8/27/05 Routers, switches, and hubs, oh my!

Hello Gary

The question I have not been able to answer is why do I need ip addresses on my network if the switch uses MAC addresses and not IP addresses.

What is the relationship between the two and what is their respective functions on the network. Also, where does the computer name, workgroup name and the lookup file come into play?

Thanks
Tom Rider

IP addresses identify a network (group of devices such as computers, routers, networkable printers, etc.) and also the individual computer (or other device) on that network. Routers use the IP address to transfer data from a computer on one network to another computer or server on a different network. Every time you go to www.somewebsite.com, your digital conversation is being handled by routers across the internet, and they use the IP addresses to make the connection.

MAC (Media Access Control) addresses are used by switches to direct traffic among your devices on your local network. They are simply unique "burned-in" or "hard-wired" identifiers on network interface cards (NIC) found in computers with an ethernet port where you plug into a network. Unlike IP addresses, you generally can't change MAC addresses. There's really no maintenance for you to do regarding MAC addresses. Switches automatically learn the MAC addresses of your computers by inspecting the data packets, and maintains a table of MAC addresses and what physical port a computer is connected to so that the switch can direct each data packet of traffic to just the correct destination port. This table is kept in memory, so once the power is shut down it all goes away; but the switch quickly learns to map out the ports that the computers are connected to and their MAC addresses when it is powered up again.

So the bottom line is that IP addresses are inherently used by computers to communicate with other computers that may or may not be on the same network. MAC addresses are used at a lower level on the local network for directing data communications. Even if you have an isolated network with no outside internet access, you would still use IP addresses because the operating systems follow a set of communication standards known as the OSI (Open Systems Interconnection) model. This 7-layer conceptual model describes how data is transferred all the way from the low level at the NIC, all the way to the upper level within the application. IP addressing is in the middle area. NICs, cables, hubs, switches, and routers are the hardware components that implement parts of the OSI model, and of course they all work together to do their own little part of the data transfer task. If you are interested in further detail, just search on "OSI model" and you will find volumes of good tutorials.

The computer name makes it easy for humans to access other computers on the network. If you are on a Windows-based computer, you may have used the Start>Run command to access a computer like \\TheServer\TheShare. You could have also accessed the same folder by using the form \\TheIPAddress\TheShare. Most folks find it easier to remember the computer name than the IP addresses.

Workgroup names are just another hierarchy in grouping computers into a network. You typically join a computer to a particular workgroup name that you have created, or if in a larger environment you may join the computer to a "domain" which just means that there is a special server on that network acting as a domain controller.

The lookup file you are probably referring to is the host file which is just a text mapping of IP address and computer "host" name. This file is for DNS (domain name service) host names. Another file, lmhosts, does the same thing for smaller networks using workgroups, but maps IP addresses with computer "LAN Manager" names. So what you are interested in is how name resolution works. Normally you don't need to worry with either the hosts or the lmhosts files because they require manual maintenance, but our modern systems now rely more on various dynamic memory tables. Plus, if your file has an incorrect mapping, you will be blocked from communications with that computer.

I threw in a little technical terminology Tom, but hey, this is a technical subject. If you have trouble with some of the terms, try looking it up at http://www.webopedia.com, http://www.computeruser.com/resources/dictionary, or any other of the wonderful web resources.

Tom, there are many different networking protocols. A protocol is a set of rules by which two objects (for example, computers) communicate. In this forum, we have discussed a protocol called Ethernet, which is probably the most widely used protocol today. Unfortuately, the Ethernet protocol is very limited. Electrically, it can only travel over short distances. Even with the recent Ethernet over fiber optical cable, we still are limited in range. Other protocols are needed to send data over long distances. Ethernet only knows how to communicate to other devices connected to the same switch or to other switches connected to that switch directly. It is a little complicated but, most swiches are very limited in the number of computers connected to them. Many of us have four-port switches, there are 8-port, 16-port, 32-port, 48, and so on. However, as we add more ports, we lose a bit of efficiency and performance and we can get a condition called ''collisions'' because the computers on the network try to avoid each other's data conversations but can't always. When a collision happens, the data packet must be repeated making the overall speed of the network much slower. Therefore, ethernet devices can only be connected to each other by hubs and switches in relatively small numbers. These networks are referred to as Local Area Networks (LANs) because of the distance limits as well as the limited number of practical connections.

To handle large numbers of computers or to go over large distances, we need to be able to connect the LANs together over a larger network that can handle the traffic. These are called ''Wide Area Networks'' or WANs. By connectinting networks together, we can have millions of computers all able to communicate together. This is the concept of the Internet.

Ethernet only knows about addresses of network interface cards (NICs) connected by hubs and/or switches directly. The hubs and switches do not know about computers that are across a WAN or across the internet. That is why we have another protocol called TCP/IP. TCP/IP is a ''routable'' protocol. That is, routers (mentioned earlier in the thread) know about the TCP/IP addresses and can search for networks around the world or, simply, in your home. They do this by knowing what other routers they connect to and asking them for help in locating a particular network.

The reason we use IP addresses is that routers can determine a location of another network by using these addresses but MAC addresses do not indicate any information about a network, only devices on a network. Therefore, most software we use is developed for use with TCP/IP and very little software, if any, is developed to use a MAC address. To use the postal example given, MAC addresses are much like the street address without a city, state or zip code. If you give a letter to your local carrier that just had an address of ''123 Main St.'' on the envelope, he may be able to deliver it if the address is in your town (but he probably won't unless you are very friendly with him). That street address is very much like a MAC address. If you wanted to send this envelope to an adress in another state or country, you'll need a different addressing concept that includes a city, state, postal code and country. This is similar to TCP/IP.

There are other protocols out there that do not use TCP/IP. An older protocol called IPX was developed that, simply, added a network number and a port number to a MAC address to be able to route messages between networks. The TCP/IP protocol is a better standard for communication and that protocol was used in designing the Internet.

So, in order to communicate between computers, even between computers in your home, most software is written to use TCP/IP. The MAC address is only used in the LAN (for example, in your home) to operate at the lower levels of the TCP/IP operating system since it is best geared for the electrical connections between computers and not routing information between networks. Therefore, TCP/IP needs MAC addresses as these are the addresses of the network interfaces on your network, but they use IP addresses to talk to other networks and it needs the ability to translate addresses back and forth locally.

I hope this helps.

mccaffsj and Hforman are right. You cannot do without assigning IP addresses because thats how networks work.

I think what you're trying to ask is "if i have two computers, and i plug them into a switch, and i do not have an internet connection, why should i need ip addresses?".
Well, simply put, what you would be creating is not a network. For a set of computers to be part of a network, they must have the same form of IP address. This is how the OSI model (the basic networking model) was created to work so its a standard that must be adhered to at all times. Windows will refuse to acknowledge the presence of a network if both computers have different ip addresses (or no ip addresses). If you try to send a message from one computer to the other, it is irrelevant that the switch can understand mac addresses, because windows will believe this other computer does not exist and that you have lost your mind. It will not even attempt to send the message to the other computer and you will be given an error.

So basically its not that you need the ip address for the switch to work. You need the ip address to meet standard protocol so that windows will actually recognize the presence of the network, and allow you to even attempt to communicate. Its a rule that you must follow.

Gary.

each machine the same IP address?

Change the last group of numbers of the IP address for each different computer on you network. doesn't matter what you change them to as long as they are all different

please when assigning IP addresses save yourself alot of trouble and do not assign #001, #128, #254 and #255.
IP addresses are in the form of 4 groups of numbers separated by dots. each numer is from 0 to 255 so possible numbers for IP are....
0.0.0.0 thru 255.255.255.255
on your LAN typical assignments are 10.0.0.x
with x being a number 0 to 255. again avoid the above numbers.
or 192.168.0.x same note as above
these are typical "Private" address ranges the second last number can be anything 0-255 but needs to be the same for a LAN to work
e.g. 192.168.0.1 cannot communicate directly with192.168.1.1 but 192.168.1.1 can communicate directly with 192.168.1.2 the second last number is the LAN number.
and the last number is the computer itselfs numbe in the network but they do not need to be consecutive numbers. 192.168.1.1 192.168.1.22 192.168.1.123 whatever. I like to use LAN computer numbers that are ODD consecutive numbers in groups of 10-30 i like to start above number 10 but below 240 as mentioned below. pretty much this is upto you if you choose to manually assign numbers.
by convention number above 240 are usually reserved for network devices like switches and routers ect. so avoid these also for computers.
ron

... you might as well explain how the network mask works.

When your computer (or a router) tries to interpret an IP address, it doesn't actually see (for example) 192.168.0.1, but instead it will see that in binary form:
11000000.10101000.00000000.00000001

The reason addresses staring with 192 or 128 are considered special "private network" addresses is because in binary form they start with a 1 or a series of 1's.

So what's this network mask? Well, basically it forms a mask over the IP address, telling the computer or the router which part is going to be the same for all the computers within the same network.
This is why for most small networks, the network mask is 255.255.255.0 - because 255 in binary is 11111111, and the computer simply ignores those parts masked by a 1 (or alternately, the router only looks at the part being masked, and ignores the more detailed information when deciding which network to send a packet to.

For a small network, you will generally use 255.255.255.0 as a mask, and thus tell the computer to only consider the last number as a unique identifier within the network.

This means that for larger networks, the network mask might be only 255.255.0.0, because otherwise you would not be able to have more than 255 computers on any subnet.
Subnet masks can even take the form of 11111111.11111111.11111111.11110000., which would translate as 255.255.255.240, and basically reduce your subnet to 15 usable addresses (using only the last 4 bits).

For a home network though, it's best to stick to a much simpler subnet mask of 255.255.255.0, and an address in one of the standard private ranges mentioned by other posters (i.e. 10.x.x.x, 128.x.x.x, 192.168.x.x, ...)

my understanding is a network consists, in the strictest definition, as any two or more computers connected together for the purpose of sharing resources. these would be files OR printers OR drives ect.
to communicate they must have a common communication "protocol" or as you said communication RULES. since USB and parrallel ports can be used to form a network, your statement about the required TCP/IP protocol is not exactly true since neither USB nor Parrallel nor serial use it.
secondly, the question should be answered....
"if i am not connecting to the internet and my LAN is 2-3 computers and i use a switch to connect them..why do i need to assign IP addresses?"
YOU DON"T ! PLAIN AND SIMPLE...unfortunately, microsoft with Windows XP has decided TCP/IP is turned on and can't be turned off.so IP addresses WILL be assigned, possibly dynamically, automatically.
even if you use a router connected to a switch that connects to your LAN, you WILL BE ABLE to surf the internet because the router will give it's IP address out attached to all of your LAN communications and the switch will route the returned messages to the correct PC on your LAN.
If you use Win XP set your router to act as a DHCP Server and have it give out IP (Internet Protocol btw) addresses to your LAN computers if you set your LAN computers to TCP/IP automatic configuration.
hope this helps
ron

You are correct in the definition of "network" however you have taken this discussion beyond the scope of the original question. The question was posed by a home user what are hubs, switches, routers, gateways, etc.
The home user's confusion is understandable considering the information sources that they must rely upon, ie. sales people at local computer store and inaccurate information on posts like this, most times will be incomplete or completely inaccurate.
Networked devices do require a defined protocol regardless of connection type to allow communication. Also required are unique addresses. In the context of the initial question TCP/IP is an appropriate protocol as this is the language of the internet. It was chosen due to it's cross platform capabilities (MAC, Linux, etc). If one wanted to configure a network using a different protocol, all Windows OS's can be configured as such....TCP/IP can be disabled. If you have a SWITCH connecting several computers IP addresses DO IN FACT NEED TO BE ASSIGNED SOMEHOW. Typically a router would allocate IP addresses through the normal discovery process however a switch is only a physical connection between the computers. A computer acting as a proxy server or a router needs to hand out IP addresses or IP addresses need to be manually assigned!

Gary, Your explanation of the components was spot on. However, your recommendations at the end were off.
Most ?Broadband Router?s? on the market today have a built-in switch with 3 to 4 ports. This allows you to connect your network directly to the router and avoid buying a hub or switch in addition to the router.
The gateway-router is the backbone of the small network and takes care of most of the technical details in making a network work. All the computers on the network must have unique IP addresses, much like every house on a street has it?s own number. This address can be assigned manually (but must be within certain allowed addresses) or it can be assigned automatically by your router (this gets more complicated if you have a server installed). The MAC number is more like the plat number that the city has in it?s records about your house, only the true wonks will ever care what it is and you don?t usually need to know it even exists.
You asked about firewalls. Every one of your computers should have a software firewall installed, this can be the free one that is included with WindowsXP service pack 2 or one that you pay for such as Norton Internet Security, eTrust firewall, Zone Alarm, or one of the many others. You get what you pay for. The firewall prevents others from entering your system and most also prevent your system from unexpectedly communicating with others. It is a hassle to go through the process of training the firewall to allow your programs to access the internet, but over a few days most of the ?warnings? stop and you can get on with enjoying your computer. Also your gateway-router will act as a simple but effective firewall called a Network-Address-Translation firewall, simply put this blocks messages from outside your network that are not specifically requested by systems inside your network.
For a typical DSL sharing system you will connect a gateway-router (?Broadband Router?) to the DSL modem and your computers to the router. You an use either wires or, if you have bought a model with wireless, connect wireless. You should follow the user?s manual directions and change the router?s username and password from the default. Have fun!

As stated, SOHO (Small Office, Home Office) networking can be done with one unit nowdays. DLink, Linksys, Belkin and other companies have really done a good job over the past few years to make home networking simple and affordable. If you go wired, a ethernet router with built-in 4 port switch runs around $50. If you go wireless, a ethernet router with built-in 4 port switch runs around $100 (your more basic models run under $100, while more advanced models run slighty over $100).

Using dial-up brings up a good point. I used to use a hub to do internet connection sharing with Windows 98 SE, but since then I haven't touched it. If a ethernet router can handle internet connection sharing, I would still suggest buying the ethernet router over a hub so you have broadband upgrade options in the future. Broadband and dial-up are so close in price today that unless you could only afford free - $10 a month for dial-up, spending $20 - $30 a month for broadband is the way to go.

Last point, if you go wireless, make sure to read the manual and if the router setup has a wizard, make sure to go through that as well. That helps with some of the basic setup. The important thing is to setup a WEP/WPA key that basically secures your system so that only you have access to it. If you have trouble setting up a wireless secure network, your local computer company should be helpful in answering any questions, or other people on these forums.

i agree. many routers come with built in switches nowadays. i was just blindly following my previous theoretic knowledge so my setup was a little outdated.
its good you raised that point.
gary.

Ericwolf, I bought a Linksys wireless router for my Compaq laptop to link with my hard wired desktop. Each time I want to use the laptop, I must go through several steps to activate the connection. I have comcast highspeed service to the HP desktop. Here are the steps I must go through each time I want access to the internet:
1. Per the Lynksys help desk, I must run services.mcs
2. In the Services window, I scroll sown to Wireless Zero Configuration and click on it.
3. I click the Start service icon.
4. I then right click on the Wireless Network Connection icon in the lower right corner of the screen.
5. I click on View Available Networks title.
6. In the Wireless Network window, I click on the Change Advanced Settings icon.
7. In the Wireless Connection window, I click on the Wireless Networks tab.
8. In that window, I need to put a check mark in the box next to "Use Windows to configure my wireless network settings".
9. Now in the Preferred networks box, my Linksys connection is there, where prior to the check mark, it wasn't.
10. I click OK and I get an info bubble advising me that the "Wireless network Connection 3 is now connected".
Now, most times, it seems to cycle between being connected and not connected, back and forth several times. It seems to stay connected after I access the internet for the first time.

Linksys help desk advises that I must go through this each time I want to connect to the internet. Is this true? It seems like a lot to go through each time I turn on my laptop.


Now after booting up, my laptop advised me that (message from Norton) Windows firewall in one or more of the connections. Do I want to turn it off. Lynksys advised me toturn it off. Then a bubble advised that one or more wireless networks are available.

Hi
The same thing used to happen to me, although some times it connected without going through all that process.
I have learned from friend it because the router some times will not give an IP address to the wireless USB device.
Just pray, when you turn your laptop on, sometimes it helps.

Are you still using the system or did you change it out or did you just give up?

Ghost, It sounds like your firewall is preventing you from using the wireless connecton.
If you get a message that wireless connections are available AND you can connect to the Linksys when the firewall is turned off, then you will have to go through the firewall settings to make sure that the wireless connection is not being blocked. Let us know which firewall program you are using if you have trouble.

On the laptop, I'm using Norton. On the desktop, I'm using the WinXP provided firewall.

what is the use of MAC address? Why we need MAC address while we already have IP address?

I read on one of the Q&A's that you gave out. I must say that you explained the the answer very understandable, Just wanted to let you know that. Great job and one of these days I may have a Qs for you too.

Vernon

thank you

I have a follow-up question to Andrew's queries about routers, switches and hubs. I'm also trying to connect three computers, but with DSL service.

My problem is that my dsl is not stand-alone, but a pci card. Since purchasing a laptop, I wanted to add wireless. I bought a wireless g router and card for the laptop. Normally this would be easy to add, diseminating the dsl signal to all and file/printer-sharing from the device, but there is no output on the dsl pci itself. So the first computer already has its service by the time the dsl signals exit via a nic. This was fine on my two computer network, using a crosswire cable but ...

Not now. I've tried ethernet cable to both the WAN and LAN inputs but can't get all three computers to see each other or share files, to say nothing of internet connection. The best I've managed is through the WAN - I can get two computers to see each other and all three to share the internet. Through the LAN input with DHCP turned off I can get the two wired computers to see each other (only one will share files) and that's it. The laptop is in the wilderness.

I've been told by the router manufacturer that I can do this, but it's an XP issue so they won't guide me through it. Others have expressed mixed opinions. I'm wondering if another crosswire cable instead of the short straight throughput one will solve the problem? What are your thoughts?

I'm doing this mostly as memory as this is NOT how I have mine setup. I don't like using my PC as the gateway for my home network. But having said that...

First, I'm assuming the DSL PC also has a NIC. Run the MS Ineternet connection sharing wizard. There's a how-to here: http://support.microsoft.com/kb/306126/

This will set your computer to have a static IP address of 192.168.0.1 (if you take the defaults) on the NIC, to use DHCP on the DSL card, and to act as a DHCP server. This is where the first conflict comes into play. All the home router/gateways I've set up like to default to 192.168.0.1 also. So your choice here is to use a different IP for the computer (change the last number to 2) or to log onto your router first and change it's IP address.

Turn off the DHCP server function and WAN on your router, otherwise your client computers will end up getting their IP info from two different sources. Next plug all the hard-wired computers into the LAN ports.

On all your PCs you now have to set up the clients. The How-To listed above show how to do that also. Turn on the wireless devices and configure them.

This should do it. Except to insure you're running the firewall on the gateway computer.

I too have a similar network setup to the one described.

My internet access is through Starband Satelite and they require software to format the data messages for transmission over the sat.

So I need a PC to run that software.

My Inet "Server" PC has two NICs. One to the Satelite modem and one to my network. This is all this machine does. It has the firewall also, eTrust Firewall is what I use.

I use ICS on the server machine to share the internet connection. XP automatically sets up the internet NIC with DHCP so it gets its IP from the internet gateway at the provider. The LAN NIC is then setup with 192.168.0.1 and serves as the access point for the lan to get to the internet through this gateway machine. The LAN NIC is attached to a Switch, which connects to four other computers and another switch. The second switch is also connected to two other comuters and a wireless router. The wireless router drives two laptops in the house. Since it is not really doing router duties, I have it set to be a simple switch/access point.

All LAN attached PCs are set to gateway through 192.168.0.1 and also DNS through 192.168.0.1. This provides Inet acess to everyone in the house.

-Sat modem
---Inet Computer, XP Pro
-----Switch1
-------Comp1, XP Pro/Suse 9.1 Pro
-------Comp2, XP Pro/Suse 9.3 Pro
-------Comp3, Suse 9.3 Pro
-------Comp4, XP Home/Suse 9.3 Pro
-------Switch2
---------Comp5, XP Home/Suse 9.3 Pro
---------Laptop1 through NIC, XP Pro/Suse 9.3 Pro
---------Wireless Router
-----------Laptop1 through WLAN
-----------Laptop2, XP Home

Just goes to show you what a little insanity can do to your network!!

Chris

Why get a hub/switch AND a router? You mention cost as being a factor so why not recommend a 4 port router like Linsys or Netgear? I know 4 port wireless Linksys routers go for $60 or so at Sam's Club and Wal-Mart. Cheap, easy, built in firewall, and only one device to worry about. (and by ISP "router" I assume you mean the cable or DSL modem. I've never had one of those that came with a firewall or any user-configurable functions at all)

is the simplest method. And combination Wired/Wireless G-Routers can be had for $20 with rebates now! These are great IF you are dealing with a straight DSL/Cable modem connection to the internet, and they are usually almost plug and play!

However there certainly ARE DSL "Modem/Router/firewall" combinations provided by our local Sprint provider that have only a single port for a pc connection. I would guess these MIGHT be able to use a simple hub or switch to share the connection with many computers but the configuration would be more complicated.

you are right. it is a perfectly good option and probably the smarter choice for a home network. i tend to think in terms of giant networks where such a setup would be inadequate but for a home network it is a good idea, and hassle free.

Andrew! Your answer was excellent. I like the patience U have taken to explain to the user. For me, it like a refesher/review session. Thank U!

er..did u mean gary?