In BIG-IP architecture,link aggregation and redundancyat Layer 2 are implemented usingTrunks, not virtual servers or pools.

According to BIG-IP Administration Data Plane Concepts:

Interfacesare the physical network ports on the BIG-IP device

ATrunkis a logical grouping of multiple interfaces

Trunks can be configured to useLACP (Link Aggregation Control Protocol)to:

Provide link redundancy

Increase aggregate bandwidth

Allow automatic detection of link failures

VLANs are thenassigned to the trunk, not directly to individual interfaces, once aggregation is in place

Correct Design for the Scenario:

To connect BIG-IP totwo upstream switcheswith LACP:

One physical interface from BIG-IP connects toSwitch A

Another physical interface from BIG-IP connects toSwitch B

Both interfaces are placed intothe same trunk

LACP is enabled on the trunk and on the switches

This configuration allows:

Traffic to continue flowing if one interface or switch fails

Proper LACP negotiation between BIG-IP and the upstream switches

Clean separation of responsibilities (Layer 2 handled by trunking, Layer 4–7 by virtual servers)

Why Option D Is Correct:

ATrunk containing an interface connected to each switchis exactly how BIG-IP implements LACP-based interface binding

The trunk handles link state, load distribution, and failover at the data plane

Why the Other Options Are Incorrect:

A & B– Virtual servers operate at Layers 4–7 and have nothing to do with physical link aggregation or LACP

C– VLAN IDs and MAC addresses are not configuredinsidea trunk definition; trunks aggregate interfaces, and VLANs are appliedtotrunks

Key Data Plane Concept Reinforced:

On BIG-IP systems,LACP is always configured on a Trunk, which aggregates physical interfaces to provideLayer 2 resiliency and bandwidth aggregation. Virtual servers and pools are not involved in physical interface binding.

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The behavior of a health monitor is determined by itsSend StringandReceive String.

Default HTTP Monitor:The pre-configured default HTTP monitor on a BIG-IP system has an emptyReceive String.

Success Criteria:When the Receive String is blank, the BIG-IP system considers the health check successful if it receivesany valid HTTP responsefrom the server.

Status Code Interpretation:Because a 404 Not Found is a valid HTTP status code (it is a properly formatted response from a running web server process), the BIG-IP interprets this as the application being "alive".

Result:All three members (including the two returning 404s and the one returning 200) will be marked asUP/Available(Green).

In a BIG-IP environment, load balancing and persistence work together but serve different purposes. While a load balancing method likeLeast Connectionsattempts to distribute traffic based on current connection counts, apersistence profileoverrides this logic for returning clients.

Persistence Overrides Load Balancing:When a persistence profile (such as Source Address or Cookie persistence) is applied to a Virtual Server, the BIG-IP system tracks which client was sent to which backend member.

Sticky Sessions:If a client with a valid persistence record returns, the BIG-IP will send that client to thesame pool memberit was previously assigned to, regardless of the load balancing algorithm's current preference.

Uneven Distribution:If certain clients generate significantly more traffic or stay connected longer than others, the persistence table will "lock" those high-volume flows to specific members, resulting in an uneven distribution of connections across the pool.

Although remote authentication (LDAP, RADIUS, TACACS+) is acontrol-plane / management-planefeature, it directly affectsavailability and resiliency of administrative access, which is a critical operational HA consideration.

How BIG-IP Remote Authentication Works:

BIG-IP can authenticate administrators against:

LDAP

RADIUS

TACACS+

When remote authentication is enabled, BIG-IPby default relies on the remote serverfor user authentication

If the remote authentication server becomes unreachable, administrators may belocked outunless fallback is configured

Why “Fallback to Local” Is Required:

TheFallback to Localoption allows BIG-IP to:

Attempt authentication against theremote authentication server first

If the remote server isunreachable or unavailable, fall back to:

Local BIG-IP user accounts (admin, or other locally defined users)

This ensures:

Continuous administrative access

Safe recovery during:

Network outages

Authentication server failures

Maintenance windows

This behavior is explicitly recommended as abest practicein BIG-IP administration to avoid loss of management access.

Why the Other Options Are Incorrect:

A. Configure a second remote user directory

Provides redundancyonly if both directories are reachable

Does not help if remote authentication as a whole is unavailable

B. Configure a remote role group

Maps remote users to BIG-IP roles

Does not affect authentication availability

D. Set partition access to “All”

Controls authorization scope after login

Has no impact on authentication success

Key Availability Concept Reinforced:

To maintainadministrative access resiliency, BIG-IP administrators should always enableFallback to Localwhen using remote authentication. This prevents lockouts and ensures access even during authentication infrastructure failures.

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Managing the lifecycle of a pool member requires understanding the difference between "Disabled" and "Forced Offline" states, especially when persistence is involved.

Disabled (User-Disabled): This state allows existing connections and persistent sessions to continue until they naturally time out or are closed by the client/server. It only preventsnewsessions from being established.

Forced Offline: This state is more restrictive; it allows existing connections to complete butrejectsall new connections, including those with existing persistence records.

Immediate Removal: Neither "Disabled" nor "Forced Offline" will instantly kill currently active, established TCP connections. To meet the requirement of "immediately" removing all connections, the administrator must first set the member toForced Offline(to prevent persistence from bringing in new traffic) and then use the command line (e.g., tmsh delete sys connection ss-server-addr [IP]) to clear the current connection table entries.

In the BIG-IP object hierarchy, the destination port for backend traffic is defined at thePool Memberlevel. While a Virtual Server listens on a specific port, the Pool determines where that traffic is directed after the load balancing decision is made.

Pools and Pool Members: A pool is a collection of devices, often called pool members, to which the BIG-IP system passes traffic. Each pool member is defined by an IP address and a service port.

Port Translation: When an administrator needs to change the port the BIG-IP uses to communicate with backend servers, they must navigate to the specific Pool and modify the service port for each member within that pool.

Logical Separation:

Virtual Serversdefine the "front-end" port where clients connect.

Poolsdefine the "back-end" port where the application resides.

Nodesrepresent the physical server's IP address and do not contain port-specific configuration.

ASelf IPis an IP address on the BIG-IP system that you associate with a specificVLAN.

VLAN Association:A Self IP cannot exist independently; it must be bound to a VLAN to define which network segment the BIG-IP can communicate with.

Layer 2 to Layer 3 Mapping:While a VLAN is associated with physical interfaces or trunks (Layer 2), the Self IP provides the Layer 3 identity for the BIG-IP on that VLAN.

Traffic Processing:Self IPs are used by the BIG-IP for health checking backend servers, acting as a default gateway for servers, and for HA heartbeat communication.