Router Basics MM Clements

Introduction WAN introduction and devices MODEM technologies Router Functions Router Hardware Connecting to a router for the first time 4/26/2017 ITCN

Router Function Linking WANs and LANs Interconnecting communication lines Path determination and packet switching Application of security rules (ACLs) Protocol conversion (encapsulation) E.g. HDLC, PPP etc. 4/26/2017 ITCN

Introduction to WANs A wide area network (WAN) is a data communications network spanning a large geographic area such as a region, country or the entire planet A WAN may interconnect LANs May use microwave, satellite, fibre-optic, phone lines etc. to cover distances 4/26/2017 ITCN

WAN Devices Switch connects PCs, servers etc. to a router Ethernet cannot travel large distances so MODEM is used MODEM terminates a data circuit – data circuit-terminating equipment (DCE) Communication server allows many users access to a MODEM link 4/26/2017 ITCN

Use of MODEM in WANs MODEM = Modulator and Demodulator Translates between Ethernet and WAN technology and back again Permits long distance communications 4/26/2017 ITCN

Routers Connected by WAN Technologies 4/26/2017 ITCN

Some WAN Terminologies T1=1.544 Mbps, T3=44.736 Mbps , X.25, SMDS (SWITCHED MULTIMEGABIT DATA SERVICE), ATM, xDSL, Modem, Cable Modem, ISDN, OC-x X.25 and ISDN are used less today than in the past but can still be found in operation 4/26/2017 ITCN

Cisco Routers Operating system is known as Internetwork Operating System (IOS) Held in Flash memory (non-volatile) CLI not GUI Based on UNIX heritage 4/26/2017 ITCN

Router Operation Layer 3 device Accepts PDUs on incoming network Examines PDU data Makes decision(s) for next stage of PDU journey May modify PDU contents (not payload) Passes PDU on to outgoing network 4/26/2017 ITCN

Router Sorts Incoming Traffic Acts like Internet roundabout Allows data to get closer to its destination Best path decision made by router Incoming packets are switched to the most appropriate outgoing network 4/26/2017 ITCN

Data Link Layer and Routing Router does not pass on layer 2 data e.g. broadcasts do not pass router Layer 2 header is modified by router Source and destination MAC addresses are changed at each router 4/26/2017 ITCN

Network Path Determination Router accepts packet and views inside Network Layer header IP address of destination carried in Network Layer header and other information Destination IP address looked up in routing table Packet passed to appropriate exit interface 4/26/2017 ITCN

Transport Layer Determination Transport Layer header contents examined Source and destination port checked May trigger security of an Access Control List May drop packets under heavy load UDP often first casualty 4/26/2017 ITCN

Access Control Lists Used to identify incoming packets Can be used for security purposes E.g. do not allow TELNET traffic Identified by destination port number 23 Found in Transport Layer header More on ACLs later in course 4/26/2017 ITCN

Inside a Router Router is a dedicated computer Contains hardware found in most PCs Does not have hard disk – Flash memory is used instead to hold IOS NVRAM used to hold configuration files DRAM used to hold routing tables, buffering, ARP cache etc CPU, ROM and interfaces too 4/26/2017 ITCN

Internal Components of a 2600 Router 4/26/2017 ITCN

External Connections Configuration connections LAN connections Console and AUX LAN connections FastEthernet (usually) WAN connections – often via WAN Interface Cards (WICs) Newer hardware is modular Makes upgrading cheaper 4/26/2017 ITCN

External Connections on a Router 4/26/2017 ITCN

Router Connections 4/26/2017 ITCN

9600 baud 8 data bits 1 stop bit No parity No flow control Connecting to a Router First-time connection must be via console cable attached to a PC PC runs terminal emulator e.g. Hyperterminal Correct parameters must be set 9600 baud  8 data bits  1 stop bit  No parity  No flow control 4/26/2017 ITCN

Physical Connection to Router 4/26/2017 ITCN

Conclusion Routers choose paths and switch data packets IOS runs on Cisco hardware Apply security etc. No hard disk – all solid state New routers have modular chassis for flexibility Terminal emulator and rollover cable to connect 4/26/2017 ITCN