setup: home lan of 8-9 machines - 4 win7 2 winxp 3 linux/solaris internet => Cable (comcast) modem => Cisco RVS4000 (gigabit) firewall/router I hope not to be too general but it is sort of a general question, but does get right down to details too. I've used/maintained a Static IP based home lan for several yrs, and am considering going to what seems to be a popular setup of all DHCP for home lan. But here is the rub for me. So far, I've never seen hot to smoothly integrate DHCP into the network. When ever I've tried to set a couple of machines to using dhcp addresses, right away I loose connectivity to them from the rest of the lan. I mean they are internet connected and from those machines all the lan network is visible, but they are not visible to the rest of lan. Here is a more detailed example of what I mean: A common scene on my home lan might go like this: Working on machine, I may have need of SSH connect to remote on the lan. Of courese SSH needs an IP address to connect to. So to ssh to a DHCP addressed machine how do I get the IP address? What I actually do is to go to the console of that machine run a browser and connect to little cgi script on my lans HTTP server that tells the clients exact ip address gleaned from the HTTP environment. Now, armed with the actual IP address I go back to the first machine and make the ssh connection. I may connect to several lan machines via ssh during a work session, running a cmd shell on them to check on files, grab some or do what ever I need done. But connecting is now either a matter of temporarily editing the hosts file on mach1, or just using IP numeric addresses for the dhcp served machine. Either way its more work. If I try windows native smb networking, shares that once were able to be connected to, now refuse to connect by smb names (unless I've edited the hosts file) and even then make take a while to become available. What bugs me to now end is that I strongly suspect all that jinking around is probably NOT NECESSARY, if only I knew better to handle a dhcp setup. I guess I understand the basics of dhcp connection, god nows I've setup many of them at times, and they worked. But how is one to maintain handy connectablility within the lan, without some means of handily obtaining IP addresses of all computers and making changes automatically to whatever so that they all know where the others are? How do other people manage that? Sager laptop NP8760 i7 1.73 Ghz 8GB ram

It sounds based on your description that you really need name resolution within your network. For a SOHO of 10 systems, a DHCP solution is a still "nice to have" but not required. The purpose of DHCP is to dynamically allocate and manage your IP space. Again for 10 systems, I wouldnt necessarily setup a dedicated DHCP solution to do that. since you mentioned that you have a firewall/router appliance, you could simply use the DHCP services that come with those types of boxes if needed. You mentioned the use of HOSTS files. This is where a DNS solution would greatly benefit you. Rather than keeping track of 10 machines with 10 entries in each hosts file, you could use an internal DNS solution to centrally manage the name to IP mapping. You would then configure your internal hosts to point to the internal DNS server(s). Everything else you mentioned at the application layer is not dependent on DNS or DHCP. Visit: anITKB.com, an IT Knowledge Base.

"It sounds based on your description that you really need name resolution within your network. For a SOHO of 10 systems, a DHCP solution is a still "nice to have" but not required. The purpose of DHCP is to dynamically allocate and manage your IP space. Again for 10 systems, I wouldnt necessarily setup a dedicated DHCP solution to do that. since you mentioned that you have a firewall/router appliance, you could simply use the DHCP services that come with those types of boxes if needed." First, thanks for the input. Sorry if these questions are based from a deep ignorance. Well, the dedicated part was meant to be thru that router. I'm not sure what you mean by dedicated but I'm speaking of letting 2 machines receive dhcp served addresses from my router. Or possibly the whole network to receive dhcp addresses from the router. You talk of a DNS solution being of great benefit. Do your mean to setup a lan machine to be a A dedicated dns server running `bind' or something similar? I've done that, and it is no trivial thing, unless you are speaking of something simpler... can you explain. If a home lan is served dhcp from its home router, and there is no dedicated DNS server in the home lan, how do the individual machines learn each others IP? Or do they just remain unable to communicate? How are the IPs learned even with a DNS server. I mean what is the process that takes place? What kind of query can even get to a dhcp served clients address to begin with, when the IP is only known by the DHCP server and client? Does the DHCP client broadcast its address in some way? If so, how is that broadcast received? What finally happens that allows an IP to be learned by any other member of the lan? Sager laptop NP8760 i7 1.73 Ghz 8GB ram

The simple answer (because it really is that simple). Most home/small office router's DHCP function also works as a simple DNS device. By simple I mean it's usually not possible to add static addresses to its address table - it only knows about the addresses it's assigned via DHCP. In short, this means that the router is capable of resolving any addresses it has given out to clients. Static addresses it doesn't have a clue about, that's why you get the behavior you've observed. Your Windows machines (both XP and 7) and Linux shouldn't have any problems receiving DHCP from your router; Solaris on the other hand... It's been my experience (with Solaris 8 and 9 on SPARC machines) that Solaris expects DHCP to also provide the host name along with the address; this is something that most simple router DHCP's just cannot do. If you're running Solaris 10 on Intel then it might be different.

some additional comments... Well, the dedicated part was meant to be thru that router. I'm not sure what you mean by dedicated but I'm speaking of letting 2 machines receive dhcp served addresses from my router. Or possibly the whole network to receive dhcp addresses from the router. I meant dedicated DHCP servers. You can use the DHCP service off of the router if you need the most basic DHCP solution. A DHCP server running on Windows (or linux-I am not familiar with) will most definately provide a more sophisticated solution, while still being easy, well easy for someone with DHCP admin experience. You talk of a DNS solution being of great benefit. Do your mean to setup a lan machine to be a A dedicated dns server running `bind' or something similar? I've done that, and it is no trivial thing, unless you are speaking of something simpler... can you explain. Yes, I meant a DNS server such as Windows DNS or BIND. DNS is relatively simple as well, unless you are completely unfamiliar. Its hard to justify a full DNS server solution for 10 computers, but it will make internal name resolution alot easier. If a home lan is served dhcp from its home router, and there is no dedicated DNS server in the home lan, how do the individual machines learn each others IP? Or do they just remain unable to communicate? The individual machines never "learn" about each other's IP. A DNS server will have a zone which contains computer to IP mappings. A client will query a DNS server and ask what is the IP for computerX? The DNS server responds with the IP that it has in the zone. The router that you have can do DNS PROXY, not full DNS. There are no zones. It only forwards to your ISP and caches results. Therefore it cannot be used for internal name resolution. How are the IPs learned even with a DNS server. I mean what is the process that takes place? Depends. DNS is not a new concept. For standard DNS, a DNS admin will need to populate the zone with records (not a big deal for 10 computers). For enterprise systems, say a Windows Active Directory environment, DNS support "dynamic DNS" (so do the verions of BIND) so the clients can "self" register. What kind of query can even get to a dhcp served clients address to begin with, when the IP is only known by the DHCP server and client? To communicate with another host on your network, you need to have the IP, no way around that. If you dont have the IP handy, you leverage DNS so that you can query it for the information. Think about how you connect to google.com. You don't have the IP, but you leverage DNS. Client communication has nothing to do with DHCP. DHCP only manages the IP lease process. Does the DHCP client broadcast its address in some way? If so, how is that broadcast received? No, clients do not broadcast their Name/IP..well thats not exactly true, but I know what you are asking. Actually when computer A wants to talk to computer B, computer A sends out an ARP packet (layer 2) for an IP and waits for a response from the IP owner to get computerB's MAC address, then local delivery can occur. What finally happens that allows an IP to be learned by any other member of the lan? This doesnt really happen. Think of the US mail delivery system. We really dont learn each other's addresses. If we want to send a letter, just put the address on the envelope and the USPS does it's thing to route the envelope. Visit: anITKB.com, an IT Knowledge Base.

The simple answer (because it really is that simple). Most home/small office router's DHCP function also works as a simple DNS device. By simple I mean it's usually not possible to add static addresses to its address table - it only knows about the addresses it's assigned via DHCP. In short, this means that the router is capable of resolving any addresses it has given out to clients. Static addresses it doesn't have a clue about, that's why you get the behavior you've observed. Your Windows machines (both XP and 7) and Linux shouldn't have any problems receiving DHCP from your router; Solaris on the other hand... It's been my experience (with Solaris 8 and 9 on SPARC machines) that Solaris expects DHCP to also provide the host name along with the address; this is something that most simple router DHCP's just cannot do. If you're running Solaris 10 on Intel then it might be different. Good input... thanks. Can I guess from your comments then that if the whole lan was dhcp served from the home router that the `simple' DNS you mention would handle communitcations between them all? Can you say in detail how one mach on the lan would talk to another machine on the lan when the whole lan has been served dhcp derived addresses? I'm sitting at my console... I don't know what IP has been given to mach2 but I want to access it... how do I proceed.Sager laptop NP8760 i7 1.73 Ghz 8GB ram

Good question. [JM]'s already explained that quite well (and in a lot of detail) in his reply. All you need to know is the name of the computer, DNS does the rest as far as figuring out what its IP address is. You're sitting at your console, you type in PING MACH2, MACH2 has no real meaning to the network itself, but it goes to DNS and says "Tell me what the address to MACH2 is please." DNS responds with "The address is xxx.xxx.xxx.xxx... kthxby." So the result is: C:\Users\bobr>ping arika Pinging arika.edcodie.com [172.19.11.248] with 32 bytes of data: Reply from 172.19.11.248: bytes=32 time<1ms TTL=128 Reply from 172.19.11.248: bytes=32 time<1ms TTL=128 Reply from 172.19.11.248: bytes=32 time<1ms TTL=128 Reply from 172.19.11.248: bytes=32 time<1ms TTL=128 Ping statistics for 172.19.11.248: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 0ms, Maximum = 0ms, Average = 0ms C:\Users\bobr>

[...] snipping for brevity Harry asked: If a home lan is served dhcp from its home router, and there is no dedicated DNS server in the home lan, how do the individual machines learn each others IP? Or do they just remain unable to communicate? JM replied: The individual machines never "learn" about each other's IP. A DNS server will have a zone which contains computer to IP mappings. A client will query a DNS server and ask what is the IP for computerX? The DNS server responds with the IP that it has in the zone. The router that you have can do DNS PROXY, not full DNS. There are no zones. It only forwards to your ISP and caches results. Therefore it cannot be used for internal name resolution. But I already stipulated the situation where: The Entire lan is served dhcp address from home router. No dedicated DNS server exists on the lan. So I guess you are saying that without some kind of dns server on the lan then the various machines will not be able to communicate? To be very specific here. With a home lan served dhcp addresses from home router, those machines will NOT be able to communicate? Harry asked: How are the IPs learned even with a DNS server. I mean what is the process that takes place? JM replied: Depends. DNS is not a new concept. For standard DNS, a DNS admin will need to populate the zone with records (not a big deal for 10 computers). For enterprise systems, say a Windows Active Directory environment, DNS support "dynamic DNS" (so do the verions of BIND) so the clients can "self" register. OK, now we are getting down to it. This `self' registering you speak of, what does it consist of. I mean what does the dhcp client do to `self' register? Harry asked: What kind of query can even get to a dhcp served clients address to begin with, when the IP is only known by the DHCP server and client? JM replied: To communicate with another host on your network, you need to have the IP, no way around that. If you dont have the IP handy, you leverage DNS so that you can query it for the information. Think about how you connect to google.com. You don't have the IP, but you leverage DNS. Client communication has nothing to do with DHCP. DHCP only manages the IP lease process. Harry asked: Does the DHCP client broadcast its address in some way? If so, how is that broadcast received? JM replied: No, clients do not broadcast their Name/IP..well thats not exactly true, but I know what you are asking. Actually when computer A wants to talk to computer B, computer A sends out an ARP packet (layer 2) for an IP and waits for a response from the IP owner to get computerB's MAC address, then local delivery can occur. Sorry to be so dense, but I'm a bit confused here. You say machA sends and ARP packet for an IP [...] But if machA got the IP from machB, why does it need the MAC? How did machA know what IP to fish for? How does this communication by MAC work? Harry asked: What finally happens that allows an IP to be learned by any other member of the lan? JM replied: This doesnt really happen. Think of the US mail delivery system. We really dont learn each other's addresses. If we want to send a letter, just put the address on the envelope and the USPS does it's thing to route the envelope. Ok, now I'm really confused. On one hand you say: " We really dont learn each other's addresses." But then you say: "If we want to send a letter, just put the address on the envelope and the USPS does it's thing to route the envelope." So the address was learned at some point in order to be able to be put on an envelope.... so the writer knew, going in, the address to the other person. Sager laptop NP8760 i7 1.73 Ghz 8GB ram

So I guess you are saying that without some kind of dns server on the lan then the various machines will not be able to communicate? That's exactly what he's saying. DHCP and DNS go together like rum and Coke (tm). To be very specific here. With a home lan served dhcp addresses from home router, those machines will NOT be able to communicate? That's not quite what he's saying... Your router functions as a DNS device, but only for the addresses it gives out via DHCP. This `self' registering you speak of, what does it consist of. I mean what does the dhcp client do to `self' register? To put it simply, the client announces to DNS that it has a valid address for that zone. But... the DNS has to support dynamic updating and this is another thing that a simple router cannot do. Its DNS table can only be updated by its own DHCP function, not from an external source. Sorry to be so dense, but I'm a bit confused here. You say machA sends and ARP packet for an IP [...] But if machA got the IP from machB, why does it need the MAC? It doesn't need the MAC per se, that's all internal to the machine itself. What he's trying to say is that each IP address is associated with one MAC address. This is why you can run into trouble if you have two devices with the same MAC address on the same network (it's rare, but it happens.)

Bob...thanks for the responses. Harry, while this thread has been very organized thanks to all involved so far, I don't know which questions have been answered, which you understand, which you are still confused on, and which have not been answered at all. So, maybe we should take one question at a time and not go to the next until it has been discussed an answered. While your questions are excellent, the responses may be very technical and depend on some foundation knowledge on your part. For instance, when it comes to the "self" registration question/answer, it could take a chapter of information from a Windows DNS book to fully explain the process of dynamic registration. Each of your questions have been very deep in technical nature and will be difficult to explain with short responses all at once. Visit: anITKB.com, an IT Knowledge Base.

Bob...thanks for the responses. Harry, while this thread has been very organized thanks to all involved so far, I don't know which questions have been answered, which you understand, which you are still confused on, and which have not been answered at all. So, maybe we should take one question at a time and not go to the next until it has been discussed an answered. While your questions are excellent, the responses may be very technical and depend on some foundation knowledge on your part. For instance, when it comes to the "self" registration question/answer, it could take a chapter of information from a Windows DNS book to fully explain the process of dynamic registration. Each of your questions have been very deep in technical nature and will be difficult to explain with short responses all at once. Visit: anITKB.com , an IT Knowledge Base. OK. good idea... this comment comes in somewhat out of order on my view but lets back track a bit. My original angle was to find out if I should expect a home lan served DHCP from a home router to be able to communicate between the various machines easily. From various comments in the thread, particularly the `rum and coke' reference, I can take that yes, that should be possible. Thats one down. Several technical question have been asked by me since but really the thing I most want to find out is why I don't see that behavior. But I think I might have gotten that answered to, by extrapolating a bit from comments here and some from another forum. So let me lay out what I think might be my trouble and then I'll have to give up because I cannot redo the lan right now. I'm in the middle of a fairly big (by my amateur videographer eyes) video production and need to be able to move large files around with diddling around about it. So right no I'm letting my Static lan stand. So to lay out what I think may be the stumbling blocks. 1) I've set hosts files up in all lan computers, so naturally if I allow a machine to accept a dhcp serverd address I must either alter or remove the hosts file. I think just renaming it would do the trick because I don't really think it is needed in an all dhcp lan. But not having done so would throw a monkey wrench into things. 2) I learned about the DNS-client service for the first time, I'm not sure if was in this thread or one on a different forum but as I understand it the service only clears its cache every so often and maybe why I did not see DHCP served machines show up at first. In response to Bobs' closing line above about chapters on DNS: This thread has made me recall quite a lot that I have learned some years ago and really never used much and so forgot most of it... I do need to reread some of the classics about this, so point well taken. So wrapping things up, I have reading to do and , a few experiments to try and I'm thinking then I will either have much more concrete questions or be enjoying a trouble free dhcp lan. Very much thanks to all participants, sever responses have been really helpful and informative. Sager laptop NP8760 i7 1.73 Ghz 8GB ram

I would agree with your recommendation and stick to a "static" IP based configuration. For ten computers, DHCP is not that critical. Just keep a good spreadsheet handy of machine names and IPs. As far as the HOSTS file, even for ten machines its a little painful, but since your IPs will not change, its a "set-it-and-forget" deal, until you add more computers to the LAN. Finally with DNS on your router, that really a DNS proxy service not meant for INTRANET (your LAN) name resolution but for INTERNET name resolution. You probably have the need for an internal DNS solution, something to keep on the radar. Ok, post any additional questions any time...For Bob and myself, any response will show up in our "My Threads" link no matter how long time passes. There are alot of other very experienced people that follow these threads so don't hesistate to post. Your likely to get more people to provide feedback when you ask direct, to the point questions. Visit: anITKB.com, an IT Knowledge Base.

[...] Finally with DNS on your router, that really a DNS proxy service not meant for INTRANET (your LAN) name resolution but for INTERNET name resolution. You probably have the need for an internal DNS solution, something to keep on the radar. Ok, post any additional questions any time...For Bob and myself, any response will show up in our "My Threads" link no matter how long time passes Thanks for your kind offer in the second paragraph above. I'm confused all over again by the first statement though. I understood from some of the comments that with an all dhcp lan the dns aspect is handled for the INTRANET. And I understood you to say in a previous post that they went together like "Rum and Coke" That is, that lan machines will be able to communicate by some lesser form of DNS that goes along with the DHCP service But you seem to be saying above it is only for INTERNET resolution. But maybe by `DNS' and `proxy' in this message you mean yet another lessor form of DNS in some other aspect of the router than is involved with dhcp service?Sager laptop NP8760 i7 1.73 Ghz 8GB ram

Technically [JM] is correct, the router is really a DNS proxy meant to forward DNS requests to the servers defined by the WAN connection. What happens on the intranet (LAN) side is that when the router receives a request for name resolution it queries its DHCP table to see if that address was one that it gave out. If it wasn't, it forwards the request to the WAN side for resolution by the DNS servers defined there. If it was, it returns the address of the machine that has that name in its DHCP table. So although it's not a true DNS device the end result is the same.

As my Linux box is a web server, I use my Linksys box as a router and it is aware of the primary domain. contract-developer.tk So the Acer machine which runs Linux becomes acer.contract-developer.tk and the Raidmax box is windows-7pc.contract-developers.tk And each of my virtual machines all have their own sub-domains as well. The router makes it easy to build a forest of machines. My MVP is for the Windows Desktop Experience, i.e. Windows XP, Vista and Windows 7 IT I am best with C++ and I am learning C# using Visual Studio 2010 Developer | Windows IT | Chess | Economics | Hardcore Games | Vegan Advocate | PC Reviews

Most routers will allow you to specify a domain name and then they will assign that to the machine as well via DHCP when it assigns an address. The domain name is usually optional and has to be manually entered by the user; it's a rare home router that will pick up a domain name automatically from a server, and at that, the router usually isn't serving DHCP, rather a regular DHCP server (such as Windows 2003, Windows 2008 or Linux) will be issuing addresses and probably acting as a DNS server as well.

I have DNS on the Linux box running and it takes care of all the needs. My MVP is for the Windows Desktop Experience, i.e. Windows XP, Vista and Windows 7 IT I am best with C++ and I am learning C# using Visual Studio 2010 Developer | Windows IT | Chess | Economics | Hardcore Games | Vegan Advocate | PC Reviews

Sure, and it's set to allow dynamic updates from the clients, right? And the clients get their DHCP info from the router? This isn't all that unusual. There's no reason that DNS and DHCP functions have to be on the same machine. In a Windows domain environment, where DNS and DHCP are both handled by Windows servers the DHCP service will automatically create the host records in the correct zone when it assigns an address. Otherwise, the client can be set to update the DNS zone when it receives an address from the DHCP server, although the DNS service has to be able to accept dynamic updates for this to work. Applying this back to the OP's question, he'd have to set up a separate DNS server (which is what [JM] suggested) and not rely on the router to resolve names (which was his original question - can a router serving DHCP do this?)

DHCP and DNS used to be separate machines eons ago, but today even a lowly old Celeron can manage a lot of services. The Broadcom processor on my LInksys box is even adequate. It can do DNS and DHCP which is what I use it for. My MVP is for the Windows Desktop Experience, i.e. Windows XP, Vista and Windows 7 IT I am best with C++ and I am learning C# using Visual Studio 2010 Developer | Windows IT | Chess | Economics | Hardcore Games | Vegan Advocate | PC Reviews

@Vegan--We are trying not to confuse the original poster. Yes, a linux box can be used. If you want to provide some additional help, you'll need to go back and read his posting in detail. I beleive that Bob and myself are on the same page here. Intranet DNS services where recommended since he has a LAN with only static IPs. An internal DNS solution would be of big help here, Windows or Linux. Visit: anITKB.com, an IT Knowledge Base.