Explanation
answer: D. CLIENT.IP.SRC IN_SUBNET(10.107.149.0/24) && (client.UDP.DSTPORT.EQ(53) || client.TCP.DSTPORT.EQ(53)) Short Explanation with reference:
An expression is a logical statement that evaluates to true or false, and can be used to match the required traffic for various purposes, such as filtering, rewriting, or load balancing. An expression can use different operators, functions, and values to specify the criteria for matching the traffic. Some of the common elements of an expression are:
CLIENT.IP.SRC: This function returns the source IP address of the client request.
IN_SUBNET: This operator checks whether an IP address belongs to a specified subnet.
&&: This operator performs a logical AND operation between two expressions.
||: This operator performs a logical OR operation between two expressions.
client.UDP.DSTPORT and client.TCP.DSTPORT: These functions return the destination port of the client request for UDP and TCP protocols, respectively.
EQ: This operator checks whether two values are equal.
In this scenario, the administrator needs to block all DNS requests from subnet 10.107.149.0/24. DNS requests are typically sent over UDP or TCP protocols, and use port 53 as the destination port. Therefore, the expression that can match this traffic is:
CLIENT.IP.SRC IN_SUBNET(10.107.149.0/24) && (client.UDP.DSTPORT.EQ(53) || client.TCP.DSTPORT.EQ(53)) This expression evaluates to true if the source IP address of the client request is in the subnet 10.107.149.0/24, and the destination port of the client request is 53 for either UDP or TCP protocol.
The other options are incorrect, as they either use the wrong function, operator, or syntax for matching the traffic. For example, option A uses the SRC function instead of the IN_SUBNET operator, which will only match a single IP address instead of a subnet. Option B uses an incorrect delimiter (space) between the subnet address and mask, which will cause a syntax error. Option C uses parentheses incorrectly, which will change the order of evaluation and result in a different meaning.
Configuring expressions | NetScaler : How to Configure an Expression to Filter Traffic - Citrix Customer Support : How to Use Operators in Expressions - Citrix Customer Support