WEBVTT Kind: captions Language: en 1 00:00:00.000 --> 00:00:05.272 Welcome to lesson three. We'll finish objective 1.2: comparing networking appliances, 2 00:00:05.272 --> 00:00:10.296 applications and functions. Our small office from lesson two gets three upgrades. 3 00:00:10.296 --> 00:00:15.196 First, shared storage, with network-attached storage and storage area networks. 4 00:00:15.196 --> 00:00:19.599 Second, Wi-Fi, with access points and a wireless controller. And third, 5 00:00:19.599 --> 00:00:25.305 services that work across the network: a content delivery network, virtual private networks, 6 00:00:25.305 --> 00:00:27.600 quality of service, and time to live. 7 00:00:28.000 --> 00:00:35.353 First, storage. The office keeps its shared files on a NAS, a network-attached storage device. 8 00:00:35.353 --> 00:00:42.863 A NAS is basically a file server in a box. It plugs into the normal LAN over Ethernet and offers 9 00:00:42.863 --> 00:00:50.217 shared folders. Clients ask for files by name and folder, using SMB on Windows or NFS on Linux 10 00:00:50.217 --> 00:00:57.727 and Unix. That's file-level access, and it's a simple, low-cost way to share files with everyone 11 00:00:57.727 --> 00:00:58.900 on the network. 12 00:00:59.300 --> 00:01:06.474 A storage area network, or SAN, works differently. It's a separate, high-speed network that connects 13 00:01:06.474 --> 00:01:12.070 servers to storage arrays. Instead of files, a SAN offers block-level storage: 14 00:01:12.070 --> 00:01:18.886 each server sees its slice of the array as if it were a local disk, and formats it with its own 15 00:01:18.886 --> 00:01:25.558 file system. SANs traditionally use Fibre Channel, or iSCSI, which carries SCSI disk commands 16 00:01:25.558 --> 00:01:31.800 over an ordinary IP network. Databases and virtual machine hosts are typical SAN users. 17 00:01:32.200 --> 00:01:38.585 Next, wireless. An access point, or AP, connects Wi-Fi devices to the wired network. 18 00:01:38.585 --> 00:01:45.882 It talks to laptops and phones using IEEE 802.11 radio signals, and it bridges that traffic onto 19 00:01:45.882 --> 00:01:52.951 Ethernet through its cable to the switch. A small office might run one or two autonomous APs, 20 00:01:52.951 --> 00:02:00.020 each configured on its own. That works for two, but imagine fifty access points that all need 21 00:02:00.020 --> 00:02:02.300 the same settings and updates. 22 00:02:02.700 --> 00:02:09.126 That's the job of a wireless LAN controller. Lightweight access points hand their management to 23 00:02:09.126 --> 00:02:14.740 the controller. It configures them centrally, pushes settings and firmware updates, 24 00:02:14.740 --> 00:02:20.557 applies one security policy everywhere, and monitors the radios and connected clients. 25 00:02:20.557 --> 00:02:25.901 An open standard called CAPWAP defines one way for APs and controllers to talk. 26 00:02:25.901 --> 00:02:31.515 Like the appliances in lesson two, a controller can be hardware, a virtual machine, 27 00:02:31.515 --> 00:02:32.800 or a cloud service. 28 00:02:33.200 --> 00:02:39.992 Now an application: the content delivery network, or CDN. Suppose the company's website lives 29 00:02:39.992 --> 00:02:46.711 on one origin server, but its customers are everywhere. A CDN copies content such as images, 30 00:02:46.711 --> 00:02:53.722 videos and web pages to edge servers spread around the world. Each user is sent to a nearby edge 31 00:02:53.722 --> 00:03:00.807 server, so pages load faster, far fewer requests reach the origin, and the site copes better with 32 00:03:00.807 --> 00:03:05.700 traffic spikes. Streaming services and large websites rely on CDNs. 33 00:03:06.100 --> 00:03:11.514 Remote workers need safe access to the office. A virtual private network, 34 00:03:11.514 --> 00:03:18.709 or VPN, builds an encrypted tunnel across the internet. A site-to-site VPN connects two gateways, 35 00:03:18.709 --> 00:03:24.865 such as a branch office and head office. It's always on, and users don't notice it. 36 00:03:24.865 --> 00:03:32.282 A remote access VPN connects a single device to the office gateway, usually with VPN client software 37 00:03:32.282 --> 00:03:37.400 on the laptop. VPNs commonly use IPsec or TLS to protect the traffic. 38 00:03:37.800 --> 00:03:44.093 Quality of service, or QoS, decides which traffic goes first when a link is busy. 39 00:03:44.093 --> 00:03:51.552 Voice and video calls suffer badly from delay and jitter, while a large download can simply wait 40 00:03:51.552 --> 00:03:58.389 a moment. QoS classifies traffic and marks it, often with a DSCP value in the IP header, 41 00:03:58.389 --> 00:04:04.761 and then queues it: marked voice is sent first, and bulk traffic gets what's left. 42 00:04:04.761 --> 00:04:09.500 When the link isn't congested, QoS barely makes a difference. 43 00:04:09.900 --> 00:04:16.083 Finally, time to live. Every IPv4 packet carries a TTL value, set by the sender. 44 00:04:16.083 --> 00:04:21.570 Each router that forwards the packet subtracts one. If it reaches zero, 45 00:04:21.570 --> 00:04:28.525 the router discards the packet and sends an ICMP Time Exceeded message back to the sender. 46 00:04:28.525 --> 00:04:36.099 This stops packets from looping forever when routes go wrong. IPv6 calls the same field Hop Limit. 47 00:04:36.099 --> 00:04:41.200 DNS records also have a TTL: how long a cached answer stays valid. 48 00:04:41.600 --> 00:04:46.984 On the exam, match the clue to the answer. Shared folders over the LAN, 49 00:04:46.984 --> 00:04:52.445 with SMB or NFS, means NAS. Block-level storage, Fibre Channel or iSCSI, 50 00:04:52.445 --> 00:04:58.284 means SAN. Central management of many access points is a wireless controller. 51 00:04:58.284 --> 00:05:05.413 Content cached on edge servers near users is a CDN. An encrypted tunnel across the internet is 52 00:05:05.413 --> 00:05:12.769 a VPN. Voice prioritized over downloads is QoS. And a packet discarded after too many hops points 53 00:05:12.769 --> 00:05:13.569 to TTL. 54 00:05:13.700 --> 00:05:20.276 To recap: a NAS shares files over the LAN, while a SAN gives servers block-level storage on a 55 00:05:20.276 --> 00:05:25.651 dedicated network. Access points connect Wi-Fi clients to the wired network, 56 00:05:25.651 --> 00:05:32.227 and controllers manage many APs centrally. A CDN serves content from edge servers near users. 57 00:05:32.227 --> 00:05:37.531 VPNs encrypt traffic across the internet, QoS puts sensitive traffic first, 58 00:05:37.531 --> 00:05:43.400 and TTL stops packets looping forever. Next, we'll take these ideas into the cloud.