Pass F5CAB3 Exam Guide

WAN-optimized TCP profiles improve performance for high-latency Internet clients, while LAN profiles are optimal for backend servers.

DNS traffic is primarily transported usingUDP port 53. In the exhibit, the Virtual Server is configured with theProtocol set to TCP, which prevents standard DNS queries from being processed correctly. BIG-IP Virtual Servers must be configured with the correct Layer 4 protocol to match the application traffic they are handling.

According to theBIG-IP Administration: Data Plane Configurationdocumentation:

TheProtocolsetting on a Virtual Server defines whether traffic is processed as TCP, UDP, or another supported transport protocol.

Standard DNS queries and responses useUDP, whileTCP is only required for DNS zone transfers (AXFR)or exceptionally large responses.

When a DNS Virtual Server is incorrectly configured with TCP, UDP-based DNS queries are dropped, causing all requests to fail.

Why the other options are incorrect:

A. Protocol profile (Client) to DNS_OPTIMIZEDA DNS profile enhances DNS functionality but does not correct an incorrect transport protocol configuration.

B. Type to Performance (HTTP)Performance (HTTP) Virtual Servers are designed for HTTP traffic and are not suitable for DNS services.

C. Source Address to 192.168.10.0/24The existing source IPs already fall within the allowed range, so this setting does not address the failure.

Correct Resolution:

Changing theProtocol to UDPaligns the Virtual Server with standard DNS transport requirements, allowing DNS queries to be successfully processed and load-balanced.

Slow Ramp Time prevents new pool members from receiving a full share of traffic immediately, allowing applications to warm up gradually.

Forwarding (IP) virtual servers forward traffic based on routing decisions and do not use pools or pool members.