networking chapter 8
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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
• Routing Tables (cont.)– Example home router (Figure 8.7)
• 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
• Routing Tables (cont.)– Example home router (Figure 8.7)
• First Router compares destination IP address to every listing in the routing table
• Then router makes a decision
• Routing Tables (cont.)– Example home router (Figure 8.7)
• 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
• Routing Tables (cont.)– Example home router (Figure 8.7)
• 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)
• Routing Tables (cont.)– Example home router (Figure 8.7)
• 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
• 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
B. Connecting to Routers 9. Network Management Software
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
B. Connecting to Routers 9. Network Management Software
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
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