that aggregates multiple client-side requests into a single server-side TCP connection; it is not a failover mechanism.

Clone pool:This is used to replicate traffic for IDS or monitoring purposes and has no role in high availability or failover optimization.

The BIG-IP system supports various remote authentication methods like LDAP, Active Directory, and RADIUS.

Fallback to Local:This is a specific security and availability feature within theSystem > Users > Authenticationconfiguration.

Redundancy:When "Fallback to Local" is enabled, the BIG-IP will first attempt to authenticate a user against the configured remote server. If that remote server is unreachable or fails to respond, the system will then check its internalLocal User databasefor credentials.

Administrative Access:This is standard practice for the "admin" or emergency accounts to ensure the system remains accessible even if the corporate directory service (e.g., AD) is offline.

In anActive/StandbyBIG-IP design, application availability during failover depends on both units havingequivalent data-plane connectivityfor the networks that carry application traffic. Specifically:

VLANs are bound to specific interfaces (and optionally VLAN tags).

Floating self IPs / traffic groupsmove to the new Active device during failover.

For traffic to continue flowing after failover, the new Active device must have thesame VLANs available on the correct interfacesthat connect to the upstream/downstream networks.

What the symptom tells you:

Traffic works when Device A is Active

Traffic fails when Device B becomes Active

Failback immediately restores traffic

This pattern strongly indicates theStandby unit does not have the VLAN connected the same way(wrong physical interface assignment), so when it becomes Active, it owns the floating addresses but cannot actually pass traffic on the correct network segment.

WhyInterface mismatchis the best match:

If theActiveunit is already working, its interface mapping is correct.

The fix is to make theStandbyunit’s VLAN/interface assignment match the Active unit.

That corresponds tochanging the Standby device interface to 1.1.

Why theTagoptions are less likely here (given the choices and the exhibit intent):

Tag issues can also break failover traffic, but the question/options are clearly driving toward the classic HA requirement:consistent VLAN-to-interface mapping on both devicesso the data plane remains functional after the traffic group moves.

Conclusion:To avoid an outage on the next failover, the BIG-IP Administrator must ensure the Standby device uses thesame interface (1.1)for the relevant VLAN(s) that carry the application traffic, so when it becomes Active it can forward/receive traffic normally.

In the BIG-IP system, VLANs are the logical entities that group physical interfaces or trunks together. To modify how a VLAN interacts with an interface, the administrator must navigate to the specific VLAN configuration object.

VLAN List:This section displays all existing VLANs configured on the system.

Interface Association:Within the properties of a specific VLAN (in this case, "external"), there is anInterfacessection. This is where physical ports or trunks are assigned to the VLAN.

Tagging Status:For each associated interface, the administrator can choose betweenTagged(802.1Q) orUntagged.

Untagged:The interface will treat incoming traffic without a VLAN header as part of this VLAN, and outgoing traffic will not have a VLAN tag added. An interface can only be "Untagged" for one VLAN.

Tagged:Allows an interface to carry traffic for multiple VLANs simultaneously by using 802.1Q headers.

To meet the requirement offault tolerance when one interface goes down, BIG-IP must uselink aggregationso 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 providesredundancy(and possibly bandwidth aggregation).

VLANsare assigned to interfaces or trunks. If you needmultiple VLANs on the same trunk, they must use802.1Q tagging(because you can only have one untagged VLAN per interface/trunk).

Self IPsare 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 havetwo physical interfacesand you want resiliency if one fails → put both interfaces intoone trunk with LACP enabled.

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

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

Why the other options are incorrect

A: Two VLANs cannot both beuntaggedon 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.

===========

In the BIG-IP system object hierarchy, health monitors can be applied at three levels:Node,Pool, andPool Member.

Pool Level (Properties):Applying a monitor at thePool > Propertieslevel is the most common and efficient administrative practice. When applied here, the monitor is inherited by all members of that pool. If the monitor fails for a specific member, that member is marked "down" specifically for that pool.

Node Level:If a monitor is applied at the Node level (Local Traffic > Nodes), it checks the health of the physical IP address itself. If it fails, that node (and all pool members associated with it) is marked down globally across the entire system.

Member Level:Applying a monitor at thePool > Memberslevel allows for specific "per-member" monitoring, which is usually only done if different members in the same pool require different health checks.

The Specific Case:For a standard database pool like DB_Pool, the administrator should navigate toLocal Traffic > Pools > DB_Pool > Propertiesand select the appropriate monitor (e.g., a custom TCP or Oracle monitor) from the "Health Monitors" configuration section.

For BIG-IP to send or receive traffic on a VLAN, that VLANmust be bound to a physical interface or a trunk. Creating a VLAN object and a Self IP alone isnot sufficientto 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 aLayer 2 connectivity issue, not a Layer 3 or HA issue.

Whyassigning a physical interfacefixes the problem:

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

Aphysical interface(e.g., 1.1), or

Atrunk

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 AllPort Lockdown controls which services can be accessedon the Self IP(management-plane access), not whether BIG-IP can reach servers on that VLAN.

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

D. Create a Floating Self IP addressFloating 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 hasno physical interface assigned. To restore connectivity, the BIG-IP Administrator mustassign a physical interface (or trunk) to the VLAN, enabling Layer 2 traffic flow.

This question tests understanding ofPriority 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 willonly send traffic to the highest priority groupthat meets thePriority Group Activationcondition

Lower priority groups areactivated only when the condition is met

Onlyavailable (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 thehighest priority group (Priority Group 2)

Priority Group 2 has:

serv1 → available

serv2 → unavailable

Total available members = 1

Activation rule isLess than 2 available members

Condition istrue(1 < 2)

BIG-IPactivates 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 toserv1, 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 ofavailable membersin the higher-priority group. In this case, the failure of one high-priority member caused BIG-IP toexpand traffic distributionto lower-priority members to maintain availability.

===========

This scenario combinessession continuity,multiple protocols (HTTP and FTP), andHA failover behavior, which directly implicatespersistence handling across devices and services.

Key Requirements Breakdown

Samepool member for entire session

Session must survivefailover

Session must spanmultiple services (HTTP and FTP)

Why Persistence Mirroring + Match Across Services Is Required

Persistence Mirroring

Ensurespersistence records are synchronizedfrom the active BIG-IP to the standby BIG-IP.

Without mirroring:

After failover, the standby device hasno persistence table

Clients are load-balanced again

Sessions break, forcing users to restart

Persistence mirroring is essential forsession continuity during failover

Match Across Services

Allows asingle persistence recordto be shared acrossmultiple virtual servers / protocols

Required when:

HTTP and FTP must use thesame pool member

Multiple services are part of a single application session

Together, these settings ensure:

Persistence survivesdevice failover

Persistence is honoredacross HTTP and FTP

Why the Other Options Are Incorrect

A. Cookie persistence and session timeoutCookie persistence only applies to HTTP and does not address FTP or failover synchronization.

B. Stateful failover and Network Failover detectionStateful failover applies toconnection state, notpersistence records, and does not link HTTP and FTP sessions.

D. SYN-cookie insertion threshold and connection low-water markThese are DoS / SYN flood protection settings, unrelated to persistence or HA behavior.

4647

Virtual Servers have a setting calledVLAN and Tunnel Trafficwhich defines where the BIG-IP "listens" for new connections.4849

Ingress Logic:A virtual server is an entry point. It must be enab50led on the VLAN where theClientresides. If a client is on the "51Internal" VLAN, the Virtual Server must be enabled there to receive the traffic.

Egress Logic:The BIG-IP system uses theTMM Routing TableandSelf-IPsto reach pool members. It doesnotneed the Virtual Server to be "enabled" on the destination VLAN (External) to send traffic there.

Default Behavior:By default, Virtual Servers are enabled on "All VLANs." However, if restricted for security, the administrator must ensure the Virtual Server is active on the client-facing (ingress) VLAN.