the header of a received packet 1 the NGFW needs to check the packets flow and

The header of a received packet 1 the ngfw needs to

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the header of a received packet (1), the NGFW needs to check the packet’s flow and / or session membership (3, 6, 8). Furthermore, a scan of the packet’s payload might be necessary (4) before deciding whether to forward, redirect, or drop the packet (7). Finally, packet headers need to be rewritten (2), sometimes also with payload modification (5) e.g., in the case of proxying or for encryption in the case of VPN tunneling. B. Virtualization Techniques In order to fully reap the flexibility and scalability benefits of the NFV paradigm, the underlying infrastructure needs to expose access to a shared resource pool. Simultaneously, it needs to maintain isolation between different tenants and dynamically adapt the resource allocation to VNF instances for scalability and efficiency. In this context, conventional host resources such as compute, memory, and storage are virtualized alongside networking resources, i.e., links between nodes with delay and bandwidth guarantees. In the following, we provide an overview of virtualization mechanisms from these two categories and refer to them as (1) hardware and (2) network virtualization, respectively. The choice of options from these two categories results in different trade-offs regard- ing costs, performance, and flexibility. 1) Hardware Virtualization.: The main goal in the context of hardware virtualization consist of providing a functional equivalent of the original hardware to the VNF while limiting performance degradation. This is achieved by the virtualization layer that resides between the physical and virtualized in- frastructure. Options regarding its implementation range from different hypervisors to container-based approaches which offer different degrees of resource and isolation, security, and performance [ 2 ], [ 12 ]. Hypervisors can reside at different locations in the system. On the one hand, hypervisors such as Xen [ 13 ] and ESXi [ 14 ] run directly on the physical machine and directly handle hardware access as well as interrupts. On the other hand,
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5 hypervisors like KVM [ 15 ] require the presence of kernel modules in the host OS and kernel processes are responsi- ble for handling events and interrupts. Due to the different numbers of intermediate abstraction layers, implementation details, and the heterogeneity of possible use cases, there is no single hypervisor that performs best in all scenarios and therefore should be chosen carefully to match the particular requirements [ 16 ]. Furthermore, high-speed I/O virtualization plays a crucial role for meeting performance requirements and maximizing flexibility when VNFs are run inside VMs [ 17 ]. To this end, drivers such as virtio [ 18 ] and ptnet [ 19 ] provide a common device model for accessing virtual interfaces. Recently, container-based technologies like Docker [ 20 ] have gained popularity, that instead share the kernel of the host OS and provide isolation through segregated process namespace (anciently known as BSD jails [ 21 ]). On the one hand, containers avoid the overhead of providing an entire guest OS, enabling a flexible and lightweight deployment. In
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