Sunday, January 21, 2018

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Routers and Routing Basics - WANs and Routers

WAN? Never heard of it…

• Provides long-distance connections at a lower data ratebetween networking devices across a large geographical area.

– ... unlike LANs, which generally connect end-user devices (eg. workstations, printers) across a small area (eg. a building).

• Usually long-distance links owned and operated by telcos, and leased out to customers.

– American WAN providers include Regional Bell Operating Companies (RBOCs), AT&T (formerly SBC and BellSouth), Sprint, Verizon, Qwest, and MCI (formerly WorldCom).

– Australian WAN providers include Telstra, SingTel Optus, Macquarie Telecom, Soul, AAPT, PowerTel, and TransACT.

• The Internet is a collection of WANs.

More on WANs

• Devices in a WAN include:

– Routers

– Modems (including CSU/DSUs and TA/NT1s)

– Communications servers

• WAN physical layer describes the connectionbetween DTE and DCE, implemented by standards such as E1, E3, xDSL, and SONET.

• WAN data link layer protocolsinclude HDLC, PPP, Frame Relay, ISDN, ATM, SLIP, and SDLC.

Router? Don’t know that too…

• Routers use routing tables to determine the most efficient pathfor packets to take to their destination.

• Determines next hop for incoming packets to take–based on directly connected subnets; or routing protocols

• WAN technologies are frequently used to connect routers.

• A major role for routers in WANs is to provide connections betweensubnets; and various WAN links

What’s in the box?

• RAM (Random Access Memory)

– Stores routing tables and ARP cache.

– Run time space for Cisco IOS (Internetwork Operating System) to load and execute, and for temporary router configuration files to be stored.

• NVRAM (Non-Volatile RAM)

– Stores router initialisation configuration files.

– Unlike RAM, NVRAM doesn’t lose contents when powered down.

• Flash Memory

– Stores Cisco IOS software images, allows for software upgrades ‘on the fly’.

– Retains contents when powered down.

• ROM (Read Only Memory)

– Stores the hardware diagnostics code that runs upon startup.

– Copies Cisco IOS from Flash memory to RAM.

– Permanent, non-erasable form of memory.

Get plugged in to routers

• Management asynchronous serial lines are primarily used for router configuration purposes.

• LAN and WAN interfaces connect routers to networks to accept and redirect packets.

How to console a router…

• Use management ports to configure a router:

– Console ports require a rollover cableto connect to the serial port of a host running terminal emulation software, eg. HyperTerm

– AUX ports are connected to a modem used for other hosts to dial-in to, to establish a remote connection.

Routers in LANs and WANs

• LAN Interfaces

– Usually Fast Ethernet over Cat5 (or higher grade) UTP.

– Can also be Token Ring, or Gigabit Ethernet over fibre.

• WAN Interfaces

– Serial and ISDN technologies across leased line, circuit-switched, and packet-switched connections.

– A variety of physical connectors are used for WAN links.

• Most common is serial link between DTE and DCE devices.


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