Networking Basics

Hi All

Below are some networking basics

Sometime there are patch panels between firewall and switch patch panels are basically a box with lot of ports are are cheaper than switches suppose your office want 1000 connection we can have 5 patch panes with 200 each and then connect those 5 patch panes to switch ports . Like you telephone line splitter. one wire goes in and two wire come out

 

VPN ( Virtual Private network)

VPN works on client server architecture. Suppose you have ciso vpn client then you need to have a cisco vpn server to connect to.It uses tunneling protocol

So VPN uses tunneling and encryption inside that tunneling to keep data secure.Now suppose a hacker tries to access the tunnel it drops the tunnel and creates a new tunnel taking a different route .

so how does it comes to know someone is penetratring its tunnel. suppose the signal it receives form client is not steady or if there are package loses it treats this as intrusion and drops teh tunnel so if you are working on DSL line (phone line modem) and if the wiring is old then the packets might drop due to bad wiring and this might cause the vpn to drop so you wont be able to connect to office network

second is the network speed inside your office is 100Mbps that is 10MB but when you are connecting through outside you speed will depend on the connection speed fo your internet so it might drop to 535KB. so it will take long time to access network

TCP/IP and Subnet Masking 

TCP stand for transmission control protocol and IP stands for internet protocol there are two version of tcp/IP version 4 and version 6.You must have noticed this as IPV4 nad IPV6 when you do ipconfig

IP- internet protocol deals with IP addresses ,subnet masking and default gateways.Its a routable protocol it allows n/w to be divided into multiple subnetwork.If it was non routable then all computers will be able to communicate with all others.IP is layer 3 of OSI layer

Windowing

This is a important concept in IP consider packets are sent from computer a to computer b then for every package sent to B computer A receives acknowlegement .now packages are sent in a group called window suppose first window only one packet is sent and if it receives acknowledgment packets are increased.Suppose in middle package starts droppeing so it receives acknowledgment that 2 packets received and it has sent 1000 packets then it will again sent those 1000 packets 

Now this IPV4 concepts of windowing might be problematic for real time communication like skype 

DCHP 

Dynamic host control protocol - there are two ways a IP can be assigned to your system.Static IP and dynamic IP.If you look into your modem or wifi router you will see this two settings.Consider you want to play counter strike with your roomate what you do is just make your IP static and ask your roomate to connect to your ip. then you two are no LAN and not on internet. Usually there is a lease time for which your WLAN router will assign ip to your computer it can be one day ,  one week one year 

ipconfig/release will renew your ip



NAT -- Network address translation 

Now when the internet intially started everyone thought each one would require a unique IP like a phone number so every computer that you buy should be registered NAT solves this issue.Insider your home if you have 5 computers then each one will have unique ip but they might start like 192.168.1.1 ,192.168.1.2,192.168.1.3 and so on. But even i will have the same ip for my home pc. this is because inside your lan you can your reuse ip. But your internet line comming to your home will have a unique ip.This is tracable from outside world .Suppose you do any cyber crime you will be caught by this ip. as they know to which provider a set of IP are assigned and they will get the house address from the internet provider like reliance. 

Subnet Masking

when you do ipconfig you will get ip address , subnet masking and default gateway.So subnet masking tells us which part of your ip is your computer number 

like example 

IP address---192.168.1.10

Subnet mask -- 255.255.255.0 

where you know the last bit wil be your computer numbers (10) as last is 0 in subnet mask.You can have 255 computers in your subnetwork. Consider you did not have subnetwork all the computers connected to a router or a same physical switch would be able to communicate that is if you are in one building with 20 flats 5 for each floor may be each floor is subnetwork using a subnet masking otherwise everyone can hack into others system if ports are open.

VOIP 

Skype , Cisco phones that we use in office are VOIP.VOIP hardphones are like computers and have their own ip address through which they can be accessed for configuration.

To configure VOIP in office you need a VOIP server ( a normal pc on which VOIP service is installed ) windows server is loaded with this service.But you can also have a cisco VOIP server. you will also need a client a softphone or a hardphone.

All VOIP phones (hard or soft) use SIP protocols ( session initiation protocol) but CISCO uses a free protocol whereas Avaya and Skype have their own protocols so if you have a Avaya server you cant connect other hardphones.

Codec -- determines the amount of bandwidth allocated to your VOIP communication in gtalk its 4.5kbps.Higher the bandwidth better the quality. you can set VOIP on priority in your router

In VOIP phones the latency is 75ms to 100ms.In normal phones it 45ms.The way VOIP reduces cost for most enterprises

Consider there is a office in middle of india and you have suboffices across.then office in village will have VOIP server and to that VOIP server you will have phones lines connected apart from internet line so when you call the call will come from delhi on internet line then from the local VOIP server connect to village local exchange so that call is charged as local and there is saving in terms of phone bill.

Network Mapping

ICMP - Internet control messaging protocol.It will have SNMP protocol inside it.

SMB shares , SNMP ( Simple network management protocol)

SNMP gives info like all software updates on your machine, all updates, all hardware info like RAM.this is how your network admin know you have installed unlicenced software on your laptop.

you can disable this service from your machine.There are software for network mapping which work on SNMP that gives you all the information

some useful commands are 

Tracert -- this will give you the full path that is how your computer reaches facebook 

tracert www.facebook.com 

will give you all details like routers , exchangs on the way and all that.

Gateway is anything that connects you to outside world.Usually in this world its modem.