Resolving Network Connectivity Issues
1.0 Network Connectivity
OSI – Open Systems Interconnect created by the ISO (International Standards Organization) Developed in the 1980’s
There are seven layers:
7– Application – Where the user is, recognizable communication applications like HTTP or FTP
6 – Presentation – Translation layer, translated into machine language
5 – Session – Traffic cop, computers are talking to each other, making sure the communication is in place, keeps the session in place
4 – Transport – Information is put into packets that the network can handle, makes sure they are transferred undamaged, uses protocols to do this, like TCPIP, expects to receive acknowledgement from the network on whether the packets have been received undamaged. If the packet is damaged, it will send another packet.
3 – Network – Responsible for addressing, TCPIP protocol uses IP addresses, puts the addresses on the packet before it is sent to the intended recipient.
2 – Data Link – Physical Addressing in order to get delivered to the individual computer, media access control layer and the logical link control layer. The logical link control layer links back up to the network layer. The media access control layer links down to the physical layer and contains the MAC address. The MAC address defines every computer in the network based on what network address in burned into its NIC (Network Interface card). The data link layer connects down to the physical layer.
1 – Physical – Data going out to the wire in bits, very fast and produces the ones and zeros, the binary language that computers understand.
1.1 IP Addressing
The government came up with TCPIP so that even if 7/8 of the government was blown to bits, 1/8 of it would survive and be able to communicate. Developed in the late 70s and called the 7/8 rule. The government gave the project to the universities to develop. The graduate students made up all sorts of rules, called Request for Comment, RFCs. The graduate students didn’t want to offend its potential employers, and wanted the corporations to comment on their rules. At the time, they had about 4 billion addresses to go around. They divided the address up into Class A, Class B, Class C addresses. Most of the time now, we use classless addresses called inter-domain routing. Each computer within a subnet has a unique address and each subnet within a network has a unique address.
Windows installs TCIP/IP automatically, if it finds a network adapter.
Devices on IP networks are called hosts. An IP address contains two pieces of information: the network id and the host id for that computer. All devices on a network must have the same network id, but the computers have a unique host id.
A router moves network traffic to the appropriate network in a multiple network environment. The router acts as a middleman between the client and the public internet. An ISP assigns private IP addresses to your DHCP server, built into your router, and the addresses are assigned to your home network devices. When your home network devices make a request to the internet, the router communicates directly with the Internet and passes the information back to the home network device. The router protects your device from the external Internet threats by never letting the device communicate directly with the internet.
Start/Run/Cmd/IPCONFIG/all
This command will tell you if the address is coming from a DHCP server and if the DHCP server is available, DHCP Enabled. DHCP servers are often built into routers. DHCP servers can assign a subnet mask, default gateway, DNS and WINS configuration. WINS is normally used in older Windows computers.
This command gives you the DHCP server address, the primary Wins server address, and all about the specifics of the IP address. If your client is having trouble with the DHCP addressing, and you know you have a DHCP server available on the network and that it is working, you can renew the address.
DHCP servers lease their IP configuration for a period of time specified by the DHCP administrator and the IP addresses are renewed each time the computer is started or when half the lease time has expired, whichever comes first. If the computer is not started before the lease expires, or if the DHCP server is unavailable, the computer loses its TCP/IP configuration.
Ipconfig /renew allows you to renew the IP address from the command line.
You can only make manual configuration changes from DHCP servers.
To do this, Start/Control Panel/Network Connections/Click on the connection the client is trying to use by right clicking/then click properties.
On the General tab, you have the following:
· Client for Microsoft Networks (the software the client is using built into the operation system)
· TCPIP Protocol and at the top of the dialog box you have the NIC card. Click on the TCPIP protocol. You will see the TCPIP address is being obtained automatically. If you want to set a specific static address, click 'Use the following IP address', and put in whatever address you want to use:
o IP address (required)
o Subnet mask (required) tells the TCP/IP host how to interpret IP addresses. A 255 in the subnet mask defines what portion of the IP address is the network address. A 0 indicates thisis part of the host ID.
o Default gateway (required) is typically a router. If the destination host is on the same network, the source host will attempt to communicate directly with the destination host. If the destination host is on a different network, the source host will use its default gateway to communicate with the destination host. A misconfigured default gateway will prevent you from gaining acess to resources outside of your network, but, will not prevent you from connecting to your internal network.
· If you want a specific DNS server address, you put in the particular address (optional)
o Preferred DNS server
o Alternate DNS server
If the DHCP server is not available, you have APIPA (Automatic Private IP Addressing). You will get an address returned 169.254.1.1 – 169.254.255.254 in that range. APIPA assigns IP address and subnet mask only.
In Windows XP, we have alternate configuration and can set it so if the computer does not obtain an address from the DHCP server, it can find an alternate address. Click on the Alternate Configuration tab, located beside the General tab. This gives you a tool to use the computer on two different networks, so that if you move the computer to a different network, it will find the configuration automatically, so you don’t have to reconfigure.
· Automatic private IP address (APIPA)
· User configured –If the computer does not obtain an automatic address from the DHCP server, it will use the User Configured address. Put in address that works with your other network.
o IP address
o Subnet mask
o Default gateway
· Preferred DNS server
· Alternate DNS server
· Preferred WINS server
· Alternate WINS server
1.2 Name Resolution
Servers translate IP addresses into names. Computers only know MAC addresses. You get the packet into the area you want it to go by the logical address, but then a router or computer will determine its MAC address and deliver it to the computer.
You have to know what the NETBIOS name and the HOST name of the computer is that you are working with. That might be information you need when troubleshooting. The NETBIOS name and the DNS host name are usually the same for a Windows computer.
There are two quick ways to find the host name:
· Right click My computer/Properties/Computer Name. Example: if the computer name is home, that would be the host name, but if it is part of a domain and the domain is Microsoft, it would be home.microsoft.com.
· Start/Run/Cmd/Hostname/Press enter
To get the NETBIOS name:
· Start/Run/Cmd/nbtstat –n (that stands for netbios over tcpip statistics and the –n stands for name). There are multiple NETBIOS names for a computer. NETBIOS names are used for different resources that the computer can offer. This computer’s NetBIOS name is Home and it is part of a workgroup. The NetBIOS Local Name Table is displayed listing the NetBIOS names.
NetBIOS Local Name Table
Name Type Status
HOME <00> UNIQUE Registered
WORKGROUP <00> GROUP Registered
HOME <03> UNIQUE Registered
HOME <20> UNIQUE Registered
WORKGROUP <1e> GROUP Registered
The main thing you want to look at is the 00 in the first NetBIOS name. You want to make sure it is 00. It is called the sixteenth bit and you should look to see if the sixteenth bit is 00 and it is unique name.
For detailed instructions on How to Configure TCP/IP to use DNS in Windows XP:
1.3 Remote Connection Issues
Remote connection is when a computer connects to us from outside our network. You need both speed and security.
· Virtual Private Networking: The user dials into a local ISP with a local telephone number and that puts them onto the internet. The internet can then connect over to the company servers and they haven’t made a long distance call. This increases security because there are encryption technologies used within VPN. VPN is used to avoid having the long distance telephone call and also it is more secure. It doesn’t add additional bandwidth because you are limited by the speed of the modem and the computer. Newer technologies like cable modem and DSL allow us to use lines that otherwise would not have high enough bandwidth. This now gives us greater bandwidth. With the VPN and the cable modem or DSL, you have almost as fast a connection as if you were sitting right at your desk in the office.
You might want to share connections, ICS Internet Connection Sharing.
Wizards configure these connections in XP.
Network Connection/Create a new connection brings up the New Connection wizard. Click Next.
· Connect to the Internet
· Connect to the network at my workplace (using VPN). Click Next.
· Set up a home or small office
· Set up an advanced connection
Create the following connection:
· Dial-up connection. Next. Type Company Name. Next. Type Telephone number.
or
· VPN connection. Next. Type Company Name. Next.
Do not dial the initial connection
Automatically dial this initial connection. Select the public network name. Next. Type in the host name or IP address where you connect (get the info from your ISP or your network administrator).
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