CCNA Basics Part-2

How to assign an IP address to the Router and configure it?

Router(config)# interface ethernet 0 /0  or  serial 0/0
Router(config-if)ip address <IP address> <Subnet Mask>
Router(config-if)no shutdown

 We assign our default-gateway as the IP address to the ethernet port.

 When the router is switched ON, by default all the interfaces are administratively down. To make the interfaces up we give no shutdown command.

Why and where we use the clock rate?

The serial line has two ends DTE and DCE. This line goes up and down when IP address and no shutdown is configured on both sides and will be in asynchronous state always. To synchronize the link clock rate should be configured at DCE end.

How to find out the DCE end?

Router#sh controllers serial 0/0

Difference between Request timed out Destination host unreachable

Syntex of the command to be used:

Reply from <ip address> : <byte= > time<xms TTL=xxx

Request timed out

When the packet is lost in transition, we will get “request timed out” message.
Destination host unreachable

If the host doesn’t know the route to the destination - “Destination unreachable” message is displayed i.e., the specified address is not present in the routing table

Reply from <ip address> : <byte= > time <xms TTL=xxx
Reply from the destination indicates that the connection exists

Time To Live (TTL) – a field in an IP header that indicates the no. of routers (hops) the packet can cross. TTL for systems is 128 and for routers it is 255. If the destination is not reached before the TTL expires, then the packet is dropped. This stops IP packets from continuously circling around in the network looking for a home

CCNA Fundamentals (Basics)

Troubleshooting commands of Networking 

1. Ping loopback
2. Ping NIC
3. Ping default gateway
4. Ping remote device

Windows DOS Troubleshooting Commands

ping 127.0.0.1
tracert
ipconfig/all
arp -a

Cisco IOS Troubleshooting Commands

ping 127.0.0.1
traceroute

IP CLASSESS:

Class A - 1-126 - network.node.node.node
Class B - 128-191 - network.network.node.node
Class C - 192-223 - network.network.network.node

Private Address Range

Class A - 10.0.0.0 - 10.255.255.255
Class B - 172.16.0.0 - 172.31.255.255
Class C - 192.168.0.0 - 192.168.255.255

OSI Model 

Application - Identifying and establishing the availability of intended communication partner and
whether there are sufficient resources

Presentation - Data translation, encryption, code formatting

Session - Setting up, managing and tearing down sessions. Keeps application’s data separate

Transport - Provides end-to-end transport services - establishes logical connections
between hosts. Connection-oriented or connectionless data transfer.

Network - Manages logical addressing and path determination

Data Link - Provides physical transmission of data, handles error notification, flow
control and network topology. Split into two sub layers (LLC and MAC)

Physical - Specifies electrical, mechanical, procedural and functional requirements for activating, maintaining
and deactivating a physical link.

Cisco 3-Layer Hierarchical Model

Core - Backbone connectivity , common for all users, needs to be as fast as possible and fault tolerant, avoid ACL, VLAN trunking and packet filtering

Distribution - Routing - provides access control policies, filtering, WAN access and VLAN trunking

Access - Switching - User and workgroup access, segmentation

OSI Model vs. TCP/IP Model

Process/Application layer

FTP - TCP file transfer service – port 20-21
Telnet - Terminal emulation program – port 23
TFTP - UDP file transfer – port 69
SMTP - Send email service – port 25
DHCP – Assigns IP addresses to hosts –ports 67 and 68
DNS – Resolves FQDNs to IP addresses –port 53

Host-to-Host layer

TCP - Connection-oriented protocol, provides reliable connections
(acknowledgments, flow control, windowing)

UDP - Connectionless protocol, low overhead but unreliable
TCP/IP Model Protocol Suite Internet layer
IP - connectionless protocol, provides network addressing and routing
ARP - finds MAC addresses from known IPs
RARP - finds IPs from known MAC addresses
ICMP - provides diagnostics, used by ping and traceroute Network Access

CIDR BASICS

255.0.0.0 /8
255.128.0.0 /9
255.192.0.0 /10
255.224.0.0 /11
255.240.0.0 /12
255.248.0.0 /13
255.252.0.0 /14
255.254.0.0 /15
255.255.0.0 /16
255.255.128.0 /17
255.255.192.0 /18
255.255.224.0 /19
255.255.240.0 /20
255.255.248.0 /21
255.255.252.0 /22
255.255.254.0 /23
255.255.255.0 /24
255.255.255.128 /25
255.255.255.192 /26
255.255.255.224 /27
255.255.255.240 /28
255.255.255.248 /29
255.255.255.252 /30