Networking Chapter 8

The Wonderful World of RoutingThe Wonderful World of Routing

Chapter 8

ObjectivesObjectives• Explain how routers work• Describe dynamic routing technologies• Install and configure a router successfully

OverviewOverview

Three Parts to Chapter 8Three Parts to Chapter 8

• How Routers Work• Dynamic Routing• Working with Routers

How Routers WorkHow Routers Work

• Router– Hardware or software– Forwards packet based on destination IP

address– Layer 3, the Network layer– Classically, dedicated boxes

• At least two connections

– Popular router: CISCO 2600

Figure 8.1 Cisco 2611 router

• Home router– First exposure to a router for most techs– Connect PC to DSL receiver or cable modem– More than it appears to be– LAN side may connect internally to a built-in

switch

Figure 8.2 Business end of a typical home router

Figure 8.3 Cisco router diagram

Figure 8.4 Linksys home router diagram

• All routers– Examine packets– Send packets to proper destination

• Routing Tables– Router strips off Layer 2 information– Drops IP packet into a queue

• Source address is not important• Every packet dropped into the same queue based

on time of arrival– Router inspects the destination IP address– Router send IP packet out correct port– Routing table tells router where to send packets

Figure 8.5 Incoming packets

Figure 8.6 All incoming packets stripped of Layer 2 data and dropped into a common queue

• Routing Tables (cont.)– Example home router (Figure 8.7)

• Two ports• Each row in table defines a single route• Each column identifies specific criteria

– Destination LAN IP– Subnet Mask

• If packet’s network ID matches a Destination LAN IP, router uses other information in row to determine where to send it


• Third and fourth columns– Gateway

» IP address for the next hop router» Packet sent to Gateway if network ID does not

match one of the directly connected ports– Interface

» Tells router which port to use» “LAN” or “WAN” on sample router» Other routing tables use IP address or other info


• First Router compares destination IP address to every listing in the routing table

• Then router makes a decision


• Every router (with two exceptions) has a default route• Default route in Figure 8.7

– Destination LAN IP: 0.0.0.0– Subnet Mask: 0.0.0.0– Gateway: 76.30.4.1– Interface: WAN

• Router sends incoming packet to default route unless another line gives another route


• Destination LAN IP: 10.12.14.0 (any packet for this network)

• Subnet Mask: 255.255.255.0 (using /24 network ID)• Gateway: 0.0.0.0 (don’t use a gateway)• Interface: LAN (ARP on the LAN interface to get MAC

address and send directly to host)


• Destination LAN IP: 76.30.4.0 (any packet for this network)

• Subnet Mask: 255.255.254.0 (using /23 network ID)• Gateway: 0.0.0.0 (don’t use a gateway)• Interface: WAN (ARP on the WAN interface to get MAC

address and send directly to host)

Figure 8.7 Routing table from a home router

Figure 8.8 Electronic diagram of the router

Figure 8.9 The network based on the routing table

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• Routing Tables (cont.)– Every node on the network has a routing table

• Some computers (multi-homed) have more than one NIC

• IP uses a routing table for every packet it sends– Send directly to a host on a LAN or …– Send to the default gateway

• Routing Tables (cont.)– Computer routing table (next slide)

• More routes than example home router• Computer IP address: 10.12.14.201/24• Computer loopback: 127.0.0.1• Metric: a relative value defining the “cost” of using a

route– When more than one route to a destination,

lower metric is used– When route with lower metric goes down,

other route used

Figure 8.10 Two routes to the same network

Figure 8.11 When a route no longer works, the router automatically switches

Routing table on an XP computer connected to Figure 8.7 router

IPv4 portion of Vista route print command

• Freedom from Layer 2– Routers can connect different network

technologies– Routers strip off all Layer 2 data – Routers can connect almost anything that

stores IP packets

Figure 8.12 Modular Cisco router

Figure 8.13 Network setup

Figure 8.14 Ports at work

Figure 8.15 Redone network IDs; nodes in the LAN use private IP addressees internally

• Inside the router– Host 192.168.10.202 sends a packet to 12.43.65.223– Packet is sent to the gateway router– Router replaces the sending host’s IP with its

own public IP address– Router then adds the destination IP address

and the source ephemeral port to the NAT translation table

– On receiving response, router reverses the IP addresses and ports

Figure 8.16 NATing a packet

Figure 8.17 Updating the packet

• Inside the router (cont.)– Router compares incoming destination

port and source address to entries in NAT translation table

– Determines which local IP address to put back on the packet

– Sends packet to the correct computer on the LAN

• Port forwarding– Hides a port number from the Internet– Enables public servers to work behind a

NAT router– Gives servers the protection of NAT while

allowing access to a local server from the Internet

Dynamic RoutingDynamic Routing

A. Background1. Routers have static routes

I. Manually enteredII. Detected at setup by the router

• Background (cont.)2. Dynamic routing protocols defined

I. Routers communicate among themselves with change information

II. Update each other on changes about direct connections and distant routers

III. A passage of a packet through a single router is a hop

Figure 8.22 Lots of routers

Figure 8.23 Hopping through a WAN

Dynamic Routing Makes the Internet1. Internet depends on dynamic routing for

self-healing2. Manual updating impossible with so many

routes coming up and going down

Dynamic Routing Protocols

Protocol Type IGP(Intergateway protocol)or Notes

BGP(Border Gateway)?

RIPv1 Distance vector IGP Old; only used classful subnets

RIPv2 Distance vector IGP Supports CIDR

BGP-4 Distance vector BGP Used on the Internet, connectsAutonomous Systems

OSPF Link state IGP Fast, popular, uses Area IDs(Area 0/backbone)

IS-IS Link state IGP Alternative to OSPF

EIGRP Hybrid IGP Cisco proprietary

Table 8.1

Working with RoutersWorking with Routers

A. Simple physical installation 1. Home router

I. Give it powerII. Plug in connections

2. Business-class routerI. Insert it into a rackII. Give it powerIII. Plug in connections

B. Connecting to Routers1. Each router must be configured2. Yost cable

I. Oldest method for connecting to router for configuration

II. Almost unique to Cisco-brand routersIII. Also called rollover cable

Figure 8.39 Cisco console cable

B. Connecting to Routers3. Managed devices include both routers

and advanced switches that can be configured

4. Plug the rollover into console port on Cisco router; plug other end into serial port on a PC (may need USB-to-serial adapter)

Figure 8.40 Console port

B. Connecting to Routers5. Use a terminal emulation program to talk

to the router from the PC over this connection

I. PuTTYII. HyperTerminalIII. Serial port settings: 9600 baud, 8 data bits,

1 stop bit, no parity

Figure 8.41 Configuring PuTTY

B. Connecting to Routers 6. Once connected and running terminal

emulatorI. You will see the initial router promptII. On Cisco router, this is the Cisco IOS promptIII. Working with IOS commands

a. Type enable and press ENTERb. Prompt changes to Router#c. IOS is complexd. Newer CISCO routers will lead you through initial

configuration for basic setup

Figure 8.42 Initial router prompt

B. Connecting to Routers 7. Normally, you will access a router

through Web access or network management software (both explored next)

8. Web accessI. Most routers have a built-in Web serverII. Can do everything you need to do

B. Connecting to Routers 8. Web access

III. Easier than working with Cisco command-line IOS

IV. Web access only works if router has a built-in IP address from the factory, or you must enable Web interface after assigning an IP address to the router

V. To access the Web interface, you must know the IP address

B. Connecting to Routers 8. Web access

VI. Most techs use a laptop and a special cable (Yost or rollover or crossover) to connect directly to router for initial configurationa. Know the IP address of the routerb. Assign to the laptop an IP address with the same

network ID of the routerc. Connect to router

Figure 8.43 Default IP address

B. Connecting to Routers8. Web access

d. Check the link lights to verify proper connectione. Open the Web browser and enter the IP address

of the routerf. You will need to enter the default user name and

password (check the router’s documentation)g. Once logged in, find the settings you need

Figure 8.44 Entering the IP address

Figure 8.45 User name and password

B. Connecting to Routers9. Network Management Software

I. When managing many routers, administrators need a more advanced tool than the simple “Web-server-in-a-router”

II. Network Management Software includes utilities that will allow you to manage the entire network in a single interface (Routers, Switches, and Computers)

B. Connecting to Routers 9. Network Management Software

III. Often a Web site

IV.Administrators manage network and make necessary changes

V. Proprietary tools (OEM)a. By manufacturers of managed devices

b. Usually very powerful and easy to use

c. Only work on that OEM’s devices

Figure 8.46 Cisco Network Assistant


VI.Third-party NMS toolsa. Some free

b. Usually harder to configure

c. Must constantly be updated to work with as many devices as possible

d. Usually lack the amount of detail in an OEM NMS


VI.Third-party NMS toolse. While CiscoWorks enables you to change the

IP address of a port, third-party tools only let you see the IP settings

f. OpenNMS is a popular open-source NMS

Figure 8.47 OpenNMS

B. Connecting to Routers 10.Other connection methods

I. Most routers have more than one way to connect

II. Home router may come with a USB port and configuration softwarea. More powerful routers may allow connection

with Telnet protocol or newer Secure Shell (SSH)

B. Connecting to Routers10.Other connection methods

a. Terminal emulations protocols that look like the terminal emulators seen earlier, but that use the network rather than a serial cable

b. More on terminal emulators in Chapter 9, “TCP/IP Applications”

C. Basic Router Configuration1. Must have at least two connections2. You must properly configure every port

on a router to talk to connected network IDs

3. Make sure the routing table sends packets to where you want them to go

C. Basic Router Configuration4. STEP 1: Set up the WAN side

I. WAN side in home or small business router connects to an ISP

II. Get setup information from ISPIII. Most home routers use DHCP on the WAN

side and just need to be configured to use DHCP

C. Basic Router Configuration 4. STEP 1: Set up the WAN side

iv.May need to enter a static addressv. You can buy a single static IP addressvi. If static address, ISP will tell you what to

enter into the router

Figure 8.48 The setup

Figure 8.49 WAN router setup

C. Basic Router Configuration5. STEP 2: Set up the LAN

I. You usually have total control over the LAN side

II. Choose a network ID from the private rangeIII. Assign the correct IP information to the

LAN-side NIC

Figure 8.50 Entering a static IP

Figure 8.51 Setting up an IP address for LAN side

C. Basic Router Configuration6. STEP 3: Establish routes

I. Router will usually build a routing table based on information you provided

II. You may add more routes if neededIII. Use IOS command line on Cisco routers

C. Basic Router Configuration7. STEP 4 (Optional): Configure a Dynamic

Protocol I. Dynamic routing protocols tied to

individual NICsII. When you connect two routers together,

make sure the NICs are configured to use the same dynamic routing protocol

C. Basic Router Configuration7. STEP 4 (Optional): Configure a Dynamic

Protocol III. Unless you are in charge of two or more

routers, you will never use a dynamic routing protocol

IV. Once a dynamic routing protocol is turned on, it is all automatic

C. Basic Router Configuration8. Document and back up

I. Document what you’ve done to configure each router

II. Back up the configuration using whatever method router has

D. Router Problems1. Consider non-router issues first, because

routers don’t fail very often I. Check NICs, computer, and switches

before routerII. Routers are more reliable than other

equipment

D. Router Problems2. Keep in mind what your router is

supposed to do I. Does it just route traffic?II. Does it also perform NAT?III. Is routing failing, or is another function

of the router failing?

D. Router Problems3. Know how to use a few basic tools

that can help you check the router I. TRACEROUTE

a. Records the route between any two hostsb. Like PING, it sends out a single packet to

another hostc. Unlike PING, it returns information about

every router between them

D. Router Problems3. Know how to use a few basic tools

that can help you check the router I. TRACEROUTE

d. Tells you when things are not workinge. Gives you an idea of where to look for a problemf. Windows – TRACERTg. UNIX/Linux – TRACEROUTEh. UNIX/Linux – My TRACEROUTE (MTR)

i. Dynamic, continually updating the route

Figure 8.52 MTR in action

Networking Chapter 8

Education

gateway router router

wan router

router host

example home router

destination ip address

sample router

anat router

router hardware