Chapter 1
Introduction to Routing and
Packet Forwarding
CIS 82 Routing Protocols and Concepts
Rick Graziani
Cabrillo College
graziani@cabrillo.edu
Last Updated: 2/16/2009
This Presentation
 For detailed information see the notes section within this
PowerPoint.
 This presentation is based on the Exploration course/book, Routing
Protocols and Concepts.
 For a copy of this presentation and access to my web site for other
CCNA, CCNP, and Wireless resources please email me for a
username and password.
 Email: graziani@cabrillo.edu
 Web Site: www.cabrillo.edu/~rgraziani
2
Note
 This chapter contains mostly introductory material.
 Most of not all of this information will be explained in more detail
in later chapters or later courses.
 The bootup process and the IOS are examined in a later
course.
 Do not worry or focus too much on the details for now.
 This will all be examined and explained in the following chapters.
3
For further information
 This presentation is an
overview of what is
covered in the
curriculum/book.
 For further explanation
and details, please read
the chapter/curriculum.
 Book:
 Routing Protocols
and Concepts
 By Rick Graziani and
Allan Johnson
 ISBN: 1-58713-206-0
 ISBN-13: 978-58713206-3
4
Topics


Inside the Router
 Routers are computers
 Router CPU and Memory
 Internetwork Operating
System
 Router Bootup Process
 Router Ports and Interfaces
 Routers and the Network
Layer
Path Determination and
Switching Function
 Packet Fields and Frame
Formats
 Best Path and Metrics
 Equal Cost Load Balancing
 Path Determination
 Switching Function


CLI Configuration and
Addressing
 Implementing Basic
Addressing Schemes
 Basic Router
Configuration
Building the Routing Table
 Introducing the Routing
Table
 Directly Connected
Networks
 Static Routing
 Dynamic Routing
 Routing Table Principles
5
Inside the Router
 Routers are computers
 Router CPU and Memory
 Internetwork Operating System
 Router Bootup Process
 Router Ports and Interfaces
 Routers and the Network Layer
Routers are Computers
Leonard Kleinrock and the first IMP.
 A router is a computer:
 CPU, RAM, ROM, Operating System
 The first router: used for the Advanced Research Projects Agency
Network (ARPANET):
 IMP (Interface Message Processor)
 Honeywell 516 minicomputer that brought the ARPANET to life
on August 30, 1969.
7
 Routers forwarding packets (packet switching):
 From the original source to the final destination.
 Selects best path based on destination IP address
 A router connects multiple networks:
 Interfaces on different IP networks
8
 Router interfaces:
 LAN
 WAN
9
Routers Determine the Best Path
 The router’s primary responsibility:
 Determining the best path
 Forwarding packets toward their destination
10
Routers Determine the Best Path
IP Packet enters router’s Ethernet interface.
Router examines the packet’s destination IP address.
Router searches for a best match between packet’s destination IP address and
network address in routing table.
Using the exit-interface in the route, the packet is forwarded to the next router or
the final destination.
 Routing table
 Determines best path.
 Best match between destination IP address and network
address in routing table
11
Router
CPU and
Memory
 CPU - Executes operating system instructions
 Random access memory (RAM)
 running copy of configuration file
 routing table
 ARP cache
 Read-only memory (ROM)
 Diagnostic software used when router is powered up.
 Router’s bootstrap program
 Scaled down version of operating system IOS
 Non-volatile RAM (NVRAM)
 Stores startup configuration. (including IP addresses, Routing protocol)
 Flash memory - Contains the operating system (Cisco IOS)
 Interfaces - There exist multiple physical interfaces that are used to connect
network. Examples of interface types:
 Ethernet / fast Ethernet interfaces
 Serial interfaces
 Management interfaces
12
Router physical characteristics
13
Cisco IOS - Internetwork
Operating System
 Responsible for managing the hardware and software resources:
 Allocating memory
 Managing processes
 Security
 Managing file systems
 Many different IOS images.
 An IOS image is a file that contains the entire IOS for that router.
 Router model
 IOS features
 Example IPv6 or a routing protocol such as Intermediate System–
to–Intermediate System (IS-IS).
14
Router Bootup Process (more in later course)
15
Bootup Process
running-config
IOS (running)
startup-config
IOS
Bootup program
ios (partial)
16
Where is the permanent configuration file stored used during boot-up?
NVRAM
Where is the diagnostics software stored executed by hardware modules? ROM
Where is the backup (partial) copy of the IOS stored?
ROM
Where is IOS permanently stored before it is copied into RAM?
FLASH
Where are the bootsystem commands stored which are used to locate
the IOS?
NVRAM
running-config
IOS (running)
startup-config
IOS
Bootup program
ios (partial)
17
?
?
?
?
?
?
?
running-config
IOS (running)
startup-config
IOS
Bootup program
ios (partial)
18
startup-config
IOS
running-config
IOS (running)
running-config
IOS (running)
ios (partial)
startup-config
Bootup program
IOS
Bootup program
ios (partial)
19
Router Boot Process –
Details (later)
1. ROM
1. POST
2. Bootstrap code executed
3. Check Configuration Register value (NVRAM)
0 = ROM Monitor mode
1 = ROM IOS
2 - 15 = startup-config in NVRAM
2. Check for IOS boot system commands in startup-config file (NVRAM)
If boot system commands in startup-config
a. Run boot system commands in order they appear in startup-config to locate the IOS
b If boot system commands fail, use default fallback sequence to locate the IOS (Flash, TFTP, ROM)
3. Locate and load IOS, Default fallback sequence: No IOS boot system commands in startup-config
a. Flash (sequential)
b. TFTP server (netboot) - The router uses the configuration register value to form a filename from
which to boot a default system image stored on a network server.
c. ROM (partial IOS) or keep retrying TFTP depending upon router model
- If no IOS located, get partial IOS version from ROM
4. Locate and load startup-config configuration
a. If startup-config found, copy to running-config
b. If startup-config not found, prompt for setup-mode
c. If setup-mode bypassed, create a “skeleton” default running-config (no startup-config)
20
Verify the router boot-up process
 show version command is used to view information about the
router during the bootup process (later).
21
Ports and Interfaces
 Port - normally means one of the management ports used for
administrative access
 Interface normally refers to interfaces that are capable of sending
and receiving user traffic.
 Note: However, these terms are often used interchangeably in the
industry and even with IOS output.
22
Management
Ports
Console port
 Terminal
 PC running terminal emulator software
 No need for network access
 Used for initial configuration
Auxiliary (AUX) port
 Not all routers have auxiliary ports.
 At times, can be used similarly to a console port
 Can also be used to attach a modem.
 Note: Auxiliary ports will not be used in this curriculum.
23
Router Interfaces
 Interfaces - Receive and forward packets.
 Various types of networks
 Different types of media and connectors.
 Different types of interfaces.
 Fast Ethernet interfaces - LANs
 Serial interfaces - WAN connections including T1, DSL, and ISDN
24
Router Interfaces
FastEthernet 0/0
MAC: 0c00-41cc-ae12
10.1.0.1/16
FastEthernet 0/0
MAC: 0c00-3a44-190a
192.168.1.1/24
Serial 0/0
172.16.1.1/24
Serial 0/1
172.16.1.2/24
 Router Interface:
 Different network
 IP address and subnet mask of that network
 Cisco IOS will not allow two active interfaces on the same
router to belong to the same network.
25
LAN Interfaces
 Ethernet and Fast Ethernet interfaces
 Connects the router to the LAN
 Layer 2 MAC address
 Participates in the Ethernet
 Address Resolution Protocol (ARP):
 Maintains ARP cache for that interface
 Sends ARP requests when needed
 Responds with ARP replies when required
 Typically an RJ-45 jack (UTP).
 Router to switch: straight-through cable
 Router to router: crossover cable
26
WAN Interfaces
 Point-to-Point, ISDN, and Frame Relay interfaces
 Connects routers to external networks.
 The Layer 2 encapsulation can be different types including:
 PPP
 Frame Relay
 HDLC (High-Level Data Link Control).
 Note: MAC addresses are used only on Ethernet interfaces and are
not on WAN interfaces.
 Layer 2 WAN encapsulation types and addresses are covered in a
later course.
27
Routers at
the
Network
Layer
 Layer 3 device because its primary forwarding
decision is based on the information in the Layer 3 IP
packet (destination IP address).
 This is known as routing.
28
Routers Operate at Layers 1, 2, and 3
29
Path Determination and
Switching Functions
 Packet Fields and Frame Formats
 Best Path and Metrics
 Equal Cost Load Balancing
 Path Determination
 Switching Function
Path Determination and Switching Functions
 The following sections focus on exactly what happens to data as it
moves from source to destination.
 Review the packet and frame field specifications
 Discuss in detail how the frame fields change from hop to hop,
whereas the packet fields remain unchanged
31
Ethernet Frame
IPv4 (Internet
Protocol)
 Layer 2 addresses:
 Interface-to-Interface on the same network.
 Changes as packet is decapsulated and encapsulated from
network to network
 Layer 3 addresses:
 Original source layer 3 address (IP)
 Final destination layer 3 address (IP)
 Does not change (except with NAT, but this is not a concern of IP
but an internal network process)
32
Best Path
 Router’s best-path to a network:
 optimum or “shortest” path
 Routing protocol dependent
 Dynamic routing protocols use their own rules and metrics.
 A metric is the quantitative value used to measure the distance to a
given route.
 The best path to a network is the path with the lowest metric.
 Example, a router will prefer a path that is one hop away over a path
that is two hops away.
33
Best Path
1.5 Mbps
1.5 Mbps
 Comparing Dynamic Routing Protocols: RIP and OSPF
 RIP uses hop count
 R1 to R3
 Fewer links but much slower
 OSPF uses bandwidth
 R1 to R2 to R3
 More routers but much faster links
34
To reach the 192.168.1.0/24
network it is 2 hops via R2 and 2
hops via R4.
Equal Cost
Load
Balancing
?
?
192.168.1.0/24
What happens if a routing table has two or
more paths with the same metric to the same
destination network? (equal-cost metric)
Router will perform equal-cost load balancing.
35
Equal-Cost Paths
Versus UnequalCost Paths
T1
T3
192.168.1.0/24
Can a router use multiple paths if the paths
(cost, metric) to reach the destination
network are not equal?
Yes, if the routers are using the EIGRP routing
protocol which supports unequal cost load
balancing.
36
Path Forwarding
 Packet forwarding involves two functions:
 Path determination function
 Switching function
37
Path Forwarding
Router receives packet.
Destination IP address matches a network on one
of its directly connected networks.
Packet is forwarded out
that network.
Directly connected
network
 Path determination function is the process of how the router determines
which path to use when forwarding a packet.
 To determine the best path, the router searches its routing table for a
network address that matches the packet’s destination IP address.
 One of three path determinations results from this search:
 Directly connected network
 Remote network
 No route determined
38
Path Forwarding
Router receives packet.
Destination IP address matches a remote network
which can only be reached via another router.
Packet is forwarded out that
network to the next-hop router.
Remote
network
 Path determination function is the process of how the router determines
which path to use when forwarding a packet.
 To determine the best path, the router searches its routing table for a
network address that matches the packet’s destination IP address.
 One of three path determinations results from this search:
 Directly connected network
 Remote network
 No route determined
39
Path Forwarding
Router receives packet.
Destination IP address does NOT match any
network in the router’s routing table.
Packet is dropped.
No route
determined
Does
this mean the network does not
 Path determination function is the process of how the router determines
exist?
which path to use when forwarding a packet.
 To determine the best path, the router searches its routing table for a
No,
only address
that the
does
not know
network
thatrouter
matches
the packet’s
destination IP address.
(later) results from this search:
about
One ofthat
threenetwork.
path determinations
 Directly connected network
 Remote network
 No route determined
40
Path Forwarding
 Switching function is the process used by a router to:
 Accept a packet on one interface and
 Forward it out another interface
 A key responsibility of the switching function is to encapsulate
packets in the appropriate data-link frame type for the outgoing data
link.
41
192.168.4.10
Path
Forwarding
192.168.1.10
Layer 2 Data Link Frame
Dest. MAC
0B-31
00-10
Source MAC
00-20
0A-10
Layer 3 IP Packet
Type
800
Dest. IP
192.168.4.10
Source IP
192.168.1.10
IP
fields
Data
Trailer
What does a router do with a packet received from one network and destined for another
network?
1. Decapsulates the Layer 3 packet by removing the Layer 2 frame header and trailer
2. Examines the destination IP address of the IP packet to find the best path in the
routing table
3. Encapsulates the Layer 3 packet into a new Layer 2 frame and forwards the frame
out the exit interface
42
Remember: Encapsulation
These addresses
do not change!
Layer 3 IP Packet
These change from
host to router, router to
router, and router to
host.
Destination IP
Address
Source IP
Address
Other IP
fields
Data
Layer 2 Data Link Frame
Destination
Address
Next hop Data
Link Address of
Host or Router’s
interface

Source
Address
Type
Data
Trailer
Current Data Link
Address of Host or
Router’s exit interface
Now, let’s do an example…
43
Layer 2 Data Link Frame
Dest.
Dest.Add
MAC
MAC
0B-31
FF-FF
00-10
Source Add
MAC
0A-10
00-20
Layer 3 IP Packet
Type
800
Dest. IP
192.168.4.10
Source IP
192.168.1.10
IP
fields
Data
Trailer
 This is just a summary.
 The details will be shown next!
 Now for the details…
44
Layer 2 Data Link Frame
Dest. MAC
00-10
Source MAC
0A-10
Layer 3 IP Packet
Type
800
Dest. IP
192.168.4.10
Source IP
192.168.1.10
IP
fields
Data
Trailer
From Host X to Router RTA
 Host X begins by encapsulating the IP packet into a data link frame (in this
case Ethernet) with RTA’s Ethernet 0 interface’s MAC address as the data
link destination address.
 How does Host X know to forward to packet to RTA and not directly to Host
Y?
 IP Source and IP Destination Addresses are on different networks
 How does Host X know or get RTA’s Ethernet address?
 Checks ARP Table for Default Gateway IP Address and associated
MAC Address.
 What if it there is not an entry in the ARP Table?
 Host X sends an ARP Request and RTA sends an ARP Reply
45
Layer 2 Data Link Frame
Dest. MAC
0B-31
00-10
Source
Source MAC
MAC
00-20
0A-10
Layer 3 IP Packet
Type
Type
800
800
RTA ARP Cache
IP Address
MAC Address
192.168.2.2
0B-31
Dest. IP
192.168.4.10
Source IP
192.168.1.10
Network
192.168.1.0/24
192.168.2.0/24
192.168.3.0/24
192.168.4.0/24
IP
fields
Data
Trailer
Trailer
RTA Routing Table
Hops Next-hop-ip Exit-interface
0
Dir.Conn.
e0
0
Dir.Conn
e1
1
192.168.2.2
e1
2
192.168.2.2
e1
RTA
1. RTA examines Destination MAC address, which matches the E0 MAC address, so it copies in the frame.
2. RTA sees the Type field is 0x800, IP packet in the data field, a packet which needs to be routed.
3. RTA strips off the Ethernet frame.
RTA looks up the Destination IP Address in its routing table.
 192.168.4.0/24 has next-hop-ip address of 192.168.2.2 and an exit-interface of e1.
 Since the exit interface is on an Ethernet network, RTA must resolve the next-hop-ip address with a
destination MAC address.
4. RTA looks up the next-hop-ip address of 192.168.2.2 in its ARP cache.
 If the entry was not in the ARP cache, the RTA would need to send an ARP request out e1. RTB
would send back an ARP reply, so RTA can update its ARP cache with an entry for 192.168.2.2. 5.
Packet is encapsulated into a new data link (Ethernet) frame.
46
Layer 2 Data Link Frame
Dest. Add
MAC
FF-FF
0B-31
Source Add
MAC
00-20
Layer 3 IP Packet
Type
800
Dest. IP
192.168.4.10
Source IP
192.168.1.10
Network
192.168.1.0/24
192.168.2.0/24
192.168.3.0/24
192.168.4.0/24
IP
fields
Data
Trailer
RTB Routing Table
Hops Next-hop-ip Exit-interface
1
192.168.2.1
e0
0
Dir.Conn
e0
0
Dir.Conn
s0
1
192.168.3.2
s0
RTB
1. RTB examines Destination MAC address, which matches the E0 MAC address, and copies in the frame.
2. RTB sees Type field, 0x800, IP packet in the data field, a packet which needs to be routed.
3. RTB strips off the Ethernet frame.
RTB looks up the Destination IP Address in its routing table.
 192.168.4.0/24 has next-hop-ip address of 192.168.3.2 and an exit-interface of Serial0.
 Since the exit interface is not an Ethernet network, RTB does not have to resolve the next-hop-ip address
with a destination MAC address.
 When the interface is a point-to-point serial connection, (like a pipe), RTB encapsulates the IP packet into
the proper data link frame, using the proper serial encapsulation (HDLC, PPP, etc.).
 The data link destination address is set to a broadcast (there’s only one other end of the pipe).
5. Packet is encapsulated into a new data link (serial, PPP) frame and sent out the link.
47
Layer 2 Data Link Frame
Dest.
Dest.Add
MAC
FF-FF
0B-20
Source
SourceAdd
MAC
0C-22
Layer 3 IP Packet
Type
Type
800
800
RTC ARP Cache
IP Address
MAC Address
192.168.4.10
0B-20
Dest. IP
192.168.4.10
Source IP
192.168.1.10
IP
fields
Data
Trailer
RTC Routing Table
Network
Hops Next-hop-ip Exit-interface
192.168.1.0/24 2
192.168.3.1
s0
192.168.2.0/24 1
192.168.3.1
s0
192.168.3.0/24 0
Dir.Conn
s0
192.168.4.0/24 0
Dir.Conn
e0
RTC
1. RTC copies in the data link (serial, PPP) frame.
2. RTC sees the Type field is 0x800, IP packet in the data field, a packet which needs to be routed.
3. RTC strips off the data link, serial, frame.
RTC looks up the Destination IP Address in its routing table.

RTC realizes that this Destination IP Address is on the same network as one of its interfaces and it can sent the packet
directly to the destination and not another router.

Since the exit interface is on an directly connected Ethernet network, RTC must resolve the destination ip address with
a destination MAC address.
2. RTC looks up the destination ip address of 192.168.4.10 in its ARP cache.

If the entry was not in the ARP cache, the RTC would need to send an ARP request out e0. Host Y would send back an
ARP reply, so RTC can update its ARP cache with an entry for 192.168.4.10.
5. Packet is encapsulated into a new data link (Ethernet) frame and sent out the interface.
48
Layer 2 Data Link Frame
Dest. MAC
0B-20
Source MAC
0C-22
Layer 3 IP Packet
Type
800
Dest. IP
192.168.4.10
Source IP
192.168.1.10
IP
fields
Data
Trailer
Host Y
Layer 2: Data Link Frame
1. Host Y examines Destination MAC address, which matches its Ethernet interface MAC address, and
copies in the frame.
2. Host Y sees the Type field is 0x800, IP packet in the data field, which needs to be sent to its IP process.
3. Host Y strips off the data link, Ethernet, frame and sends it to its IP process.
Layer 3: IP Packet
4. Host Y’s IP process examines the Destination IP Address to make sure it matches its own IP Address..

If it does not, the packet will be dropped.
5. The packet’s protocol field is examined to see where to send the data portion of this IP packet: TCP,
UDP or other?
Layer 4: TCP, UDP or other?
49
Layer 2 Data Link Frame
Dest.
Dest.Add
MAC
MAC
0B-31
FF-FF
00-10
Source Add
MAC
0A-10
00-20
Layer 3 IP Packet
Type
800
Dest. IP
192.168.4.10
Source IP
192.168.1.10
IP
fields
Data
Trailer
 The summary once again!
50
CLI Configuration and
Addressing
 Implementing Basic Addressing Schemes
 Basic Router Configuration
Learning IOS: Lab 1.5.2 (Cabrillo College Version)
Networking Lab
NetLab
Packet Tracer
52
Establishing a HyperTerminal session (next week)
Router
Console port
Rollover cable
Terminal or a
PC with
terminal
emulation
software
Com1 or Com2 serial port
Take the following steps to connect a terminal to the console port on the router:
 Connect the terminal using the RJ-45 to RJ-45 rollover cable and an RJ-45 to DB-9
or RJ-45 to DB-25 adapter.
 Configure the terminal or PC terminal emulation software for 9600 baud, 8 data bits,
no parity, 1 stop bit, and no flow control.
53
Establishing a Terminal session
 Tera Term
 HyperTerminal (comes with Windows)
 Putty
=
 Important: A console connection is not the same as a network
connection!
54
When do you need to use a console connection to the router?
When there is not a network connection to the router (can’t use telnet).
What software do you need?
Tera Term, HyperTerminal, Putty, etc.
What cable and ports do you use?
PC: Serial port & Router: Console Port
Rollover or Console Cable
Terminal Connection
No network connection needed
Console Port
Serial
55
C:\> ping
C:\> telnet
Ethernet Connection
Network connection needed
NIC
When can you use a network connection to
the router? When there is a network connection to the
What
What
router (telnet).
software/command do you need? TCP/IP, Terminal prompt (DOS),
Tera Term, etc.
cable and ports do you use? PC & Router: Ethernet NIC
Ethernet straight-through cable
When should you not use a network
connection to configure the router?
When the change may
disconnect the telnet connection.
56
C:\> ping
C:\> telnet
Ethernet Connection
Network connection needed
NIC
Terminal Connection
No network connection needed
Console Port
Serial
57
NetLab
58
NetLab
Basic Router
Pod
59
Your Interfaces may differ
R1# show ip interface brief
Interface
FastEthernet0/0
FastEthernet0/1
Serial0/0
Serial0/1
IP-Address
OK?
192.168.1.1
192.168.1.2
192.168.2.1
unassigned
Method Status Protocol
YES
YES
YES
YES
manual
manual
manual
manual
up
up
up
up
up
up
up
up
FastEthernet 0 = FastEthernet 0/0
FastEthernet 1 = FastEthernet 0/1 = FastEthernet 1/0
Serial 0 = Serial 0/0 = Serial 0/0/0
Serial 1 = Serial 0/1 = Serial 0/0/1
60
Learning IOS: Lab 1.5.2 (Cabrillo College Version)
61
Command Overview (partial list from lab)
Router>
Router> enable
Router#
Router# configure terminal
Router(config)# exit
Router# config t
user mode
privilege mode
Router(config)# hostname name
Router(config)# enable secret password
Router(config)# line console 0
Router(config-line)# password password
Router(config-line)# login
Router(config)# line vty 0 4
Router(config-line)# password password
Router(config-line)# login
privilege password
console password
Router(config)# banner motd # message #
banner
Router(config)# interface type number
Router(config-if)# ip address address mask
Router(config-if)# description description
Router(config-if)# no shutdown
configure interface
telnet password
62
Other Commands
Router# copy running-config startup-config
Router#
Router#
Router#
Router#
show
show
show
show
running-config
ip route
ip interface brief
interfaces
63
Different Modes
Router# hostname R1
^
% Invalid input detected at '^' marker.
Router# configure terminal
Router(config)# hostname R1
R1(config)#
 IOS commands must be entered in the correct mode.
64
Serial Connectors
Smart
Serial
“Older”
Serial
 2500 have the “older,” larger serial interfaces
 Later Cisco routers use the smart serial interfaces which allows
more data to be forwarded across fewer cable pins.
65
Serial Connectors
DCE Cable
DTE Cable
 Router is typically a DTE device.
 The DTE cable is connected to the serial interface on the router to a
CSU/DSU device (DCE).
66
WAN Interface Configuration
R1(config)# interface Serial0/0
R1(config-if)# ip address 192.168.2.1 255.255.255.0
R1(config-if)# description Link to R2
R1(config-if)# clock rate 64000 DCE Only
R1(config-if)# no shutdown
67
Unsolicited Messages from IOS
R1(config)# interface fastethernet0/0
R1(config-if)# ip address 172.16.3.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# descri
*Mar 1 01:16:08.212: %LINK-3-UPDOWN: Interface
FastEthernet0/0, changed state to up
*Mar 1 01:16:09.214: %LINEPROTO-5-UPDOWN: Line protocol on
Interface
FastEthernet0/0, changed state to upption
R1(config-if)#
 The IOS often sends unsolicited messages
 Does not affect the command
 Can cause you to lose your place when typing.
68
Unsolicited Messages from IOS
R1(config)# line console 0
R1(config-line)# logging synchronous
R1(config-if)# descri
*Mar 1 01:28:04.242: %LINK-3-UPDOWN: Interface
FastEthernet0/0, changed state to up
*Mar 1 01:28:05.243: %LINEPROTO-5-UPDOWN: Line protocol on
Interface
FastEthernet0/0, changed state to up
R1(config-if)# description
 To keep the unsolicited output separate from your input, enter line
configuration mode for the console port and add the logging
synchronous
69
LAN Interface Configuration
R1(config)# interface FastEthernet0/0
R1(config-if)# ip address 192.168.1.1 255.255.255.0
R1(config-if)# description R1 LAN
R1(config-if)# no shutdown
Fa0/1
70
Each Interface Belongs to a Different Network
R1(config)# interface FastEthernet0/1
R1(config-if)# ip address 192.168.1.2 255.255.255.0
192.168.1.0 overlaps with FastEthernet0/0
R1(config-if)# no shutdown
192.168.1.0 overlaps with FastEthernet0/0
FastEthernet0/1: incorrect IP address assignment
192.168.1.1/24
Fa0/1
192.168.1.2/24
Same Network!
71
Each Interface Belongs to a Different Network
R1# show ip interface brief
Interface
IP-Address
FastEthernet0/0
192.168.1.1
Serial0/0
192.168.2.1
FastEthernet0/1
192.168.1.2
OK?
YES
YES
YES
Serial0/1
YES
unassigned
Method
manual
manual
manual
Status Protocol
up
up
up
up
administratively
down down
unset administratively
down down
Fa0/1
72
Verifying Interfaces
R1# show interfaces
<some interfaces not shown>
FastEthernet0/0 is up, line protocol is up (connected)
Hardware is Lance, address is 0007.eca7.1511 (bia 00e0.f7e4.e47e)
Description: R1 LAN
Internet address is 192.168.1.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec, rely 255/255, load 1/255
Encapsulation ARPA, loopback not set
ARP type: ARPA, ARP Timeout 04:00:00,
Last input 00:00:08, output 00:00:05, output hang never
Last clearing of “show interface” counters never
Queueing strategy: fifo
Output queue :0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
<output omitted>
Serial0/0 is up, line protocol is up (connected)
Hardware is HD64570
Description: Link to R2
Internet address is 192.168.2.1/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation HDLC, loopback not set, keepalive set (10 sec)
Last input never, output never, output hang never
<output omitted>
73
Verify Router Configuration
R1# show running-config
!
version 12.3
!
hostname R1
!
interface FastEthernet0/0
description R1 LAN
ip address 192.168.1.1 255.255.255.0
!
interface Serial0/0
description Link to R2
ip address 192.168.2.1 255.255.255.0
clock rate 64000
!
banner motd ^C
******************************************
WARNING!! Unauthorized Access Prohibited!!
******************************************
^C
!
line con 0
password cisco
login
line vty 0 4
password cisco
login
!
end
Note: shutdown is the
default. no shutdown does
not show in the configuration.
74
Save Configuration
R1# copy running-config startup-config
R1# show startup-config
Using 728 bytes
!
version 12.3
!
hostname R1
!
interface FastEthernet0/0
description R1 LAN
ip address 192.168.1.1 255.255.255.0
!
interface Serial0/0
description Link to R2
ip address 192.168.2.1 255.255.255.0
clock rate 64000
!
banner motd ^C
******************************************
WARNING!! Unauthorized Access Prohibited!!
******************************************
^C
line con 0
password cisco
login
line vty 0 4
password cisco
login
!
end
75
Building the Routing Table
 Introducing the Routing Table
 Directly Connected Networks

Show Routing Table
R1# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
C
C
192.168.1.0/24 is directly connected, FastEthernet0/0
192.168.2.0/24 is directly connected, Serial0/0
77
Introducing the Routing Table
R1# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
C
C
192.168.1.0/24 is directly connected, FastEthernet0/0
192.168.2.0/24 is directly connected, Serial0/0
 Routing table is a data file in RAM that is used to store route
information about:
 Directly connected networks
 Remote networks
78
Introducing the Routing Table
R1# show ip route
<output omitted>
C
C
192.168.1.0/24 is directly connected, FastEthernet0/0
192.168.2.0/24 is directly connected, Serial0/0
Exit Interfaces
 Directly connected interfaces contain the exit interface (more later)
79
Introducing the Routing Table
R1# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<output omitted>
C
C
192.168.1.0/24 is directly connected, FastEthernet0/0
192.168.2.0/24 is directly connected, Serial0/0
Directly Connected
Networks
 directly connected network is a network that is directly attached to one of
the router interfaces.
 When a router’s interface is configured with an IP address and subnet
mask, the interface becomes a host on that attached network.
 Active directly connected networks are added to the routing table.
80
Introducing the Routing Table
R1# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
<output omitted>
C
C
192.168.1.0/24 is directly connected, FastEthernet0/0
192.168.2.0/24 is directly connected, Serial0/0
Remote Network
 A remote network is a network that is not directly connected to the
router.
 A remote network is a network that can only be reached by sending
the packet to another router.
 Remote networks are added to the routing table using: (later)
 Dynamic routing protocol
 Static routes
81
Chapter 1
Introduction to Routing and
Packet Forwarding
CIS 82 Routing Protocols and Concepts
Rick Graziani
Cabrillo College
graziani@cabrillo.edu