Drew Wutka
DWUTKA at marlow.com
Tue Jan 28 17:01:07 CST 2003
Sounds like you need a Jack of all trades! <VBEG> I'll be glad to help out. I'm sending this to you and the list, since I will put some general info in here which can only help anyone with understanding how a network works. If you have more specific questions John, feel free to email me offline. (use dwutka at marlow.com or drew at wolfwares.com). If anyone else reading this doesn't want to learn a bit, just stop reading. Okay, to begin with, TCP/IP is Transfer Control Protocol/Internet Protocol, which is the protocol used to communicate through the internet. TCP/IP can also be used within a LAN. So how does it work? Well, to make a network protocol work, the first thing you need to do is create a method of identifying each machine on the network. With TCP/IP, that 'id' is the IP Address. Your IP address is made up of 4 bytes, or quads. (192.168.0.1, each of those numbers is going to be within a byte's range, 0 to 255). Now, with IP Addresses, Numbers get assigned from the left to the right. What that means is, an organization that requires a lot of addresses may get the entire range of 146.xxx.xxx.xxx, which is a ton of addresses (255^3), where as a smaller company may get 156.134.21.xxx which is only 255 addresses, and of course and individual user will usually only get 1 IP Address. There are several 'reserved' addresses, which are predesignated for various functions. For internal networks, or LANs, 10.10.xxx.xxx and 192.168.xxx.xxx are set aside. What does that mean. That means that there can be many computers turned on with the IP address of 192.168.0.2, but none of them would be allowed to access the internet directly, since that is a LAN specified IP address and that would place multiple machines with the same 'id' in direct contact (which is not allowed to happen, otherwise TCP/IP would not work) John, I am sure you knew that much, just providing a little background. Now there are two other 'properties' that are in direct relation to the IP address. The first is the subnet mask. The subnet mask refers to the 'subnet' that a computer is on. 255.255.255.0 means that the subnet for 192.168.0.3 is all IP addresses with 192.168.0.xxx. The way to 'figure' a subnet, is to use bit comparison against the subnet mask. 255 is all bits turned on, so that number is an exact match. 0 is all bits off, so that entire quad is a variable. In between that, you have 254, which means the last bit is variable, etc. What makes the subnet mask important, is that when a computer needs to 'scan' it's surroundings, it uses the subnet mask to determine what addresses to talk to. (JC...important to remember this...) A good example of how this effects things is an issue I have seen with Windows 98 machines. Our subnet at work is 255.255.254.0, which means the internal IP addresses are 192.168.0.xxx and 192.168.1.xxx. The problem on the 98 machines is that sometimes we get a NIC that set's it's subnet to 255.255.0.0. That is roughly 65,000 addresses. With that many addresses to scan, network connections time out. So what makes this important, is that your subnet needs to be large enough to accomodate the numbe of computers it is going to support, and no larger, because a larger subnet takes longer to 'scan'. The next important item is the gateway, which is the Address of the router for a subnet. You must have a router 'in front' of every subnet. A router acts as a phone switch box between subnets. The gateway must be in the same subnet as the local IP address (unless you are setting up a router...that's a different story all together). A router 'knows' what is on either side of it, so it will either pass packets back into the subnet it covers, or send them off to another subnet, based upon the addressing. Now that you know the basics of TCP/IP, it's time for the 'support' processes, which is where you are running into problems JC. The first support item is DHCP. DHCP stands for Dynamic Host Configuration Protocol. When it comes to your TCP/IP settings mentioned above, there are two ways to set them. Manually enter the settings, which is refered to as a static IP, or getting them from a DHCP server. How does a DHCP server work? It's actually pretty simple. It has a 'cache' of addresses that it is allowed to 'hand out'. It also has a 'settings structure' that it gives to it's clients. That structure dictates the subnet, and gateway properties. It can also include items such as DNS and WINS settings (and more). So here's the trick, how do you get an IP address without having an IP Address to communicate with. What happens is your computer broadcasts a DHCP request. It's essentially 'protocolless'. It does this by using your machine's MAC address (which is the unique ID of your network card. IP Addresses are used because there is no rhyme or reason to a MAC address, so it would be a real pain to 'route' between subnets based on MAC Addresses, so TCP/IP overlays the MAC Address. Sort of like the difference between using a phone number versus genetic code. You can absolutely find the right person with genetic code, but when you find the first genome, you don't have a specific direction to head in, where as a phone number starts with an area code or country code, which automatically sends you to the right region.) This too is important, because a DHCP server can be setup with 'reservations' based on a MAC Address. What that means, is that when a request comes in to a DHCP server, from a client machine, the DHCP server looks at the MAC address, and if there is a reservation for that address, it hands out the assigned IP Address for the reservation. If it does not have a reservation, it hands out any 'available' address. This allows you to use a DHCP setup, while maintaining relatively 'static' IP addresses. The advantage to this, is that you can change these 'static' IPs from the server, instead of having to go to each machine. The last thing you would want to know about a DHCP server, is that the 'broadcast' message that a client machine sends out, is broadcast only within a subnet. In other words, all switches and hubs will pass the signal to all of their ports, but a router will not let it pass. Thus, you must have a DHCP server 'within' both your TCP/IP subnet, and physical subnet. It's also why many routers have DHCP capabilities. There is certainly a lot more, but that's all you need to know to fix your problem. You need to setup your DHCP server to hand out not only the right addresses, but the right information for those addresses (subnet and gateway). If I remember right JC, you talked about setting up a Windows 2000 server on your home network. Did you do that. If so, you can just drop using the DHCP in your router, and instead turn on the DHCP service on your server. Windows 2000's DHCP server is as easy to setup as choosing your wallpaper. Setting up a DHCP service within a router requires reading the manual, and learning to program your router. Each router is different. Some have handy 'web' interfaces (just try http://192.168.0.1), or whatever your gateway is. If your router will let you modify it's settings through the web, you just need to find the DHCP settings, and setup the IP Address Pool (which should include the 'settings' for that pool). Technically a router's DHCP is going to be a little faster then a servers, because it is a hard wired service, instead of a software service. But we are talking nanoseconds, and if your router is a pain to setup, those nanoseconds are worthless against an easy GUI option. Also, if you have a Windows 2000 Server machine running, you can setup your own WINS and DNS services. Having your own DNS server is EXTREMELY handy. For example....when my DSL is working, I just open my browser and type email in the address, and i am brought to our Outlook Web Access site. Intranet brings me to our Intranet site. This is done, by setting up my own DNS 'aliases'. Any who, if none of this helps, or you want some more specific help, either email me, or if you want to go the Windows 2000 Server route, give me a call. (Actually, if you email me with your #, I'll call you on my cell phone...weekend minutes are practically free) I can walk you through the settings step by step. (My DSL might be down (actually it will hopefully be up tomorrow), but my server is still running, so I have a running resource to compare settings with. (I set it all up myself...I'm actually running Active Directory, which I HIGHLY recommend, but it's not for the faint of heart! <VBG>). Drew -----Original Message----- From: John W. Colby To: AccessD Sent: 1/24/03 10:11 AM Subject: [AccessD] OT: network help Guys, I am having network troubles at my home office. Here's the situation. I have a small network running on a dlink DL-704 router. WWW connection through my cable, thus a cable modem. The router is the dhcp server. Internal addresses were 192.168.0.x with the router being 192.168.0.1. Understand I am not a network guy so I can spout this stuff but you should not mistakenly conclude that I understand it. The problems started when I tried to set up a Remote Access connection to a client system. I could get the virtual channel to run but couldn't get to the "server" on that system which was set (internally to THEIR network) to 192.168.0.10. The problem is that their network and mine were both using 192.168.0.xxx. The network guy that set everything up for the client asked me to change my system to 192.168.1.xxx which I did. Everything came to a crashing halt on my system, at least in terms of getting to the internet. In fact weird things would happen like... some chat clients worked (yahoo and aol), others didn't (msn). On closer investigation it seems that the default gateway is still set to 192.168.0.1. Since everything else is set to 192.168.1.xxx (including the router - 192.168.1.1) it appears that this default gateway number is causing havoc. We could not find where this number is assigned, IOW how to change it (default gateway) from 192.168.0.1 to 192.168.1.1. The "answer" was to go set the TCP/IP properties manually to "use the following address" instead of "Obtain an IP address automatically". Once I go in there and set the info manually, including the "default gateway", everything works. However this now means that I have to manually configure all of my computers since when they obtain automatically, they end up with the default gateway address of 192.168.0.1 which doesn't work. This is going to cause problems when I hook up my tivo box which I can't get at the settings to set manually. So... the question is, where the hell is this Default Gateway setting configured. It seems like it should be part of the router configuration but I simply cannot find that setting in the router's setup stuff anywhere. If anyone can help me with this, it would be much appreciated. We can email (offline) at jcolby at colbyconsulting.com or (preferably) use chat at jcolby at colbyconsulting.com for MSN, jcolby_c2db for yahoo, or jcolbyC2Db for AOL. TIA, John W. Colby Colby Consulting www.ColbyConsulting.com This list sponsored by Database Advisors Inc., a worldwide association of database developers. Visit http://www.DatabaseAdvisors.com, the database developers' list portal and support site.