CCNA-2-CHAPTER-1.docx

CCNA 2 CHAPTER 1

PRIMARY FUNCTIONS OF A ROUTER

ROUTER



Determine the best path to send packets

Router - connects one network to a nother network.



Forward packets toward their destination

- The router is responsible for the delivery of packets across different networks. - uses routing table: to determine the best path to

PACKET FORWARDING MECHANISMS

Process switching - each packet must be



use to forward a packet - if different IP networks, router forwards packets to

processed by the CPU individually. Fast switching - first packet of a flow is



the default gateway.

process-switched and added to the fast-

CHARACTERISTICS OF A NETWORK

switching cache. Cisco Express Forwarding (CEF) - builds the

 

Topology

FIB and adjacency tables. Preferred



Speed

mechanism for cisco routers.



Cost



Security



Availability



Scalability



Reliability

DEFAULT GATEWAY

-

if sending packets is of the same network: packet is sent from host interface

-

if different networks: packet is sent to default gateway

ROUTERS ARE COMPUTERS

Cisco IOS (Internetwork Operating System)  –



local network.

operating system of cisco routers. 

ROUTER MEMORY 

Subnet mask - Identifies with which

network subnet the host can communicate.

Volatile Memory  – temporary storage 

IP address - Identifies a unique host on a

Random Access Memory (RAM)



Default gateway - Identifies the IP address

- Running IOS

of the router to send a pack et to when the

- Running configuration file

destination is not on the same local

- IP routing and ARP tables

network subnet. - also used to connect

- Packet buffer 

local network to internet

Non-volatile Memory  – permanent storage 

Read-only memory (ROM) - Bootup instructions

Gateway of last resort - A router is also usually

- Basic diagnostic software

configured with its own default gateway.

- Limited IOS in case the router cannot load the full featured IOS 

Non-Volatile Random Access Memory (NVRAM)



DOCUMENT NETWORK ASSIGNING 

Topology diagram - Provides a visual

- Startup configuration file

reference that indicates the physical

Flash

connectivity and logical Layer 3 addressing.

- IOS

Often created using software, such as

- Other system-related files

Microsoft Visio.



An addressing table - A table that captures

device names, interfaces, IPv4 a ddresses, subnet masks, and default gateway addresses. 

Secure management access



Configure a banner

ENABLE IP ON HOST Statically - manually assigned IP

- used to identify specific network resources such as servers/printers. - can be used in small networks with little number of hosts. Dynamically - automatically obtained IP address. IP

address from DHCP Server DEVICE LEDs

-

Indicates the status of the router

-

green led : good connections

-

blinking led : denotes network activity



1 blink + pause  – port operating at 10 Mb/s



2 blink + pause  – port operating at 100

copy run start  – to save changes in a router CONFIGURE IPv4 ROUTER INTERFACE

- configure IP address and subnet mask - no shutdown: to enable interface - clock rate: to configure serial interface CDE

Mb/s 

1 blink + pause  – port operating at 1000

CONFIGURE IPv6 ROUTER INTERFACE

Mb/s

- same as configuring ipv4 but uses “ipv6” in terminal instead of “ip”

CONSOLE ACCESS

-

required when initially configuring a device,

- still uses no shutdown for activation 

IPv6 supports more than one address - Global unicast address

or if remote access (SSH and HTTP) fails.

- EUI-64: low order bits - link local

Console cable - RJ-45-to-DB-9 serial cable or a USB

serial cable

CONFIGURE THE LOOPBACK0 INTERFACE

Terminal emulation software - Tera Term, PuTTY,

HyperTerminal

- is a logical interface internal to the router. It is not assigned to a physical port. - interface is always up , no need for “no

ENABLE IP ON SWITCH

shutdown”

- IP addressed is configured virtually via

- used for testing

switched virtual interface (SVI) CONFIGURE BASIC ROUTER SETTINGS

- multiple loopback addresses can be enabled. VERIFY INTERFACE SETTINGS 



Name the device

show ip interface brief - Displays a

summary for all interfaces

show ip route - Displays the contents of the



4.

the device issues and ARP request

IPv4 routing table stored in RAM. 5. show running-config interface interface-id -



Routers de-encapsulates the frame and determines the destination MAC address

Displays the commands configured on the

from the given IP address.

specified interface. For IPv6, commands are also the same with IPv4

If the next hop MAC address is unknown,

ROUTING DECISIONS

The routing table search results in one of three path determinations:



show ipv6 interface brief 



show ipv6 route



show ipv6 interface

destination IP address of the packet belongs



ping

to a device on a network that is directly



Directly connected network - If the

connected to one of the interfaces of the

FILTER SHOW COMMAND OUTPUT

router, that packet is forwarded directly to Use the ‘terminal length ’



the destination device.

command to specify the number of lines to be displayed.



address of the packet belongs to a remote

To filter out specific output of commands,



network, then the packet is forwarded to

use the “|” pipe character.

another router.

Can use parameters to filter: section,



include, exclude, and begin



No route determined - If the destination IP

address of the packet does not belong to

show history – captures last 10 lines in the history

either a connected or remote network, the

buffer

router determines if there is a Gateway of Last Resort available. If there is a default

ROUTER SWITCHING FUNCTION

-

Remote network - If the destination IP

route, the packet is forwarded to the

which is the process used by a router to

Gateway of Last Resort. If the router does

accept a packet on one interface and

not have a default route, then the packet is

forward it out of another interface. PACKET SWITCHING

discarded. BEST PATH

- the best path to a network is the path with the lowest metric. - metric is the value used to measure the distance to a given network 

Routing Information Protocol (RIP) - Hop

count 1.

In sending packets from PC 1 to PC 2, the source IP address is of PC1 and destination

2.

Open Shortest Path First (OSPF) - Cisco’s

IP address is of PC2.

cost based on cumulative bandwidth from

The IP address does not change in the data,

source to destination

instead when forwarded, the MAC address changes 3.



Switch are not considered as destination sources but only routers and end devices.



Enhanced Interior Gateway Routing Protocol (EIGRP) - Bandwidth, delay, load,

reliability

ADMINISTRATIVE DISTANCE



address of the remote network.

- represents the "trustworthiness" of the route; the lower the AD, the more trustworthy the

Destination network - Identifies the



route source.

Administrative distance - Identifies the

trustworthiness of the route source. Lower values indicate preferred route source. 

Metric - Identifies the value assigned to

reach the remote network. Lower values indicate preferred routes. 

Next-hop - Identifies the IPv4 address of the

next router to forward the packet to. 

Route timestamp - Identifies how much

time has passed since the route was learned.

ROUTING TABLE 

Directly connected routes - These routes



Outgoing interface - Identifies the exit

come from the active router interfaces.

interface to use to forward a packet toward

Routers add a directly connected route

the final destination.

when an interface is configured with an I P address and is activated. 

Remote routes - These are remote

networks connected to other routers. Routes to these networks can either be statically configured or dynamically learned through dynamic routing protocols. routing table - is a data file in RAM that is used to

DIRECTLY CONNECTED INTERFACES

store route information about directly connected

- considered up when:

and remote networks.

1. assigned valid IP address 2. no shutdown command

ROUTING TABLE SOURCES

Routing Table Entries: 

Local Route interfaces



Directly connected interfaces – interfaces – activated

3. receive carrier signal from other devices (switch, router, host) DIRECTLY CONNECTED ROUTING TABLE ENTRIES 

Route source - Identifies how the route was

learned. Directly connected interfaces have

with no shutdown

two route source codes. ‘C ‘ C’ identifies a



Static routes – routes – manually configured



Dynamic routing protocol - dynamic routing

the IPv4 address assigned to the router’s

protocols (EIGRP, OSPF)

interface.

REMOTE NETWORK ROUTING ENTRIES

directly connected network. ’ L’ identifies



Destination network - The address of the

remote network. 

Route source - Identifies how the route was

learned.

Outgoing interface - Identifies the exit





RIPng (RIP next generation)



OSPFv3



EIGRP for IPv6

interface to use when forwarding packets to the destination network.

STATIC ROUTES

- added after directly connected interfaces are added - are manually configured. Benefits are improved security and resource efficiency - disadvantage: lack of automatic configuration when topology changes. Two types of Static Routes: 1. Static route to a specific network Router(config)# ip route network mask{ next-hop-ip | exit-intf   }  }

2. Default static route Router(config)# ip route 0.0.0.0 0.0.0.0 { exit-intf  0.0.0.0 {  | next-hop-ip }  |

DYNAMIC ROUTING

- Dynamic routing protocols are used by routers to share information about the reachability and status of remote networks. - automatically share routing information with other routers and compensate for any topology changes without involving the network administrator. Dynamic IPv4 routing protocols supported by Cisco 

EIGRP - Enhanced Interior Gateway Routing

Protocol 

OSPF - Open Shortest Path First



IS-IS - Intermediate System-to-Intermediate

System 

RIP - Routing Information Protocol

Dynamic IPv6 routing protocols supported by Cisco