WANs

It is great if you have an awesome network built in your small office/home office (SOHO). But unfortunately today, more than ever, many (if not most) of the resources you are going to want to access are in the cloud (Internet). This makes the wide-area network (WAN) more important than ever before. A WAN provides connectivity outside your local LAN when you need to reach resources on the Internet or another office location that is not local to you.

There are many possible WAN topologies. Let’s quickly review the most popular of them:

• ▸ Point-to-point: This simple WAN topology connects two devices over a single connection.

• ▸ Hub-and-spoke: This WAN topology features a central hub device (typically at a network HQ, for example) that makes WAN connections out to branch offices (the spokes).

• ▸ Full mesh: This WAN topology is the most expensive and complex to maintain because it has all devices making connections to all other devices. Although a full mesh can be complex and expensive, it provides excellent redundancy of WAN paths through the network.

• ▸ Single homed and dual homed: A single-homed WAN topology makes a connection to a single ISP, and a multi-homed WAN makes connections to multiple ISPs. A dual-homed configuration is very powerful because if one ISP completely fails to be able to route traffic for the customer, the customer can dynamically fail over to the surviving ISP.

Today, customers have more technological options than ever before for client connectivity to the WAN. Here is a review of the options you should know for the CCNA 200-301 exam:

• ▸ MPLS: Multiprotocol Label Switching is a data-carrying technique for high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses. This provides many advantages, including the elimination of complex lookups in a routing table. The labels identify virtual links (paths) between remote nodes rather than endpoints. MPLS can encapsulate packets of various network protocols, hence the “Multiprotocol” part of its name. MPLS supports a range of access technologies, including Ethernet, T1/E1, ATM, and DSL. Most (if not all) ISPs run MPLS internally.

• ▸ Metro Ethernet: A Metro Ethernet network is a metropolitan-area network (MAN) that is based on Ethernet standards. Such a network is commonly used to connect subscribers to a larger service network or the Internet. Businesses can also use Metro Ethernet to connect their own offices to each other. An Ethernet interface is much cheaper than a synchronous digital hierarchy (SONET/SDH) or plesiochronous digital hierarchy (PDH) interface of the same bandwidth. Another distinct advantage of an Ethernet-based access network is that it can be easily connected to the customer network due to the prevalent use of Ethernet in corporate and residential networks. Metro Ethernet service is typically implemented by ISPs using MPLS.

• ▸ Broadband PPPoE: Point-to-Point Protocol over Ethernet (PPPoE) is a network protocol for encapsulating PPP frames inside Ethernet frames. It appeared in 1999, in the context of the boom of DSL, as a solution for tunneling packets over a DSL connection to an ISP’s IP network and from there to the rest of the Internet. Typical use of PPPoE involves leveraging the PPP facilities for authenticating the user with a username and password, predominately via PAP and less often via CHAP.

• ▸ Internet VPN (DMVPN, site-to-site VPN, client VPN): Dynamic Multipoint VPN (DMVPN) is a Cisco invention for creating hub-and-spoke topologies with ease, including the dynamic creation of spoke-to-spoke tunnels in order to reduce the burdens on busy HQ (hub) devices. In the context of DMVPN, dynamic refers to VPN tunnels being established whenever required and torn down when they are not required. Site-to-site VPNs permit the creation of VPN links between locations that client devices can use to send protected data over an untrusted network (such as the Internet). Finally, client VPN software can be used to permit remote access to corporate resources. The client VPN software can be a standalone complex client app, or it can be as simple as a web browser.

SOHOs

Many of us today (I certainly do), work in SOHO environments. In fact, these networks are often filled with technology that used to be so sophisticated that it was used only in data centers. For example, my SOHO features a fiber-optic connection into my home for high-speed WAN connectivity, and it features a 10 Gbps LAN network for ultra-high speed locally. Typical SOHOs contain routers, switches, access points, firewalls, and wired and wireless endpoints.

As mentioned earlier, however, as great as a SOHO is, we are all the time needing access to more and more resources that are not within the confines of the SOHO.

On-Premises

All the IT resources (computing, storage, network) at your SOHO or enterprise network are referred to as on-premises (or on-prem) resources.

Many organizations are eager to take advantage of the many benefits of cloud technology, and more and more tools are being developed to help migrate and/or sync on-premises IT solutions with the cloud. Amazon Web Services (AWS) DataSync and the AWS Database Migration Service are just two that come to mind.

Cloud

Cloud services are incredibly popular today. From companies relying on Dropbox Business and Gmail to enterprises building their own cloud services, it seems that everyone wants to adopt some aspect of IT as a cloud service. What does it mean for IT services to really be considered cloud technology? Here is an important list of criteria:

• ▸ These services can be requested on demand from clients by using an API.

• ▸ The services offer dynamic scaling (often referred to as elasticity).

• ▸ These services rely on resource pooling in the data center.

• ▸ These services provide a wide variety of network access options.

• ▸ The use of these services can be easily measured; customers can be billed for usage according to agreements with the cloud provider. (Google Cloud Platform’s Compute Engine, for example, has a per-second billing model.)

Some larger enterprises develop their own cloud services in their own privately controlled data centers. Such a setup is known as a private cloud. In contrast, a public cloud service is one that is external to the organization. Public cloud providers (such as Google with Gmail) offer cloud services to many private enterprises and persons all over the globe.

Today, an increasing number of enterprises are using a hybrid cloud approach, in which an organization relies on private clouds for some resources and public clouds for other IT services.

Cloud technologies have given rise to the virtual service model. Here are some important examples of cloud technology as a service terms you should commit to memory:

• ▸ Infrastructure as a Service (IaaS): With IaaS, the cloud provider makes available to the customer the hardware, software, servers, storage, and other infrastructure components; IaaS providers can also host clients’ applications and handle tasks such as system maintenance, backup, and resiliency planning. Amazon Web Services (AWS) is one of the pioneers in the IaaS cloud space.

• ▸ Software as a Service (SaaS): With SaaS, the cloud provider makes powerful software available to clients. A prime example of SaaS is Gmail, through which Google provides rich email services to worldwide clients.

• ▸ Platform as a Service (PaaS): With PaaS, the cloud provider makes virtual machines (VMs) available to clients so that they can develop software applications in a test environment; it is typical for a PaaS provider to also make available software development tools as part of the platform. An example of PaaS is an AWS Drupal instance.

• ▸ X as a Service (XaaS): These days, it seems like anything and everything is being offered “as a service,” and that is exactly what XaaS (or EaaS) refers to: any aspect of IT that is delivered through the cloud model.

This list is not definitive, and there is a continuum of XaaS offerings, blurring any delineations between the above definitions, with each cloud vendor defining these terms loosely and differently.

Just as there are many virtual service offerings, there are many ways clients can connect. Remember that an aspect of cloud technologies is to enable many different network access options.

For public cloud services, most people immediately think of the Internet as the connection path. This certainly provides ease of use, convenience, and reduced costs. Unfortunately, it does come with disadvantages such as security concerns as well as quality of service issues. Virtual private network (VPN) technologies can address most security concerns, and this represents another pathing option.

Some organization might so heavily rely on cloud services that they purchase private WAN connections to these services. This permits much greater security and control, but it tends to come with higher costs. Intercloud exchanges have appeared to make these private WAN connections more affordable and flexible. Intercloud exchanges connect to multiple public cloud providers via dedicated high-speed links and make it simple for their end users to pay for only a single private connection to the exchange and then allow users to switch between the various public clouds to which the exchange is connected.

Virtual network services are becoming more and more common in making cloud-based data centers a reality. Just as the virtual machine (VM) revolutionized the computer industry, so has virtual networking changed traditional networking. More and more functions of the network are moving to virtual implementations, including the functions of the following:

• ▸ Firewalls

• ▸ Routers

• ▸ Switches

• ▸ DNS services

Virtualization of network services leads to more flexibility and more cloud-like scaling possibilities for a data center. Of course, this also leads to more programmability.