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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
Note
 Almost everything in this chapter will be covered in more
detail in later chapters.
 This course is about understanding and to be able to
analyze/troubleshoot networks, not how to type in a
command.
 Example: show ip route
 Type in the command (easy)
 Explain what the output is displaying (more
understanding)
 Analyze why you are seeing this information but also
know if there is anything missing or if there is
something you shouldn’t be seeing.
 That is what this course is about!
2
Characteristics of a Network
Network Characteristics and Attributes
4
Topology
 Physical Topology:
 Is the arrangement of the cables, network devices, and end
systems.
 It describes how the network devices are actually interconnected
with wires and cables.
 Logical Topology:
 Is the path over which the data is transferred in a network.
 It describes how the network devices appear connected to
network users.
5
Network
Characteristics and
Attributes
 Speed:
 The measure of the data rate in bits per second (b/s) of a given
link.
 Cost:
 Indicates the general expense for purchasing of network
components, and installation and maintenance of the network.
 Security:
 Indicates how protected the network is, including the information
that is transmitted over the network.
6
Network
Characteristics and
Attributes
 Availability:
 Is a measure of the probability that the network is available for
use when it is required.
 Scalability:
 Indicates how easily the network can accommodate more users
and data transmission requirements.
 Reliability:
 Indicates the dependability of the components that make up the
network, such as the routers, switches, PCs, and servers.
 Often measured as a probability of failure or as the mean time
between failures (MTBF).
7
Routers
Why Routing?
The router is responsible for the routing of traffic between
networks.
9
What is a Router?
Leonard Kleinrock and the first IMP.
 A router is a specialized computer!
 It sends packets over the data network.
 It is responsible for interconnecting networks by selecting the best path
for a packet to travel and forwarding packets to their destination
 The first router (ARPANET):
 IMP (Interface Message Processor)
 Honeywell 516 minicomputer
 August 30, 1969
10
Router
Components
 Regardless of their function, size or complexity, all router models are
essentially computers and require:
 Operating systems (OS)
 Central processing units (CPU)
 Random-access memory (RAM)
 Read-only memory (ROM)
 Routers also have special memory that includes Flash and
nonvolatile random-access memory (NVRAM).
11
Router Memory
Memory
Volatile /
Non-Volatile
Volatile
•
•
•
•
Running IOS
Running configuration file
IP routing and ARP tables
Packet buffer
Non-Volatile
•
•
•
Bootup instructions
Basic diagnostic software
Limited IOS
Non-Volatile
•
Startup configuration file
Non-Volatile
•
•
IOS
Other system files
RAM
(Random Access
Memory)
ROM
(Read-Only
Memory)
NVRAM
(Non-Volatile RAM)
Flash
Stores
12
Router Backplane
Double-wide eHWIC slots
eHWIC 0
AUX
port
LAN
interfaces
 The backplane of a router includes:
Console
RJ45
Two 4 GB flash card slots
Console
USB Type B
USB
Ports
13
Routers vs Multilayer Switches
 Routers and multilayer switches both perform routing (connecting
networks)
 Routers may have different types of interfaces (Ethernet, serial,
ATM, etc.) while multilayer switches will only have Ethernet
interfaces.
 While routers can be used to segment LAN devices, their major use
is as WAN devices.
 Each devices does have its own advantages.
 Routers are:
 The backbone devices of large intranets and of the Internet
 They operate at Layer 3 (network layer) of the OSI model
 They make decisions based on network addresses (IPv4, IPv6).
14
Routers in LANs and WANs
 Routers can connect multiple networks.
 Routers have multiple interfaces, each on a different IP
network.
15
Best Path
Decisions
 The primary responsibility of a router is to direct packets by:
 Determining the best path to send packets
 Forwarding packets toward their destination
16
Best Path Decisions
 Routers use routing tables to determine the best path to send packets.
 Routers encapsulate the packet and forward it to the interface indicated
in routing table.
17
Router
Functions
 Routing tables can be created:
 Manually with static routes
 Dynamically with routing protocols
 Routing protocols exchanges network topology (path) information
with other routers.
18
Best Path Decisions
 The router uses its routing table to determine the best path to
forward the packet.
 When the router receives a packet, it examines its destination IP
address and searches for the best network address match in the
routing table.
 The routing table entries also includes the interface to be used to
forward the packet.
 Once a match is found, the router encapsulates the IP packet
into the data link frame of the outgoing or exit interface.
 The packet is then forwarded toward its destination.
 Routers support three packet-forwarding mechanisms:
 Process switching
 Fast Switching
 Cisco Express Forwarding (CEF)
19
Analogy: Process switching solves a
problem by doing math long hand, even if it
is the identical problem.
Process
Switching
Control Plane
IP Routing Table
CPU
Ingress Interface
1st Packet
Data Plane
Egress Interface
2nd Packet
3rd Packet
4th Packet
5th Packet
 Earliest switching method. (Applies to both routers and multilayer
switches.)
 This is an older packet forwarding mechanism.
 When a packet arrives on an interface, it is forwarded to the
control plane where the CPU examines the routing table,
determines the exit interface and forwards the packet.
 It does this for every packet, even if the destination is the same
for a stream of packets.
20
Fast Switching
Analogy: Fast switching solves a problem by
doing math long hand one time and remembering
the answer for subsequent identical problems.
Control Plane
IP Routing Table
CPU
Ingress Interface
Data Plane
1st Packet
2nd Packet
3rd Packet
4th Packet
5th Packet
Egress Interface
Fast
Forward
Cache
 As routers had to process more packets, it was determined process
switching was not fast enough.
 Next evolution in packet switching was Fast Switching. (Applies to both
routers and multilayer switches.)
 The first packet is process-switched (CPU + routing table) but it also
uses a fast-switching cache to store next-hop information of the flow.
 The next packets in the flow are forwarded using the cache and
21
without CPU intervention.
Analogy: CEF solves every possible
problem ahead of time in a spreadsheet.
CEF Switching
Control Plane
CPU
Ingress Interface
1st Packet
2nd Packet
3rd Packet
4th Packet
5th Packet
Data Plane
Egress Interface
FIB and
Adjacency
Table
 Preferred and default Cisco IOS packet-forwarding mechanism for
routers and multilayer switches.
 CEF copies the routing table to the Forwarding Information Base
(FIB)
 CEF creates an adjacency table which contains all the layer 2
information a router would have to consider when forwarding a
packet such as Ethernet destination MAC address.
 The adjacency table is created from the ARP table.
 CEF is discussed in more detail in CIS 187 CCNP SWITCH.
22
Connect Devices
Home Office Devices Connect …
 Laptops and tablets connect
wirelessly to a home router.
 A network printer connects using
an Ethernet cable to the switch port
on the home router.
 The home router connects to the
service provider cable modem
using an Ethernet cable.
 The cable modem connects to the
Internet service provider (ISP)
network.
24
Branch Site Devices Connect …
• Corporate resources (i.e., file
servers and printers) connect to
Layer 2 switches.
• PCs and VoIP phones connect to
Layer 2 Ethernet switches.
• Laptops and smartphones connect
wirelessly to WAPs.
• WAPs connect to switches.
• Layer 2 switches connect to the
edge router.
• The edge router connects to a WAN
service provider (SP) and an ISP for
backup purposes.
25
Central Site Devices Connect …
• PCs and VoIP phones connect to
Layer 2 Ethernet switches.
• Layer 2 switches connect to Layer 3
switches using Ethernet fiber-optic
cables.
• Layer 3 switches connect to the
edge router.
• The corporate website server is
connected to the edge router
interface.
• The edge router connects to a WAN
SP and an ISP for backup purposes.
26
Default
Gateways
 To enable network access, devices must be configured with IP
address information to identify the appropriate:
 IP address - Identifies a unique host on a local network.
 Subnet mask - Identifies with which network subnet the host
can communicate.
 Default gateway - Identifies the router to send a packet to when
the destination is not on the same local network subnet.
27
Documenting
a Network
 Network documentation should identify:
 Device names
 Interfaces used in the design
 IP addresses and subnet masks
 Default gateway addresses
 Useful documents include:
 Network topology diagram
 Addressing Table
28
Documenting a Network
192.168.1.0/24
192.168.2.0/24
.1
.10
.1
192.168.3.0/24
.2
.1
.10
29
Hosts Addressing
 A host can be assigned IP address
information either:
 Statically - The host is manually
assigned the correct IP address,
subnet mask, and default gateway.
The DNS server IP address can also
be configured.
 Dynamically - IP address
information is provided by a server
using the Dynamic Host
Configuration Protocol (DHCP). The
DHCP server provides a valid IP
address, subnet mask, and default
gateway for end devices. Other
information may be provided by the
server.
30
Device LEDs
 Most network interfaces have one or two LED link indicators next to
the interface.
 Generally:
 Green LED means a good connection
 Blinking green LED indicates network activity.
 No light then there may be a problem with either the network
cable or the network itself.
 The switch port where the connection terminates would also have an
LED indicator lit.
 If one or both ends are not lit, try a different network cable.
31
Cisco 1941 LEDs
32
Console Connection
SSH
Console Connection
 In a production environment, infrastructure devices are commonly
accessed remotely using Secure Shell (SSH) or HyperText Transfer
Protocol Secure (HTTPS).
 Console access is really only required when initially configuring a
device, if remote access fails, or if the change may affect the remote
access.
 Console access requires:
 Console cable – RJ-45-to-DB-9 console cable
 Terminal emulation software – Tera Term, PuTTY,
HyperTerminal
33
USB Serial Console Connection
 The Cisco ISR G2 supports a USB serial
console connection.
 To establish connectivity, a USB Type-A
to USB Type-B (mini-B USB) is required,
as well as an operating system device
driver.
 This device driver is available from
http://www.cisco.com.
 Although these routers have two console
ports, only one console port can be active at a
time.
 When a cable is plugged into the USB
console port, the RJ-45 port becomes
inactive.
 When the USB cable is removed from the
USB port, the RJ-45 port becomes active.
34
Console Connection Requirements
Port on
Computer
Serial port
Cable required
Port on ISR
• RJ45-to-DB9 console cable
RJ45 Console port
USB
Type-A port
Terminal
emulation
• USB-to-RS232 compatible serial
port adapter
• Adapter may require a software
driver
• RJ45-to-DB9 console cable
• USB Type-A to USB Type-B (mini-B
USB)
• An device driver is required and
available from cisco.com.
USB Type-B
(mini-B USB)
Tera Term
PuTTY
35
Console Connection Requirements
Port on
Computer
Cable required
Port on ISR
Terminal
emulation
Serial port
RJ45 Console port
Tera Term
USB
Type-A port
• USB Type-A to USB Type-B (mini-B
USB)
• An device driver is required and
available from cisco.com.
USB Type-B
(mini-B USB)
PuTTY
36
Configuring Routers
Name the Device
.2
.2
Router# configure terminal
Enter configuration commands, one per line.
Router(config)# hostname R1
R1(config)#
End with CNTL/Z.
38
Secure Management Access
.2
.2
R1(config)# enable secret class
R1(config)# username admin secret class
R1(config)# line console 0
R1(config-line)# password cisco
R1(config-line)# login
R1(config-line)# exit
R1(config)# ip domain-name cisco.com
R1(config)# crypto key generate rsa 1024
R1(config)# line vty 0 4
R1(config-line)# transport input ssh
R1(config-line)# login local
R1(config-line)# exit
R1(config)# service password-encryption
R1(config)#
39
Configure a Banner
.2
.2
R1(config)# banner motd $ Authorized Access Only! $
R1(config)#
40
Save the Configuration
.2
.2
R1# copy running-config startup-config
Destination filename [startup-config]?
Building configuration...
[OK]
R1#
41
Configure Basic Settings on R2
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)# enable secret class
R2(config)# username admin secret class
R2(config)# line console 0
R2(config-line)# password cisco
R2(config-line)# login
R2(config-line)# exit
R2(config)# ip domain-name cisco.com
R2(config)# crypto key generate rsa 1024
R2(config)# line vty 0 4
R2(config-line)# transport input ssh
R2(config-line)# login local
R2(config-line)# exit
R2(config)#
R2(config)# service password-encryption
R2(config)#
R2(config)# banner motd $ Authorized Access Only! $
R2(config)# end
R2# copy running-config startup-config
Destination filename [startup-config]?
Building configuration...
[OK]
R2#
42
Configure the Gi0/0 Interface
.2
.2
R1(config)# interface gigabitethernet 0/0
R1(config-if)# description Link to LAN 1
R1(config-if)# ip address 192.168.10.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)#
*Jan 30 22:04:47.551: %LINK-3-UPDOWN: Interface
GigabitEthernet0/0, changed state to down
R1(config)#
*Jan 30 22:04:50.899: %LINK-3-UPDOWN: Interface
GigabitEthernet0/0, changed state to up
*Jan 30 22:04:51.899: %LINEPROTO-5-UPDOWN: Line protocol on
Interface GigabitEthernet0/0, changed state to up
R1(config)#
43
Configure the Gi0/1 Interface
.2
.2
R1(config)# interface gigabitethernet 0/1
R1(config-if)# description Link to LAN 2
R1(config-if)# ip address 192.168.11.1 255.255.255.0
R1(config-if)# no shutdown
R1(config-if)# exit
*Jan 30 22:06:02.543: %LINK-3-UPDOWN: Interface
GigabitEthernet0/1, changed state to down
R1(config)#
*Jan 30 22:06:05.899: %LINK-3-UPDOWN: Interface
GigabitEthernet0/1, changed state to up
*Jan 30 22:06:06.899: %LINEPROTO-5-UPDOWN: Line protocol on
Interface GigabitEthernet0/1, changed state to up
R1(config)#
44
Configure the S0/0/0 Interface
.2
.2
R1(config)# interface serial 0/0/0
R1(config-if)# description Link to R2
R1(config-if)# ip address 209.165.200.225 255.255.255.252
R1(config-if)# clockrate 128000
R1(config-if)# no shutdown
R1(config-if)# exit
*Jan 30 23:01:17.323: %LINK-3-UPDOWN: Interface
Serial0/0/0, changed state to down
R1(config)#
45
Configure the R2 Interfaces
R2(config)#interface gigabitethernet 0/0
R2(config-if)#description Link to LAN 3
R2(config-if)#ip address 10.1.1.1 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#exit
*Jan 30 23:08:34.139: Output omitted
R2(config)#
R2(config)#interface gigabitethernet 0/1
R2(config-if)#description Link to LAN 4
R2(config-if)#ip address 10.1.2.1 255.255.255.0
R2(config-if)#no shutdown
R2(config-if)#exit
*Jan 30 23:09:56.915: Output omitted
R2(config)#
R2(config)#interface serial 0/0/0
R2(config-if)#description Link to R1
R2(config-if)#ip address 209.165.200.226 255.255.255.252
R2(config-if)#no shutdown
R2(config-if)#exit
*Jan 30 23:09:18.451: %LINK-3-UPDOWN: Interface Serial0/0/0, changed
state to up
*Jan 30 23:09:19.451: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Serial0/0/0, changed state to up
R2(config)#
R1’s Serial 0/0/0 interface will also now be in the up state
46
Statically Assign IPv6 Address to Host
2001:0DB8:ACAD:1::/64
PC1
PC2
:10
:10
2001:0DB8:ACAD:3::/64
G0/0
:1
:1
G0/1
R1
:1
S0/0/0
2001:0DB8:ACAD:2::/64
47
Configuring IPv6 Address on Gi0/0
2001:0DB8:ACAD:1::/64
PC1
PC2
:10
:10
2001:0DB8:ACAD:3::/64
G0/0
:1
:1
G0/1
R1
:1
S0/0/0
2001:0DB8:ACAD:2::/64
R1(config)# interface gigabitethernet 0/0
R1(config-if)# description Link to LAN 1
R1(config-if)# ipv6 address 2001:db8:acad:1::1/64
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)#
*Feb 3 21:38:37.279: %LINK-3-UPDOWN: Interface
GigabitEthernet0/0, changed state to down
*Feb 3 21:38:40.967: %LINK-3-UPDOWN: Interface
GigabitEthernet0/0, changed state to up
*Feb 3 21:38:41.967: %LINEPROTO-5-UPDOWN: Line protocol on
Interface GigabitEthernet0/0, changed state to up
R1(config)#
48
Configuring IPv6 Address on Gi0/1
2001:0DB8:ACAD:1::/64
PC1
PC2
:10
:10
2001:0DB8:ACAD:3::/64
G0/0
:1
:1
G0/1
R1
:1
S0/0/0
2001:0DB8:ACAD:2::/64
R1(config)# interface gigabitethernet 0/1
R1(config-if)# description Link to LAN 2
R1(config-if)# ipv6 address 2001:db8:acad:2::1/64
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)#
*Feb 3 21:39:21.867: %LINK-3-UPDOWN: Interface
GigabitEthernet0/1, changed state to down
*Feb 3 21:39:24.967: %LINK-3-UPDOWN: Interface
GigabitEthernet0/1, changed state to up
*Feb 3 21:39:25.967: %LINEPROTO-5-UPDOWN: Line protocol on
Interface GigabitEthernet0/1, changed state to up
R1(config)#
49
Configuring IPv6 Address on S0/0/0
2001:0DB8:ACAD:1::/64
PC1
PC2
:10
:10
2001:0DB8:ACAD:3::/64
G0/0
:1
:1
G0/1
R1
:1
S0/0/0
2001:0DB8:ACAD:2::/64
R1(config)# interface serial 0/0/0
R1(config-if)# description Link to R2
R1(config-if)# ipv6 address 2001:db8:acad:3::1/64
R1(config-if)# clock rate 128000
R1(config-if)# no shutdown
R1(config-if)#
*Feb 3 21:39:43.307: %LINK-3-UPDOWN: Interface Serial0/0/0,
changed state to down
R1(config-if)#
50
Configuring the R2 Interfaces
2001:0DB8:ACAD:0003::/64
:2
S0/0/0
2001:0DB8:ACAD:0004::/64
:10
G0/0
:1
R2
G0/1
:1
.:10
2001:0DB8:ACAD:0005::/64
R2(config)#interface gigabitethernet 0/0
R2(config-if)#description Link to LAN 3
R2(config-if)#ipv6 address 2001:db8:acad:4::1/64
R2(config-if)#no shutdown
R2(config-if)#exit
R2(config)#interface gigabitethernet 0/1
R2(config-if)#description Link to LAN 4
R2(config-if)#ipv6 address 2001:db8:acad:5::1/64
R2(config-if)#no shutdown
R2(config-if)#exit
R2(config)#interface serial 0/0/0
R2(config-if)#description Link to R1
R2(config-if)#ipv6 address 2001:db8:acad:3::2/64
R2(config-if)#no shutdown
51
Verify Summary Interface Status
.2
.2
R1# show ip interface brief
Interface
IP-Address
OK? Method Status
Protocol
Embedded-Service-Engine0/0 unassigned
YES unset administratively down
GigabitEthernet0/0
192.168.10.1
YES manual up
GigabitEthernet0/1
192.168.11.1
YES manual up
Serial0/0/0
209.165.200.225 YES manual up
Serial0/0/1
unassigned
YES unset administratively down down
down
up
up
up
R1#
52
Verify Routing Table
.2
.2
R1# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
<output omitted.
Gateway of last resort is not set
C
L
C
L
C
L
R1#
192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks
192.168.10.0/24 is directly connected, GigabitEthernet0/0 Network Address
192.168.10.1/32 is directly connected, GigabitEthernet0/0 Interface Address
192.168.11.0/24 is variably subnetted, 2 subnets, 2 masks
192.168.11.0/24 is directly connected, GigabitEthernet0/1 Network Address
192.168.11.1/32 is directly connected, GigabitEthernet0/1 Interface Address
209.165.200.0/24 is variably subnetted, 2 subnets, 2 masks
209.165.200.224/30 is directly connected, Serial0/0/0
Network Address
209.165.200.225/32 is directly connected, Serial0/0/0
Interface Address
53
Verify Interface Configuration
.2
.2
R1# show running-config interface gigabitEthernet 0/0
Building configuration...
Current configuration : 128 bytes
!
interface GigabitEthernet0/0
description Link to LAN 1
ip address 192.168.10.1 255.255.255.0
duplex auto
speed auto
end
R1#
54
Verifying the R1 Gi0/0 Interface
R1#show interfaces gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is fc99.4775.c3e0 (bia
fc99.4775.c3e0)
Description: Link to LAN 1
Internet address is 192.168.10.1/24
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full Duplex, 100Mbps, media type is RJ45
output flow-control is unsupported, input flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:05:21, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
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
329 packets input, 70930 bytes, 0 no buffer
Received 298 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 0 multicast, 0 pause input
437 packets output, 47524 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
30 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
R1#
55
Verify the R1 Gi0/1 Interface
R1# show interfaces gigabitEthernet 0/1
GigabitEthernet0/1 is up, line protocol is up
Hardware is CN Gigabit Ethernet, address is fc99.4775.c3e1 (bia
fc99.4775.c3e1)
Description: Link to LAN 2
Internet address is 192.168.11.1/24
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Full Duplex, 100Mbps, media type is RJ45
output flow-control is unsupported, input flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:11, output 00:00:02, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
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
614 packets input, 125730 bytes, 0 no buffer
Received 585 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 306 multicast, 0 pause input
717 packets output, 77198 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
228 unknown protocol drops
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 pause output
0 output buffer failures, 0 output buffers swapped out
R1#
56
Verify the R1 Serial Interface
R1# show interfaces serial 0/0/0
Serial0/0/0 is up, line protocol is up
Hardware is WIC MBRD Serial
Description: Link to R2
Internet address is 209.165.200.225/30
MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation HDLC, loopback not set
Keepalive set (10 sec)
Last input 00:00:03, output 00:00:02, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
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
714 packets input, 52752 bytes, 0 no buffer
Received 714 broadcasts (0 IP multicasts)
0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
714 packets output, 53070 bytes, 0 underruns
0 output errors, 0 collisions, 3 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out
1 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
R1#
57
Verify the R1 Interface Status
2001:0DB8:ACAD:1::/64
PC1
PC2
:10
:10
2001:0DB8:ACAD:3::/64
G0/0
:1
:1
G0/1
R1
:1
S0/0/0
2001:0DB8:ACAD:2::/64
R1# show ipv6 interface brief
GigabitEthernet0/0
[up/up]
FE80::FE99:47FF:FE75:C3E0
Link Local Address (created automatically)
2001:DB8:ACAD:1::1
Global Unicast Address (configured)
GigabitEthernet0/1
[up/up]
FE80::FE99:47FF:FE75:C3E1
Link Local Address (created automatically)
2001:DB8:ACAD:2::1
Global Unicast Address (configured)
Serial0/0/0
[up/up]
FE80::FE99:47FF:FE75:C3E0
Link Local Address (created automatically)
2001:DB8:ACAD:3::1
Global Unicast Address (configured)
Serial0/0/1
[administratively down/down]
unassigned
R1#
58
Verify the R1 Routing Table
2001:0DB8:ACAD:1::/64
PC1
PC2
:10
:10
2001:0DB8:ACAD:3::/64
G0/0
:1
:1
G0/1
R1
:1
S0/0/0
2001:0DB8:ACAD:2::/64
R1# show ipv6 interface gigabitEthernet 0/0
GigabitEthernet0/0 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::32F7:DFF:FEA3:DA0
No Virtual link-local address(es):
Global unicast address(es):
2001:DB8:ACAD:1::1, subnet is 2001:DB8:ACAD:1::/64
Joined group address(es):
FF02::1
FF02::1:FF00:1
FF02::1:FFA3:DA0
MTU is 1500 bytes
ICMP error messages limited to one every 100 milliseconds
ICMP redirects are enabled
ICMP unreachables are sent
ND DAD is enabled, number of DAD attempts: 1
ND reachable time is 30000 milliseconds (using 30000)
ND NS retransmit interval is 1000 milliseconds
R1#
59
Verify Connectivity
2001:0DB8:ACAD:1::/64
PC1
PC2
:10
2001:0DB8:ACAD:3::/64
G0/0
:1
:1
G0/1
:10
R1
:1
S0/0/0
2001:0DB8:ACAD:2::/64
R1# show ipv6 route
IPv6 Routing Table - default - 7 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user
Static
<output omitted>
C
L
C
L
C
L
L
R1#
2001:DB8:ACAD:1::/64 [0/0]
via GigabitEthernet0/0, directly connected
2001:DB8:ACAD:1::1/128 [0/0]
via GigabitEthernet0/0, receive
2001:DB8:ACAD:2::/64 [0/0]
via GigabitEthernet0/1, directly connected
2001:DB8:ACAD:2::1/128 [0/0]
via GigabitEthernet0/1, receive
2001:DB8:ACAD:3::/64 [0/0]
via Serial0/0/0, directly connected
2001:DB8:ACAD:3::1/128 [0/0]
via Serial0/0/0, receive
FF00::/8 [0/0]
via Null0, receive
60
Verify the R1 Interface Status
2001:0DB8:ACAD:1::/64
PC1
PC2
:10
:10
2001:0DB8:ACAD:3::/64
G0/0
:1
:1
G0/1
R1
:1
S0/0/0
2001:0DB8:ACAD:2::/64
R1# ping 2001:db8:acad:1::10
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8:ACAD:1::10,
timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5)
R1#
61
Tweaking Show Command Output
R1#show ip interface brief
Interface
Embedded-Service-Engine0/0
GigabitEthernet0/0
GigabitEthernet0/1
Serial0/0/0
Serial0/0/1
R1#
R1#show ip interface brief
GigabitEthernet0/0
GigabitEthernet0/1
Serial0/0/0
R1#
IP-Address
unassigned
192.168.10.1
192.168.11.1
209.165.200.225
unassigned
OK?
YES
YES
YES
YES
YES
Method
unset
manual
manual
manual
unset
Status
Protocol
administratively down down
up
up
up
up
up
up
administratively down down
| include up
192.168.10.1
YES manual up
192.168.11.1
YES manual up
209.165.200.225 YES manual up
up
up
up
63
Tweaking Show Command Output
R1#show ip route | begin Gateway
Gateway of last resort is not set
C
L
C
L
C
L
R1#
192.168.10.0/24 is variably subnetted, 2 subnets, 2 masks
192.168.10.0/24 is directly connected, GigabitEthernet0/0
192.168.10.1/32 is directly connected, GigabitEthernet0/0
192.168.11.0/24 is variably subnetted, 2 subnets, 2 masks
192.168.11.0/24 is directly connected, GigabitEthernet0/1
192.168.11.1/32 is directly connected, GigabitEthernet0/1
209.165.200.0/24 is variably subnetted, 2 subnets, 2 masks
209.165.200.224/30 is directly connected, Serial0/0/0
209.165.200.225/32 is directly connected, Serial0/0/0
64
Tweaking Show Command Output
R1#show running-config | section line con
line con 0
password 7 110A1016141D
login
R1#
R1#show ip interface brief | include down
Embedded-Service-Engine0/0 unassigned
YES unset
Serial0/0/1
unassigned
YES unset
R1#
R1#show ip interface brief | exclude up
Interface
IP-Address
OK? Method
Protocol
Embedded-Service-Engine0/0 unassigned
YES unset
Serial0/0/1
unassigned
YES unset
R1#
R1#show running-config | begin line
line con 0
password 7 110A1016141D
login
line aux 0
line 2
no activation-character
no exec
transport preferred none
transport input all
transport output pad telnet rlogin lapb-ta mop udptn
stopbits 1
line vty 0 4
password 7 030752180500
login
transport input all
!
administratively down down
administratively down down
Status
administratively down down
administratively down down
v120 ssh
65
Command History Feature
R1#terminal history size 200
R1#
R1#show history
show ip interface brief
show interface g0/0
show ip interface g0/1
show ip route
show ip route 209.165.200.224
show running-config interface s0/0/0
terminal history size 200
show history
R1#
The command history feature temporarily stores a list of executed commands:
 To recall commands press Ctrl+P or the UP Arrow.
 To return to more recent commands press Ctrl+N or the Down Arrow.
 By default, command history is enabled and the system captures the last 10
commands in the buffer.
 Use the show history privileged EXEC command to display the buffer contents.
 Use the terminal history size user EXEC command to increase or decrease size
66
of the buffer.
Routers Operate at Layers 1, 2, and 3
(Decisions made at Layer 3)
67
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…
68
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…
69
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
70
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
71
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
72
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
73
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
74
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!
75
Routing Decisions
76
Alex Zinin’s Routing Table Principles
I know about my remote
networks but it is not my
responsibility if R2 and R3
know about their remote
networks.
 Principle 1: Every router makes its decision alone, based on the
information it has in its own routing table.
 R1 makes forwarding decisions based solely on the information in the
routing table.
 R1 does not consult the routing tables in any other routers.
 Making each router aware of remote networks is the responsibility of the
network administrator.
77
Alex Zinin’s Routing Table Principles
Just because I know how to
get to R3’s LAN,
192.168.2.0/24 and I send
that packet to R2, doesn’t
mean R2 knows how to get
there.
???
 Principle 2: The fact that one router has certain information in its
routing table does not mean that other routers have the same
information.
78
Alex Zinin’s Routing Table Principles
And if the packet for R3’s
LAN reaches 192.168.2.0/24,
I don’t know if R3 has a
route back to 172.16.3.0/24
for any return traffic.
???
 Principle 3: Routing information about a path from one network
to another does not provide routing information about the
reverse, or return, path.
79
Best Path
Which path is
my “best path”?
RIP’s metric is hop count
OSPF’s metric is
bandwidth
?
EIGRP is bandwidth +
delay
 Router’s determine best-path to a network:
 Depends on the routing protocol
 A protocol used to between routers to determine “best path”
 Routing protocols use their own rules and metrics.
 A metric:
 Quantitative value used to measure the distance to a given route.
 Best path:
 Path with the lowest metric.
80
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.
All routing protocols (RIP, EIGRP, OSPF) support equal
cost load balancing; EIGRP also supports unequal cost
load balancing.
81
Path Determination of the route
Administrative Distance
If multiple paths to a destination are configured on a router, the path
installed in the routing table is the one with the lowest Administrative
Distance (AD):
• A static route with an AD of 1 is more reliable than an EIGRPdiscovered route with an AD of 90.
• A directly connected route with an AD of 0 is more reliable than a
static route with an AD of 1.
82
The Routing Table
The Routing Table
A routing table is a file stored in RAM that contains information about:
 Directly connected routes
 Remote routes
 Network or next hop associations
83
The show ip route and show ipv6 route commands are used to
display the contents of the routing table:
Local route interfaces - Added to the routing table when an
interface is configured. (displayed in IOS 15 or newer)
Directly connected interfaces - Added to the routing table when an
interface is configured and active.
Static routes - Added when a route is manually configured and the
exit interface is active.
Dynamic routing protocol - Added when EIGRP or OSPF are
implemented and networks are identified.
84
Interpreting the entries in the routing table.
85
Directly Connected Interfaces
A newly deployed router, without any configured interfaces, has an
empty routing table.
An active, configured, directly connected interface creates two routing
table entries:
 Local (L)
 Directly Connected (C)
86
Directly Connected Example
A routing table with
the directly
connected interfaces
of R1 configured
and activated.
87
Directly Connected IPv6 Example
The show ipv6 route command shows the ipv6 networks and routes
installed in the routing table.
88
Statically Learned Routes
Static Routes
Static routes and default static routes can be implemented after
directly connected interfaces are added to the routing table:
 Static routes are manually configured
 Covered in Chapter 6
89
Static Routes Example
90
Default Static Routes Example
91
Dynamic Routing (Chapters 7 and later)
Dynamic routing is used by routers to share information about the
reachability and status of remote networks.
It performs network discovery and maintains routing tables.
92
IPv4 and IPv6 Routing Protocols
Cisco ISR routers can support a variety of dynamic IPv4 routing
protocols including:
EIGRP – Enhanced Interior Gateway Routing Protocol
OSPF – Open Shortest Path First
IS-IS – Intermediate System-to-Intermediate System
RIP – Routing Information Protocol
Cisco ISR routers can support a variety of dynamic IPv6 routing
protocols including:
RIPng - RIP next generation
OSPFv3
EIGRP for IPv6
MP-BGP4 - Multicast Protocol-Border Gateway Protocol
93