Overlay Networks

Correct Answer: Increased number of virtual networks

The main advantage of using VXLANs in a multi-tenant virtualized data center is the 'Increased number of virtual networks'. This is because VXLANs can support up to 16 million separate Layer 2 networks compared to the 4096 VLANs limit. This feature makes it the perfect solution for large-scale cloud data center deployment. On the other hand, 'Decreased MTU size' is not an advantage, as VXLANs actually increase the MTU size because of added encapsulation. 'Simplified layer 2 configurations' is a somewhat valid point, but it's not the primary advantage. And, 'Reduced broadcast domain size' is also not an advantage, as VXLANs are designed to extend Layer 2 segments over Layer 3 networks, not to reduce broadcast domains.

Correct Answer: Encapsulate non-IP packets to be transmitted over an IP network

A Generic Routing Encapsulation (GRE) tunnel is a communication protocol developed by Cisco Systems, mainly used to encapsulate a wide variety of network layer protocols inside virtual point-to-point links or point-to-multipoint links over an Internet Protocol network. This means that its primary purpose is to enable the encapsulation of non-IP packets so that they can be transmitted over an IP network - which is precisely what the first answer points out. The other three choices provided do not accurately describe the main purpose of a GRE tunnel. Data compression, for instance, is not a function carried out by a GRE tunnel. Instead, this task is generally performed by other protocols within the network stack. QoS, or Quality of Service, refers to the ability to provide different priorities to different types of data, and although it can be applied within a GRE tunnel, it's not the primary purpose of such a tunnel. Finally, encryption of data is not inherently provided within a GRE tunnel - encryption is typically applied on a GRE tunnel through the use of IPsec, which is another protocol entirely. Thus, among the options given, the statement 'Encapsulate non-IP packets to be transmitted over an IP network' is the correct answer.

Correct Answer: Abstraction of physical infrastructure

The feature that best describes an overlay network's ability to facilitate communication between disparate virtual resources is the 'Abstraction of physical infrastructure'. An overlay network is designed to create a virtual network that is abstracted from the underlying physical network infrastructure. This allows for greater flexibility and the ability to connect virtual resources that may be spread across different physical locations or across multiple underlying networks, without being limited by the physical network's topology or configuration. The other options are less accurate: 'Replication of underlying physical network topology' is incorrect because an overlay network does not need to replicate the physical topology; it is abstract and independent of it. 'Direct translation of virtual to physical addresses' is not the principal feature of an overlay network; while address translation may occur, it's not the defining capability. Finally, 'Extension of the existing physical network perimeter' is also incorrect, as overlay networks create their own logical network that extends beyond the physical network perimeter without necessarily changing the physical network itself.