Storage, Wireless and Network Functions

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Lesson 3: Storage, wireless and functions. Welcome to lesson three. We'll finish objective 1.2: comparing networking appliances, applications and functions. Our small office from lesson two gets three upgrades. First, shared storage, with network-attached storage and storage area networks. Second, Wi-Fi, with access points and a wireless controller. And third, services that work across the network: a content delivery network, virtual private networks, quality of service, and time to live.

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NAS: file-level storage on the LAN. First, storage. The office keeps its shared files on a NAS, a network-attached storage device. A NAS is basically a file server in a box. It plugs into the normal LAN over Ethernet and offers shared folders. Clients ask for files by name and folder, using SMB on Windows or NFS on Linux and Unix. That's file-level access, and it's a simple, low-cost way to share files with everyone on the network.

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SAN: block-level storage on its own network. A storage area network, or SAN, works differently. It's a separate, high-speed network that connects servers to storage arrays. Instead of files, a SAN offers block-level storage: each server sees its slice of the array as if it were a local disk, and formats it with its own file system. SANs traditionally use Fibre Channel, or iSCSI, which carries SCSI disk commands over an ordinary IP network. Databases and virtual machine hosts are typical SAN users.

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Access point: Wi-Fi meets the wired network. Next, wireless. An access point, or AP, connects Wi-Fi devices to the wired network. It talks to laptops and phones using IEEE 802.11 radio signals, and it bridges that traffic onto Ethernet through its cable to the switch. A small office might run one or two autonomous APs, each configured on its own. That works for two, but imagine fifty access points that all need the same settings and updates.

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Wireless controller: managing many APs. That's the job of a wireless LAN controller. Lightweight access points hand their management to the controller. It configures them centrally, pushes settings and firmware updates, applies one security policy everywhere, and monitors the radios and connected clients. An open standard called CAPWAP defines one way for APs and controllers to talk. Like the appliances in lesson two, a controller can be hardware, a virtual machine, or a cloud service.

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CDN: content served from nearby. Now an application: the content delivery network, or CDN. Suppose the company's website lives on one origin server, but its customers are everywhere. A CDN copies content such as images, videos and web pages to edge servers spread around the world. Each user is sent to a nearby edge server, so pages load faster, far fewer requests reach the origin, and the site copes better with traffic spikes. Streaming services and large websites rely on CDNs.

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VPN: an encrypted tunnel. Remote workers need safe access to the office. A virtual private network, or VPN, builds an encrypted tunnel across the internet. A site-to-site VPN connects two gateways, such as a branch office and head office. It's always on, and users don't notice it. A remote access VPN connects a single device to the office gateway, usually with VPN client software on the laptop. VPNs commonly use IPsec or TLS to protect the traffic.

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QoS: who goes first. Quality of service, or QoS, decides which traffic goes first when a link is busy. Voice and video calls suffer badly from delay and jitter, while a large download can simply wait a moment. QoS classifies traffic and marks it, often with a DSCP value in the IP header, and then queues it: marked voice is sent first, and bulk traffic gets what's left. When the link isn't congested, QoS barely makes a difference.

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TTL: a limit on every packet. Finally, time to live. Every IPv4 packet carries a TTL value, set by the sender. Each router that forwards the packet subtracts one. If it reaches zero, the router discards the packet and sends an ICMP Time Exceeded message back to the sender. This stops packets from looping forever when routes go wrong. IPv6 calls the same field Hop Limit. DNS records also have a TTL: how long a cached answer stays valid.

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How the exam asks about this. On the exam, match the clue to the answer. Shared folders over the LAN, with SMB or NFS, means NAS. Block-level storage, Fibre Channel or iSCSI, means SAN. Central management of many access points is a wireless controller. Content cached on edge servers near users is a CDN. An encrypted tunnel across the internet is a VPN. Voice prioritized over downloads is QoS. And a packet discarded after too many hops points to TTL.

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Recap: storage, wireless and functions. To recap: a NAS shares files over the LAN, while a SAN gives servers block-level storage on a dedicated network. Access points connect Wi-Fi clients to the wired network, and controllers manage many APs centrally. A CDN serves content from edge servers near users. VPNs encrypt traffic across the internet, QoS puts sensitive traffic first, and TTL stops packets looping forever. Next, we'll take these ideas into the cloud.

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