InterVLAN routing (Multilayer Switch)

Introduction

A Multilayer switch also known as a Layer 3 switch is a device that performs the function of a switch as well as a router also. The multilayer switch has the ability to operate at higher layers.  It can perform both Layer 2 and layer 3 functions at extremely fast speed. This is also a great option for us if we want to perform InterVLAN routing. In a Multilayer Switch, the VLAN interface acts as a router interface having an IP address and a subnet mask. The configuration of a multilayer switch is very easy and simpler as compared to a Router-On-A-Stick(ROAS).

Now take 2 PC's and a MultiLayer switch and connect it using a straight cable. Connect PC1 with interface fa 0/3 and PC2 with interface fa 0/5.

Now the first step is to vlan 3 and vlan 5 and assign vlan's to interfaces fa 0/3  and fa 0/5

switch(config)# vlan 3
switch(config-vlan)# name vlan03
switch(config-vlan)# exit
switch(config)# vlan 5
switch(config-vlan)# name vlan05
switch(config-vlan)# exit
switch(config)# interface fa 0/3
switch(config-if)# switchport mode access
switch(config-if)# switchport access vlan 3
switch(config-if)# exit
switch(config)# interface fa 0/5
switch(config-if)# switchport mode access
switch(config-if)# switchport access vlan 5

Now after you have made access ports to interfaces, it's time to assign IP address to vlan 3 and vlan 5

switch(config)# interface vlan 3
switch(config-if)# ip address 192.168.3.1 255.255.255.0
switch(config-if)# exit
switch(config)# interface vlan 5
switch(config-if)# ip address 192.168.5.1 255.255.255.0
switch(config-if)# exit

The last command helps to perform routing in a multilayer switch. Without this command, the packets cannot be routed in a multilayer switch.

switch(config)# ip routing

Now we assign IP adresses to PC1 and PC2 as shown below

Note that the default gateways of both the PC's contains the same IP address that we have given to VLAN interfaces. Now if we ping PC2 from PC1, we get the reply.

Introduction to DHCP Part 2

DHCP Configuration

The DHCP is configured on a router. We then also state that router as a DHCP server. Remember that from a subnet, you must assign DHCP lease range that starts from .101 till .254 ( for example like 192.168.0.101 till 192.168.0.254). The range till 100 is used for static IP addressing such as those IP addresses that are given to switches, gateways, VLAN's, DNS servers etc. This is a standard way for using DHCP and is performed by many companies in the world.

To enable dhcp server you must write the following command on the router :
Ip dhcp pool name of pool

DHCP server settings

Following are the settings that we need to make on a DHCP server .
 
The subnet ID and the mask
The DHCP server needs to know all the addresses in the subnet.

Reserved addresses
Addresses that are reserved or excluded from the DHCP server which are needed to be used for static IP addressing. The command that is used for reserved addresses is :
ip dhcp excluded-address lowest address highest address

Default-router
The IP address of the router which is being used on that subnet.

DNS IP address
The IP address which is giving to a DNS server in the network.

Now take 2 PC's, 1 switch and 1 router. Connect the PC's and router with the switch using a straight cable as shown below

Now for the configuration
Router(config)# ip dhcp pool network
Router(dhcp-config)# network 192.168.5.0 255.255.255.0
Router(dhcp-config)# default-router 192.168.5.1 
Router(dhcp-config)# dns-server 192.168.5.5
Router(dhcp-config)# exit

Now again go to config mode so we can write the command for reserve static IP addresses

Router(config)# ip dhcp excluded-address 192.168.5.1 192.168.5.100

Now go to router interface 0/0 and assign the IP address to the interface which you have also given to the default router in the DHCP settings too.

 Router(config)# interface fa 0/0
 Router(config-if)# ip address 192.168.5.1 255.255.255.0
 Router(config-if)# no shutdown

Now go to PC1 and PC2 and click on DHCP in IP configuration

You can see that the IP address, subnet mask, default gateway and DNS server has been assigned dynamically by the DHCP successfully.

 

Introduction to DHCP Part 1

Introduction

Dynamic Host Configuration Protocol (DHCP) is the most commonly used protocol in the TCP/IP network. Suppose you are a network engineer in company and you have to assign IP address to 50 PC's of a department. Instead of assigning static IP address to each PC, You can assign them IP addresses from an IP Pool using a DHCP server. The configuration of host IP settings sits in a DHCP server. The client learn these settings using DHCP messages. DHCP assigns a temporary lease of IP addresses to the host for a temporary period of time. When the time expires, the host is then assigned with a new IP Address. When  a device is removed from the network, the server reclaim the IP addresses and assign it to someone else or save it for the future.

The DHCP Process uses four types of messages to assign an IP address to a DHCP Client

1. Discover
2. Offer 
3. Request
4. Acknowledge 

Discover
It is sent by a DHCP client to discover a DHCP server to claim an IP address.

Offer
The offer for an IP address lease is sent to the client by a DHCP server and also inform the client of it's other information and parameters.

Request
The DHCP client then sends the request to the DHCP server for the IP address lease which has been sent in the offer message.

Acknowledge
The DHCP server then assign the address and also lists the DNS server IP addresses, mask and the  default router.

IPv4 Special Address

There is a somewhat a problem with the DHCP client that they don't have an IP address yet to communicate with a DHCP server so there are two special IPV4 address that helps them to solve this problem.

0.0.0.0 : This is an address that is reserved to the host who don't have an IP address yet .

255.255.255.255: It is known as  The Local Broadcast Address. The Packets that are sent to this destination address are broadcasted on the Local data link but the routers will not forward them.

Allocation modes

DHCP server uses three allocation modes

• Dynamic Allocation ( refers to the DHCP configuration which I will show you in the next part).
• Automatic Allocation ( we can set the DHCP time to infinite).
• Static Allocation  ( Configuring a specific IP address for a host based on the host's MAC address).

In the next part, we will learn the DHCP configuration for Dynamic Allocation.

Administrative distance, Passive Rip and other terminologies

Administrative distance

suppose a router sees two multiple path going the the destination router direction.

It can see both the paths as best path because of multiple routing protocols running on the router. Sometimes even the metric count can't help us to choose the best path and still the router needs to choose single best path. To solve this problem each routing protocol has been assigned a different numeric value. Due to that numeric value, the router then chooses the routing protocol with the lowest numeric value. That value is known as the Administrative Distance (AD).

Following are the distance of the following protocols

• Connected routes (AD=0)
• Static routes (AD=1)
• EIGRP routes (AD=90)
• OSPF routes  (AD=110)
• RIP routes (AD=120)
• DHCP  (AD=254)

PASSIVE RIP
This Passive command helps to stop RIP updates being advertised to the interface. Configuration is shown below

Router(config)#router rip
Router(config-router)#Passive-interface g0/1

You have to activate the command on the interface which you don't want to advertise.

Load balancing
Suppose a router have find two paths with the same metric, so it sends some packets over one path and some to another path. This is known as Load -Balancing.

Contigous Network 
A contigous network is that topology in which a subnet of one network is not separated by a subset of classful network.

Discontigous Network
a discontigous network is that topology in which a subnet of one network is  separated by a subset of classful network.

No Autosummary
when older classful routing protocols were used in the early networking era, a cautios subnet design  was used to avoid discontigous classful network. The no autosummary command on every router of the topology helps to avoid this problem.

Routing Loop
When a set of routers that causes a packet which has been sent to there paths happens to be keep looping between them and never arrived to the destination. That status is known as Routing Loops.

Split Horizon
Split Horizon is a process that  helps to avoids routing loops. It has a distance vector feature that tells the router to discard/omit some routes from an update sent by some interface.

Route Poisoning: 
Route poisoning advertises a field to other routers with a special numeric value known as the infinite value.A Router consider those router as failed because of the infinite metric.

Routing Information Protocol

Routing Information Protocol (RIP) is one of the most used protocols in network. It is used for routing packets between routers. The version using nowadays is called RIPv2, though there is a new version known as RIPng (ng stands for the Next Generation) which may be used mostly for IPv6. After getting active on a router, the router performs three basic functions which are as follows :

1. Router sending routing updates on the interfaces. 
2. The router listens and then processes incoming updates on that same interface.
3. The router advertises the connected subnets to the interface. 

The features of RIPv2 are as follows:

• It is password authenticated. 
• It creates the summary of routing table. 
• It can also be used for multicast address.
• It supports VLSM (Variable Length Subnet Mask) also.

Take three routers, three switches and three PC's. Connect the router with each other on there serial interface 2/0 and 3/0 using a serial cable. Then Connect each PC with a switch and each switch with the router on the interfaces 0/0 and 1/0 using a straight cable as shown below.

For configuration, we need to use router rip command on config mode and also choose version 2 for RIP. Following are the IP's and gateways we need to assign to PC's.

Now assign IP's to those interface which you will use as gateways . the IP's to be assign to router ethernet interfaces and serial interfaces.

In Router 0
fa 0/0 192.168.3.1
se 2/0 192.168.9.2
se 3/0 192.168.10.2

In Router 1
fa 0/0 192.168.5.1
se 2/0 192.168.9.1
se 3/0 192.168.11.2

In Router 2
fa 0/0 192.168.7.1
se 2/0 192.168.10.1
se 3/0 192.168.11.1

Following is the configuration for RIPv2

On Router 0
router(config)# router rip
router(config)# version 2

router(config)# network 192.168.3.0
router(config)# network 192.168.9.0
router(config)# network 192.168.10.0

On Router 1
router(config)# router rip
router(config)# version 2

router(config)# network 192.168.5.0
router(config)# network 192.168.9.0
router(config)# network 192.168.11.0

On Router 2
router(config)# router rip
router(config)# version 2

router(config)# network 192.168.7.0
router(config)# network 192.168.10.0
router(config)# network 192.168.11.0

Now if you ping pc1 to pc0 or pc2, you will get the reply :

To see the the routing table just write the command "show ip route", you will see the table as shown below

The lines which are starting with the symbol R shows the RIP connected routes.

InterVLAN routing (Router-On-A-Stick)

                                          Router-On-A-Stick

Now consider yourself again as a network engineer in a bank. This time the scenario is that your treasury department, finance department and human resource are on the same switch. Now we know that the switch broadcast packets to all the ports, so if someone from the treasury department sends a packet to the finance department, it will be broadcasted to the human resource department also. Even if you put both the departments in a different Vlan together, still the packets will not be forwarded to the destination rather than broadcasted to all interfaces which we don't want. The forwarding of packets from source to destination is the job for a router. The process of forwarding packets between VLAN's is called InterVLAN routing. For forwarding packets, you need to connect the switch with the router. This feature is also known as Router-On-A-Stick.

Now take three pc's and a router and connect it with a switch. Connect the router with interface 0/1 and connect the pc's with interface 0/3 and 0/5 as shown below.

Now go to the switch and create vlan 3 and vlan 5.

switch(config)# vlan 3
switch(config-vlan)# name vlan03
switch(config)# vlan 5
switch(config-vlan)# name vlan05
switch(config-vlan)# exit

Now assign vlan 3 to interface fa 0/3 and vlan 5 to interface fa 0/5 and made fa 0/1 trunk port between the switch and router.

switch(config)# interface fa 0/3
switch(config-if)# switchport mode access
switch(config-if)# switchport access vlan 3
switch(config-if)# exit
switch(config)# interface fa 0/5
switch(config-if)# switchport mode access
switch(config-if)# switchport access vlan 5
switch(config-if)# exit
switch(config)# interface fa 0/1
switch(config-if)# switchport mode trunk
switch(config-if)# exit

Now you need to assign ip's to vlan 3 and vlan 5.

switch(config)# interface vlan 3
switch(config-if)# ip address 192.168.3.2 255.255.255.0
switch(config-if)# no shutdown
switch(config)# exit
switch(config)# interface vlan 5
switch(config-if)# ip address 192.168.5.2 255.255.255.0
switch(config-if)# no shutdown
switch(config)# exit

Now the work of the switch has been completed. Lets move on to the router. Now here we need to create subinterfaces for trunking to forward packet between VLAN's and we will use dot1q trunking. The command will be "encapsulation dot1q vlanid ".

router(config)# interface fa 0/0.1
router(config-subif)# encapsulation dot1q 3
router(config-subif)# ip address 192.168.3.1 255.255.255.0
router(config)# interface fa 0/0.2
router(config-subif)# encapsulation dot1q5
router(config-subif)# ip address 192.168.5.1 255.255.255.0
router(config)# interface fa 0/0
router(config-if)# no shutdown

The "no shutdown " command on interface fa 0/0 helps to active the port. Now assign IP's and gateways to both PC's as shown below :

Hence if you ping  the treasury department to finance department, you will get the reply as shown  below

 

Port Security in Switch Part 2

Port Security Configuration

Take a switch and connect three PC's and one switch on the switch's port Fa 0/1 - Fa 0/4 as shown below

Now on interface Fa 0/1, we will perform the following configuration

switch# interface fast ethernet 0/1
switch# switchport mode trunk
switch# switchport port-security
switch# switchport port-security maximum 1

On fa 0/1, we have assign the maximum number for devices that can be connected on this port. So if the maximum no reached past it's limit the port will get disable as shown below

Now on interface fa 0/2, we will perform the following configuration

switch# interface fast ethernet 0/2
switch# switchport mode access
switch# switchport port-security
switch# switchport port-security maximum 1
switch#  switchport port-security violation shutdown

On fa 0/2, we have assign violation rule which is shutdown. Whenever a port-security is breached ,  the violation action performs it's function .There are three types of actions for violation :

• Protect 
• Restrict
• Shutdown

Now on interface fa 0/3, we will perform the following configuration

switch# interface fast ethernet 0/3
switch# switchport mode access
switch# switchport port-security
switch# switchport port-security mac-address 0001.420C.83EA

On fa0/2, you can see that we have assigned a static MAC address but port detected another MAC address which is a clear violation and has been shutdown as shown below

 

Now on interface fa 0/4, we will perform the following configuration

switch# interface fast ethernet 0/4
switch# switchport mode access
switch# switchport port-security
switch# switchport port-security mac-address sticky
  
On fa0/4, we have configured the sticky command which will dynamically take the mac address from the first device that gets connected on that port.

Now remember to enable a port again that has been disabled, you need to manually disable the port by using the "shutdown" command and then enable it with "no shutdown" command. 

To see the port-security status of any interface, the command is "show port-security interface". The status of fa 0/1 has been shown below.

 

Port Security in Switch Part 1

Port Security

Introduction
Suppose your I.T head asks you to connect only the known list of users in a switch in your I.T so no other users from another depart comes and connect there device with your switch. That's where the concept of port security helps you to solve this problem. Through port security, inappropriate device cannot connect with your switch which makes the switch more secure. The identification of the devices are made by the device's MAC address because the switch only understands the MAC address but not the device's IP address.

Features of Port Security

The features of port security are as follows:

• The switch keeps a list of all incoming frames from all the source's MAC address .
• The switch helps you to define the maximum no of MAC address which should have access through that port.
• If the no of MAC addresses reached the configured maximum limit, it gives the detection of port security violation.
• There is a command called sticky MAC address which helps the port security to learn the MAC address of the devices dynamically so that you should not carry the burden of writing address of all devices with your hands.

This is an important note that you should keep in your mind which is "Whenever you put port security on a port of a switch, the switch will no longer any MAC address as a dynamic entry. Now we know that to see the mac address entries in a switch you use the command "show mac address" but this command will not work on ports that uses port security. There are two commands that help  you to see MAC addresses of secure ports which are as follows

• Show mac address-table secure: This command shows the mac address list of those ports that uses port security.
• Show mac address-table static: This command shows the mac address list of those ports that are statically assigned by the host.

In the next post post we will learn the configuration of port security and also the show commands that have been listed above.

Switch interface status and duplex/speed synchronization

Troubleshooting is a very important in a career of a network engineer. If a network of the company in which you are working goes down you must have the ability to perform troubleshoot and fix problems so your network quickly comes back online and the company resume it's work. In this post we will talk about troubleshooting in switches.There are many features you need to analyze on switches in which some are shown below :

• Checking Interface status and statistics
• Pattern of forwarding frames
• Synchronization of speed and duplex
• Examining port security
• Configuration of VLAN and VLAN trunking

When you use the command of show interface status in switches, The command shows two types of status which is the Line status and the Protocol status. The line status refers to the layer 1 (Physical Layer) status condition and the protocol layer gives us the layer 2 (Data Link Layer) status condition. The line and protocol status can be in an up state, down state or administratively down
(manually done by the host) state. Below are the combination status and causes made by both the status

Line Status         Protocol status         Interface                 Causes

1. up                                      up                   connected                 The interface is working
2. down                                 down                disabled                    Disabled by port security
3. up                                     down                not connected            Not expected on switch
4. down                                 down                not connected            Bad cable or wrong pinouts
5. administratively down          down                disabled                    Done by the user manually

                                                                                                              
Duplex and Speed 
We all know what is speed of a  network but most of you are not familiar with duplex .There are two types of duplex:

• Full duplex : The switch can send and receive at the same time.
• Half duplex : The switch cannot send and receive at the same time.

Now remember, the speed and duplex of the switch and the user end devices must be same. Suppose the pc is sending data at 100mbps but the switch speed is just 10 mbps. The link won't work because the speed must be the same. Same isthe condition for duplex that both the devices must have the same duplex mode.There is a command called "Auto-negotiation" which helps us to solve this problem.

In any case,if the auto-negotiation setting fails on a switch or a user end device, it then uses default settings which are

• Speed :Use the slowest supported speed (mostly 10mbps).
• Duplex: If 10 or 100 mbps, use half duplex otherwise it will use full duplex.

In the next post, we will learn about the port security which is an important part of a switch in terms of security and troubleshooting.

Virtual Local Area Network (VLAN) Trunk

Again consider a scenario of being a network engineer in a bank.The Treasury department and  the Procurement department are on two different LAN's meaning they are connected to two separate  switches. So now your boss wants you to make a separate domain which includes both department. Now you cannot just take both switches and started putting both departments cables in one which would obviously disturb the bank activities.Instead what you will do is that you are going to connect both switches with each other and then you assign both the department to a separate VLAN with both having the same VLAN number and use a concept called VLAN Trunking which will help them to communicate with each other even being on a separate domain. Now I will show you how to perform VLAN trunking in Cisco Packet Tracer.

Open your Cisco Packet Tracer. Take 4 PC's and 2 switches and connect 2 PC's with one switch using a straight cable on interface 0/3 and 0/5. Same process is for the remaining PC's and switch also and connect them with interface 0/3 and 0/6. Now connect both switches with each other using both interfaces 0/1 with a crossover cable. Assign APIPA IP to all PC's by going to the IP configuration and clicking on DHCP. Name the PC which are on fa 0/3 as Treasury and Procurement and name the rest PC's as Finance and Logistics.

Now if you have read my previous post you must know how to make VLAN and assign them to interfaces. if you haven't then go to my blog and read the post Virtual Local Area Network (VLAN).
Now for switch0, create VLAN 3 and VLAN 5 and assign VLAN 3 to interface 0/3 and VLAN 5 to interface 0/5.Then in Switch1, create VLAN 3 and VLAN 6 and assign VLAN 3 to interface 0/3 and VLAN 6 to interface 0/6. Now ping any PC with each other other and you will see that the reply is not coming so the VLAN's are created perfectly. Now our main task is to make communication between the Treasury and the Procurement depart through VLAN trunking. Now go to switch0 and do the following configuration in config mode

switch(config)#interface fastethernet 0/1
switch(config-if)#switchport mode trunk 
switch(config-if)#exit

Your VLAN trunking is now enabled and now you can send packets from the treasury to the procurement department even being in a separate domain.

if you want see that trunking is enabled, write the command "show interface trunk" on privileged mode and you will see the trunk status.

Virtual Local Area Network (VLAN)

Consider the scenario. You are working in a bank as a network engineer. The bank ask you to make a separate domain for the treasury department and finance department so they could not communicate with each other. Now, the treasury department consist of 10 users and the finance department consist of 5 users. Now to separate there domain you need to buy one switch for each department which will be expensive. Now instead of buying different switches from different department you can separate the department's domain using a single switch. The concept of separating  LAN's in a single domain is called Virtual Local Area Network (VLAN's).

Now open your Cisco Packet Tracer and connect 4 workstations with a switch using a straight cable. Consider 2 pc's of treasury department with interface fa0/1 and fa0/2 and 2 pc's of finance department with interface fa0/3 and fa0/4. Assign APIPA IP's to each pc. Click on the pc then go to the IP configuration and click on DHCP.

Now go to pc0 of treasury department's command prompt and write the command ping and the IP of PC 3 which is in finance department.It will give the reply because the treasury department and the finance department are on the same domain.

Now to separate these depart we will use VLAN's. Note that one vlan contains only one domain. Now go to the switch and create 2 VLAN.

Switch>en

Switch#config t

switch(config)#Vlan 2

switch(config-vlan)#name Vlan02

switch(config)#Vlan 3

switch(config-vlan)#name Vlan03

After you have created Vlan's we will go to the port(interface) config mode of those interfaces through which the pc's are connected. The treasury department port's are fa0/1 and fa0/2 and the finance department port's are fa0/3 and Fa0/4. Assign vlan 2 to treasury department and vlan 3 to finance department if you are assigning VLAN's to multiple ports then you don't have to access single port at a time to assign VLAN's. Instead use the "interface range" command to access multiple port and giving same configuration to all at a same time.

Switch>en

Switch#config t

switch(config)#

switch(config)#interface range fa0/1-fa0/2`

switch(config-if-range)#switchport mode access

switch(config-if-range)#switchport access vlan 2

switch(config)#interface range fa0/3-fa0/4

switch(config-if-range)#switchport mode access

switch(config-if-range)#switchport access vlan 3

switch(config-if-range)#exit

Now again go to pc01 and command prompt and ping pc03. This time the pc will not reply because it is on the separate domain.This means that you have configured the VLAN's correctly.remember all ports of the switch are already assigned to default VLAN which is VLAN 1.To see your VLAN status write the command on "show vlan brief" where you can see VLAN information.

                                                                                                                                                                     

Data Link Protocols and Ethernet WAN description

HDLC Basics

Every data Link Protocol has one basic job to perform which is to control the correct delivery of every data that been sent over a physical medium.When a packet is encapsulated in a Data Link Frame, it also gave the packet a header and a trailer. The trailer consist of a FCS(Frame Check Sequence) Field which make sure that the frame which has been delivered has no errors and has arrived correctly. HDLC (High-Level Data Link Control) as a Data link Protocol also provides this function.

When we send a HDLC frame through a router, it can only go to one place which is the the other end of the link. The HDLC contains the following fields which are :

• Flag
• Address
• Control 
• Type 
• FCS

PPP (Point-To-Point) Data Link Protocol

The PPP is an another most important used Data link protocol. It is mostly used for the connection of synchronus and asynchronus circuits. It is also used as a DSL(Digital Subscriber Line) internet service for customers.

There are two types of PPP derivatives which are as follows:

1. Point-To-Point over Ethernet(PPPoE)
2. Point-To-Point over ATM (PPPoA)

Ethernet as a WAN

During the beginning of the Internet age, The Ethernet was only appropriate for deployment in LAN's.The restrictions on cable lengths was one of the limit as the ethernet can only go as far as 100m. But as the passage of time, The IEEE improved Ethernet standards in every way so that the Ethernet can be use as a WAN technology. 

There are two types of Ethernet WAN's

1. Ethernet Emulation
2. EoMPLS (Ethernet over Multi Protocol Label Switching)

The Ethernet emulation is used as a general term to tell that the service acts like one Ethernet link. The EoMPLS is a technology that is used on a SP (Service Provider) Cloud. The EoMPLS service provides a point-to-point connection between two customer devices and shows the type of connectivity as if a fiber Ethernet link exists between the two customer devices.

For any queries or problems related to my tutorials please email me on shahzeb.h23@gmail.com

WAN Technology Description

The LAN (Local Area Network) typically include Nearby devices but when we talk about WAN (Wide Area Network), we are literally talking about devices that can be Far apart. The main priority for WAN is to move data between LAN's. The device which is used to connect the WAN with LAN is called a Router.
To connect our LAN with WAN, we order a Leased Line which is provided to us by an ISP (Internet Service Provider). Leased Line is available in variety of speed. The Leased Line is known by many names like Leased Circuit, Serial Line/Link, P2P Line/Link, T1, WAN Line/Link and Private Line. For connecting a Leased Line on a site, The site requires a CPE (Customer Premises Equipment) which consist of :

• A Router
• Serial Interface Card
• CSU/DSU (Channel Service Unit/Data Service Unit)                                       

The Serial cables that are used between a router and an external CSU/DSU are DTE (Data Terminal Equipment) and DCE (Data Communication Equipment). DTE has a male connector while DCE has a female connector which helps to connect both cables directly. The DCE cable works like a crossover cable because it swaps the transmitting and recieving pairs.
The DCE cables help the CSU/DSU to perform one primary Function which is called CLOCKING.
The Clocking Function tells the router when to exactly send the bits through signaling over the cable.
When we connect the DCE cable in the serial port, the router automatically senses it and supplies Clocking.
Leased Line provides a Layer 1 service which is the reason Leased Line doesn't provide standard Data Link Protocol which is a Layer 2 service.
On the next post we will explain to you the two most popular Data lank protocol which are

HDLC (High-Level Data Link Protocol)
PPP (Point-To-Point Protocol)

Static Routing Description

Two methods are used to creating entries in Routing Table which are as follows

• Static Routing

• Dynamic Routing

Static Routing: In Static Routing, the Routing Tables are manually define by the Administrator.
Dynamic Routing: In Dynamic Routing, Automatic exchange is done between the Routing Tables.
RIP is the most common example of  Dynamic Routing. 

                                                           Static Routing

Now I will tell how static routing is applied between two routers. Following are the steps you have to follow.
First, Go to the packet tracer. Now you need 2 Routers, 2 Switches and 2 pc's and connect them like I have told you in the previous post. Assign IP's to the PC and then proceed to the CLI of router.
While Configuring for Static Routing, following will be written in the command:

• Destination Network ID (1)
• Destination Subnet Mask (2)
• Directly connected next hop IP address (3)

(1) , (2) and (3) are id no's given to them so when I will be showing you the commands, It will be easier for you to identify them.

Commands used in Router

Static Routing command for router 1

                                  (1)           (2)           (3)
R1(config)# ip route 20.0.0.0  255.0.0.0  15.0.0.2 

To see static Routing details, Following is the command

R1#Sh ip route 

Result of the command

C  E0 10.0.0.0/8
C  S0 15.0.0.0/8
S  S0 20.0.0.0/8 via 15.0.0.2/8

Static Routing command for router 2

                                   (1)           (2)           (3)
R2(config)# ip route 20.0.0.0  255.0.0.0  15.0.0.2

To see static Routing, Following is the command

R2#Sh ip route
 

Result of the command

C  E0 20.0.0.0/8
C  S0 15.0.0.0/8
S  S0 10.0.0.0/8 via 15.0.0.1/8

In the next post, I will teach you how dynamic routing is applied.