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

NoteAlmost 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?

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

Leonard Kleinrock and the first IMP.

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-VolatileStores

RAM

(Random Access Memory)

Volatile

• Running IOS• Running configuration file• IP routing and ARP tables• Packet buffer

ROM(Read-Only

Memory)Non-Volatile

• Bootup instructions• Basic diagnostic software• Limited IOS

NVRAM(Non-Volatile RAM)

Non-Volatile • Startup configuration file

Flash Non-Volatile• IOS• Other system files

12

Router Backplane

The backplane of a router includes:

Two 4 GB flash card slots

Double-wide eHWIC slots eHWIC 0 AUX port

LANinterfaces

USB Ports

Console USB Type B

Console RJ45

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

Process Switching

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.

Control Plane

CPU

Data Plane1st Packet

2nd Packet

3rd Packet4th Packet5th Packet

Ingress Interface Egress Interface

Analogy: Process switching solves a problem by doing math long hand, even if it is the identical problem.

IP Routing Table

20

Fast Switching

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

without CPU intervention.

Control Plane

CPU

Data Plane1st Packet

2nd Packet

3rd Packet4th Packet5th Packet

Ingress Interface Egress Interface

Fast Forward Cache

Analogy: Fast switching solves a problem by doing math long hand one time and remembering the answer for subsequent identical problems.

IP Routing Table

21

CEF Switching

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.

Control Plane

CPU

Data Plane1st Packet

2nd Packet

3rd Packet4th Packet5th Packet

Ingress Interface Egress Interface

FIB and Adjacency

Table

Analogy: CEF solves every possible problem ahead of time in a spreadsheet.

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

.1

192.168.2.0/24 192.168.3.0/24

.1.2 .1

.10 .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

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

SSH Console Connection

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

Cable required Port on ISRTerminal emulation

Serial port • RJ45-to-DB9 console cable

RJ45 Console portTera Term

PuTTY

USB Type-A port

• 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)

35

Console Connection Requirements

Port on Computer

Cable required Port on ISRTerminal emulation

Serial port

RJ45 Console portTera Term

PuTTY

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)

36

Configuring Routers

Name the Device

Router# configure terminalEnter configuration commands, one per line. End with CNTL/Z.Router(config)# hostname R1R1(config)#

.2

.2

38

Secure Management Access

R1(config)# enable secret classR1(config)# username admin secret classR1(config)# line console 0R1(config-line)# password ciscoR1(config-line)# loginR1(config-line)# exitR1(config)# ip domain-name cisco.comR1(config)# crypto key generate rsa 1024R1(config)# line vty 0 4R1(config-line)# transport input sshR1(config-line)# login localR1(config-line)# exitR1(config)# service password-encryptionR1(config)#

.2

.2

39

Configure a Banner

R1(config)# banner motd $ Authorized Access Only! $R1(config)#

.2

.2

40

Save the Configuration

R1# copy running-config startup-configDestination filename [startup-config]? Building configuration...[OK]R1#

.2

.2

41

Configure Basic Settings on R2Router# configure terminalEnter configuration commands, one per line. End with CNTL/Z.R2(config)# enable secret classR2(config)# username admin secret classR2(config)# line console 0R2(config-line)# password ciscoR2(config-line)# loginR2(config-line)# exitR2(config)# ip domain-name cisco.comR2(config)# crypto key generate rsa 1024R2(config)# line vty 0 4R2(config-line)# transport input sshR2(config-line)# login localR2(config-line)# exitR2(config)# R2(config)# service password-encryptionR2(config)#R2(config)# banner motd $ Authorized Access Only! $R2(config)# endR2# copy running-config startup-configDestination filename [startup-config]? Building configuration...[OK]R2#

42

Configure the Gi0/0 Interface

R1(config)# interface gigabitethernet 0/0R1(config-if)# description Link to LAN 1 R1(config-if)# ip address 192.168.10.1 255.255.255.0R1(config-if)# no shutdownR1(config-if)# exitR1(config)#*Jan 30 22:04:47.551: %LINK-3-UPDOWN: Interface GigabitEthernet0/0, changed state to downR1(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)#

.2

.2

43

Configure the Gi0/1 Interface

R1(config)# interface gigabitethernet 0/1 R1(config-if)# description Link to LAN 2 R1(config-if)# ip address 192.168.11.1 255.255.255.0R1(config-if)# no shutdownR1(config-if)# exit*Jan 30 22:06:02.543: %LINK-3-UPDOWN: Interface GigabitEthernet0/1, changed state to downR1(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 upR1(config)#

.2

.2

44

Configure the S0/0/0 Interface

R1(config)# interface serial 0/0/0 R1(config-if)# description Link to R2R1(config-if)# ip address 209.165.200.225 255.255.255.252R1(config-if)# clockrate 128000R1(config-if)# no shutdownR1(config-if)# exit*Jan 30 23:01:17.323: %LINK-3-UPDOWN: Interface Serial0/0/0, changed state to downR1(config)#

.2

.2

45

Configure the R2 InterfacesR2(config)#interface gigabitethernet 0/0 R2(config-if)#description Link to LAN 3 R2(config-if)#ip address 10.1.1.1 255.255.255.0R2(config-if)#no shutdownR2(config-if)#exit*Jan 30 23:08:34.139: Output omittedR2(config)#R2(config)#interface gigabitethernet 0/1 R2(config-if)#description Link to LAN 4 R2(config-if)#ip address 10.1.2.1 255.255.255.0R2(config-if)#no shutdownR2(config-if)#exit*Jan 30 23:09:56.915: Output omittedR2(config)#R2(config)#interface serial 0/0/0 R2(config-if)#description Link to R1 R2(config-if)#ip address 209.165.200.226 255.255.255.252R2(config-if)#no shutdownR2(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 upR2(config)# R1’s Serial 0/0/0 interface will also now be in the up state

46

Statically Assign IPv6 Address to Host2001:0DB8:ACAD:1::/64

:10

:10 :1G0/1

:1S0/0/0

G0/0:1

R1

PC1

PC2

2001:0DB8:ACAD:2::/64

2001:0DB8:ACAD:3::/64

47

Configuring IPv6 Address on Gi0/0

R1(config)# interface gigabitethernet 0/0R1(config-if)# description Link to LAN 1R1(config-if)# ipv6 address 2001:db8:acad:1::1/64R1(config-if)# no shutdownR1(config-if)# exitR1(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 upR1(config)#

2001:0DB8:ACAD:1::/64:10

:10 :1G0/1

:1S0/0/0

G0/0:1

R1

PC1

PC2

2001:0DB8:ACAD:2::/64

2001:0DB8:ACAD:3::/64

48

Configuring IPv6 Address on Gi0/1

R1(config)# interface gigabitethernet 0/1 R1(config-if)# description Link to LAN 2R1(config-if)# ipv6 address 2001:db8:acad:2::1/64R1(config-if)# no shutdownR1(config-if)# exitR1(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 upR1(config)#

2001:0DB8:ACAD:1::/64:10

:10 :1G0/1

:1S0/0/0

G0/0:1

R1

PC1

PC2

2001:0DB8:ACAD:2::/64

2001:0DB8:ACAD:3::/64

49

Configuring IPv6 Address on S0/0/0

R1(config)# interface serial 0/0/0 R1(config-if)# description Link to R2R1(config-if)# ipv6 address 2001:db8:acad:3::1/64R1(config-if)# clock rate 128000R1(config-if)# no shutdownR1(config-if)#*Feb 3 21:39:43.307: %LINK-3-UPDOWN: Interface Serial0/0/0, changed state to downR1(config-if)#

2001:0DB8:ACAD:1::/64:10

:10 :1G0/1

:1S0/0/0

G0/0:1

R1

PC1

PC2

2001:0DB8:ACAD:2::/64

2001:0DB8:ACAD:3::/64

50

Configuring the R2 Interfaces

R2:2

S0/0/0

:10

.:10

2001:0DB8:ACAD:0004::/64

2001:0DB8:ACAD:0005::/64

2001:0DB8:ACAD:0003::/64

R2(config)#interface gigabitethernet 0/0R2(config-if)#description Link to LAN 3R2(config-if)#ipv6 address 2001:db8:acad:4::1/64R2(config-if)#no shutdownR2(config-if)#exitR2(config)#interface gigabitethernet 0/1 R2(config-if)#description Link to LAN 4R2(config-if)#ipv6 address 2001:db8:acad:5::1/64R2(config-if)#no shutdownR2(config-if)#exitR2(config)#interface serial 0/0/0 R2(config-if)#description Link to R1R2(config-if)#ipv6 address 2001:db8:acad:3::2/64R2(config-if)#no shutdown

G0/0:1

G0/1:1

51

Verify Summary Interface Status

R1# show ip interface brief Interface IP-Address OK? Method Status ProtocolEmbedded-Service-Engine0/0 unassigned YES unset administratively down down GigabitEthernet0/0 192.168.10.1 YES manual up up GigabitEthernet0/1 192.168.11.1 YES manual up up Serial0/0/0 209.165.200.225 YES manual up up Serial0/0/1 unassigned YES unset administratively down down R1#

.2

.2

52

Verify Routing Table

R1# show ip routeCodes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP

<output omitted.

Gateway of last resort is not set

192.168.10.0/24 is variably subnetted, 2 subnets, 2 masksC 192.168.10.0/24 is directly connected, GigabitEthernet0/0L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 192.168.11.0/24 is variably subnetted, 2 subnets, 2 masksC 192.168.11.0/24 is directly connected, GigabitEthernet0/1L 192.168.11.1/32 is directly connected, GigabitEthernet0/1 209.165.200.0/24 is variably subnetted, 2 subnets, 2 masksC 209.165.200.224/30 is directly connected, Serial0/0/0L 209.165.200.225/32 is directly connected, Serial0/0/0R1#

.2

.2

Network AddressInterface Address

Network AddressInterface Address

Network AddressInterface Address

53

Verify Interface Configuration

R1# show running-config interface gigabitEthernet 0/0Building 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 autoend

R1#

.2

.2

54

Verifying the R1 Gi0/0 InterfaceR1#show interfaces gigabitEthernet 0/0GigabitEthernet0/0 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 outR1#

55

Verify the R1 Gi0/1 InterfaceR1# show interfaces gigabitEthernet 0/1GigabitEthernet0/1 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 outR1#

56

Verify the R1 Serial InterfaceR1# 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

R1# show ipv6 interface briefGigabitEthernet0/0 [up/up] FE80::FE99:47FF:FE75:C3E0 2001:DB8:ACAD:1::1GigabitEthernet0/1 [up/up] FE80::FE99:47FF:FE75:C3E1 2001:DB8:ACAD:2::1Serial0/0/0 [up/up] FE80::FE99:47FF:FE75:C3E0 2001:DB8:ACAD:3::1Serial0/0/1 [administratively down/down] unassignedR1#

2001:0DB8:ACAD:1::/64:10

:10 :1G0/1

:1S0/0/0

G0/0:1

R1

PC1

PC2

2001:0DB8:ACAD:2::/64

2001:0DB8:ACAD:3::/64

Link Local Address (created automatically)Global Unicast Address (configured)

Link Local Address (created automatically)Global Unicast Address (configured)

Link Local Address (created automatically)Global Unicast Address (configured)

58

Verify the R1 Routing Table

R1# show ipv6 interface gigabitEthernet 0/0GigabitEthernet0/0 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 millisecondsR1#

2001:0DB8:ACAD:1::/64:10

:10 :1G0/1

:1S0/0/0

G0/0:1

R1

PC1

PC2

2001:0DB8:ACAD:2::/64

2001:0DB8:ACAD:3::/64

59

Verify Connectivity

R1# show ipv6 routeIPv6 Routing Table - default - 7 entriesCodes: C - Connected, L - Local, S - Static, U - Per-user Static

<output omitted>

C 2001:DB8:ACAD:1::/64 [0/0] via GigabitEthernet0/0, directly connectedL 2001:DB8:ACAD:1::1/128 [0/0] via GigabitEthernet0/0, receiveC 2001:DB8:ACAD:2::/64 [0/0] via GigabitEthernet0/1, directly connectedL 2001:DB8:ACAD:2::1/128 [0/0] via GigabitEthernet0/1, receiveC 2001:DB8:ACAD:3::/64 [0/0] via Serial0/0/0, directly connectedL 2001:DB8:ACAD:3::1/128 [0/0] via Serial0/0/0, receiveL FF00::/8 [0/0] via Null0, receiveR1#

2001:0DB8:ACAD:1::/64:10

:10 :1G0/1

:1S0/0/0

G0/0:1

R1

PC1

PC2

2001:0DB8:ACAD:2::/64

2001:0DB8:ACAD:3::/64

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Verify the R1 Interface Status

R1# ping 2001:db8:acad:1::10Type 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#

2001:0DB8:ACAD:1::/64:10

:10 :1G0/1

:1S0/0/0

G0/0:1

R1

PC1

PC2

2001:0DB8:ACAD:2::/64

2001:0DB8:ACAD:3::/64

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Tweaking Show Command OutputR1#show ip interface briefInterface IP-Address OK? Method Status ProtocolEmbedded-Service-Engine0/0 unassigned YES unset administratively down down GigabitEthernet0/0 192.168.10.1 YES manual up up GigabitEthernet0/1 192.168.11.1 YES manual up up Serial0/0/0 209.165.200.225 YES manual up up Serial0/0/1 unassigned YES unset administratively down down R1#R1#show ip interface brief | include up GigabitEthernet0/0 192.168.10.1 YES manual up up GigabitEthernet0/1 192.168.11.1 YES manual up up Serial0/0/0 209.165.200.225 YES manual up up R1#

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Tweaking Show Command Output

R1#show ip route | begin GatewayGateway of last resort is not set

192.168.10.0/24 is variably subnetted, 2 subnets, 2 masksC 192.168.10.0/24 is directly connected, GigabitEthernet0/0L 192.168.10.1/32 is directly connected, GigabitEthernet0/0 192.168.11.0/24 is variably subnetted, 2 subnets, 2 masksC 192.168.11.0/24 is directly connected, GigabitEthernet0/1L 192.168.11.1/32 is directly connected, GigabitEthernet0/1 209.165.200.0/24 is variably subnetted, 2 subnets, 2 masksC 209.165.200.224/30 is directly connected, Serial0/0/0L 209.165.200.225/32 is directly connected, Serial0/0/0R1#

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Tweaking Show Command OutputR1#show running-config | section line con line con 0 password 7 110A1016141D loginR1#R1#show ip interface brief | include down Embedded-Service-Engine0/0 unassigned YES unset administratively down down Serial0/0/1 unassigned YES unset administratively down down R1#R1#show ip interface brief | exclude up Interface IP-Address OK? Method Status ProtocolEmbedded-Service-Engine0/0 unassigned YES unset administratively down down Serial0/0/1 unassigned YES unset administratively down down R1#R1#show running-config | begin lineline con 0 password 7 110A1016141D loginline aux 0line 2 no activation-character no exec transport preferred none transport input all transport output pad telnet rlogin lapb-ta mop udptn v120 ssh stopbits 1line vty 0 4 password 7 030752180500 login transport input all!

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Command History FeatureR1#terminal history size 200R1#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 historyR1#

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 of the buffer.

66

67

Routers Operate at Layers 1, 2, and 3 (Decisions made at Layer 3)

68

Remember: Encapsulation

Now, let’s do an example…

Destination IP Address

Source IP Address

Other IP fields

Data

Destination Address

Source Address

Type Data Trailer

Layer 3 IP Packet

Layer 2 Data Link Frame

Current Data Link Address of Host or Router’s exit interface

Next hop Data Link Address of Host or Router’s interface

These change from host to router, router to router, and router to host.

These addresses do not change!

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This is just a summary. The details will be shown next! Now for the details…

Dest. MAC 00-10

Source MAC 0A-10

Type 800

Trailer

Layer 2 Data Link Frame

Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

Data

Layer 3 IP Packet

Dest. MAC 0B-31

Source MAC 00-20

Type 800

TrailerDest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

DataDest. Add FF-FF

Source Add Type 800

Trailer

70

Dest. MAC 00-10

Source MAC 0A-10

Type 800

Trailer

Layer 2 Data Link Frame

Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

Data

Layer 3 IP Packet

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Dest. MAC 0B-31

Source MAC 00-20

Type 800

Trailer

Layer 2 Data Link Frame

Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

Data

Layer 3 IP Packet

RTA Routing TableNetwork Hops Next-hop-ip Exit-interface192.168.1.0/24 0 Dir.Conn. e0192.168.2.0/24 0 Dir.Conn e1192.168.3.0/24 1 192.168.2.2 e1192.168.4.0/24 2 192.168.2.2 e1

RTA ARP CacheIP Address MAC Address192.168.2.2 0B-31

Dest. MAC 00-10

Source MAC 0A-10

Type 800

Trailer

72

Dest. Add FF-FF

Source Add Type 800

Trailer

Layer 2 Data Link Frame

Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

Data

Layer 3 IP Packet

RTB Routing TableNetwork Hops Next-hop-ip Exit-interface192.168.1.0/24 1 192.168.2.1 e0192.168.2.0/24 0 Dir.Conn e0192.168.3.0/24 0 Dir.Conn s0192.168.4.0/24 1 192.168.3.2 s0

Dest. MAC 0B-31

Source MAC 00-20

Type 800

Trailer

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Dest. MAC 0B-20

Source MAC 0C-22

Type 800

Trailer

Layer 2 Data Link Frame

Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

Data

Layer 3 IP Packet

RTC ARP CacheIP Address MAC Address192.168.4.10 0B-20

RTC Routing TableNetwork Hops Next-hop-ip Exit-interface192.168.1.0/24 2 192.168.3.1 s0192.168.2.0/24 1 192.168.3.1 s0192.168.3.0/24 0 Dir.Conn s0192.168.4.0/24 0 Dir.Conn e0

Dest. Add FF-FF

Source Add Type 800

Trailer

74

Layer 2 Data Link Frame

Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

Data

Layer 3 IP Packet

Dest. MAC 0B-20

Source MAC 0C-22

Type 800

Trailer

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The summary once again!

Dest. MAC 00-10

Source MAC 0A-10

Type 800

Trailer

Layer 2 Data Link Frame

Dest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

Data

Layer 3 IP Packet

Dest. MAC 0B-31

Source MAC 00-20

Type 800

TrailerDest. IP 192.168.4.10

Source IP 192.168.1.10

IP fields

DataDest. Add FF-FF

Source Add Type 800

Trailer

Routing Decisions

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Alex Zinin’s Routing Table Principles

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.

I know about my remote networks but it is not my

responsibility if R2 and R3 know about their remote

networks.

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Alex Zinin’s Routing Table Principles

Principle 2: The fact that one router has certain information in its routing table does not mean that other routers have the same information.

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.

???

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Alex Zinin’s Routing Table Principles

Principle 3: Routing information about a path from one network to another does not provide routing information about the reverse, or return, path.

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.

???

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Best Path

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.

Which path is my “best path”?

?

RIP’s metric is hop count

OSPF’s metric is bandwidth

EIGRP is bandwidth + delay

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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.

Equal Cost Load Balancing

To reach the 192.168.1.0/24 network it is 2 hops via R2 and 2 hops via R4.

192.168.1.0/24

?

?

Path Determination of the route

Administrative DistanceIf 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 EIGRP-discovered 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.

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The Routing Table

The Routing TableA routing table is a file stored in RAM that contains information about:

Directly connected routes

Remote routes

Network or next hop associations

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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.

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Interpreting the entries in the routing table.

85

Directly Connected InterfacesA 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 ExampleA routing table with the directly connected interfaces of R1 configured and activated.

87

Directly Connected IPv6 ExampleThe show ipv6 route command shows the ipv6 networks and routes installed in the routing table.

88

Statically Learned Routes

Static RoutesStatic 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.

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IPv4 and IPv6 Routing Protocols

Cisco ISR routers can support a variety of dynamic IPv4 routing protocols including:EIGRP – Enhanced Interior Gateway Routing ProtocolOSPF – Open Shortest Path FirstIS-IS – Intermediate System-to-Intermediate SystemRIP – Routing Information Protocol

Cisco ISR routers can support a variety of dynamic IPv6 routing protocols including:RIPng - RIP next generationOSPFv3EIGRP for IPv6MP-BGP4 - Multicast Protocol-Border Gateway Protocol

93