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Home network DHCP issue RedHat/WinXP

Posted on 2005-04-14
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Last Modified: 2013-12-06
I have a small home network. My Windows XP PC is connected to a router which is running a DHCP server and is connected to a broadband router. The (normal) router also connects to a hub with a RedHat 9 laptop connected to it. The router's DHCP client table contains the hostname of the laptop and the IP, but when I try to ping the laptop's hostname from the PC the hostname cannot be resolved. Is this to do with the laptop not being directly connected to the router or is there some sort of other potential issue?
I can provide more details if required - not sure what's relevant or not at the moment.

--Rob
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Question by:boycy
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by:purplepomegranite
ID: 13780830
It will not be resolved if the DNS server the PC uses is not aware of the laptop.

What DNS server does your PC use?  This can be found by:

- Start... Run... type "cmd" (without speech marks!) then ok
- DOS box will appear.  At the command prompt type: ipconfig /all
- You network config including DNS will be displayed.
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by:boycy
ID: 13780905
DNS's are my broadband provider's. I have no problem resolving names of other computers on the network, just the one attached via the hub.
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by:rain79
ID: 13782855
1.) Did you configure your Red Hat box, with a firewall? If you did, it might be (read probably is) blocking PING Requests...
2.) The hub should not affect PING Request, if you are on the same Router, so I would rule that out. If your setup was on different routers, then I would say, yes, it is possible that you cannot access one, or the other.

Can your Red Hat box PING your WinXP System? Or the router. If it does, I would check for the firewall...

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by:purplepomegranite
ID: 13782912
If DNS are your broadband providers, this is the problem.  The Windows machines will use Microsoft browser ( aservice that can resolve names using NetBIOS or other ways) to resolve Windows names, but your Linux laptop won't be resolved this way.  Also, your ISP's DNS servers will have no record of it (for obvious reasons)

I suggest adding an entry for your laptop in each Windows machine hosts file (located in windows\system32\drivers\etc).  Details are given in the file itself.
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by:rain79
ID: 13782993
purplepomegranite is right. I should have read the question more carefully..

Actually, I was wondering, can you PING the actual IP Address of your linux box ? If you can, then what he said is right, just put the name in the hosts file on your C Drive.. This would allow you to use its hostname..
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by:boycy
ID: 13786280
I can ping the IP address no problems. I don't get why the OS would affect it - surely a hostname is a hostname. It's nothing to do with the ISP - the router uses NAT or something similar so the ISP only knows of the router, not the individual computers on the network. I know I could put the IP into the hosts file but I'd rather not do that as the IP is liable to changing and it would be a real pain to have to change the entry every time.
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by:purplepomegranite
ID: 13786397
Yes, but hostnames are provided by DNS.  Your local network's names must be stored somewhere.  Windows machines manage this among themselves using the browser service - Linux does not.

If your machines are using your ISP's DNS servers, your ISP will not have any information about your local network (as you say).  If you turned off your Windows browser service, you would have no internal network even though the internet would still work (due to DNS).  The only thing allowing your Windows network to work is this browser service.

The only alternative you have would be to install a DNS server on your network.
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by:purplepomegranite
ID: 13786425
Basically, the browser service is what is storing these hostnames.  It doesn't extend this service to Linux, and Linux doesn't talk to the service anyway.  A hostname is a hostname yes, but where does a computer get them from?
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by:boycy
ID: 13786557
My computer browser service is currently disabled so that can't be the reason. My router obviously knows the hostnames of all the computers on this network (as they're shown in the DHCP client table) therefore I assume this is providing some sort of simple name resolution for the network.
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by:rain79
ID: 13786672
I don't get why you say that your IP Address would change.. The IP Address of the Red Hat machine should not change regardless of the IP Address of the router. By creating a Hosts file, and putting the information about your IP Address, I don't see why the IP Address of the machines would change, unless they get the IP Address from DHCP, but then the Router is totally useless.

Your Intranet should be set up with Static IP Addresses for all the computers behind the firewall..

If not, then the suggestion to have your primary DNS to your Linux box would be another idea..
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by:boycy
ID: 13786789
The internal (192.x.x.x) IP address of the Linux box is liable to change due to other network changes, as it gets its IP via DHCP. I agree - static IP would be a good way of solving this, the only reason I've avoided that is that this laptop is used on a different network where DHCP is used, and I have no control over that so I keep it on DHCP to avoid changing the setup each time I move it between networks.
By moving primary DNS to the Linux box do you mean putting this on the DMZ?
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by:purplepomegranite
ID: 13788849
DHCP does not provide network resolution.  All DHCP is does is manage IP addresses.  A DHCP server is usually configured to update a DNS server when it assigns IP addresses, which is how computers can look up hostnames.  DHCP categorically DOES NOT provide hostname lookup.

Microsoft deserve credit in that they have made setting up networks easy.  There is a lot that goes on in the background on a Microsoft network for this to happen.

Details of the browser service: http://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/TechRef/5914153e-c125-4d54-b5ce-a473fde4a672.mspx

The first paragraph of that link sums it up.
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by:purplepomegranite
ID: 13788888
Incidentally, I don't know enough about Linux to give you specific details, but I believe Samba can be configured to interact in the way you need.
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by:boycy
ID: 13788958
I know DHCP doesn't provide name lookup, I was saying that the router's DHCP server provides the IPs of some of the machines on the network, and in the DHCP client table on the router the IPs are listed *with the names*. My point was that the router obviously does know about the names of its DHCP clients, and as my machine isn't running the computer browser service then there must be some sort of other method of name resolution available, either from my machine or the router.
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purplepomegranite earned 500 total points
ID: 13789002
The router knows the names of the clients, but it won't tell any other machines on the network unless it is also a DNS server.

I was hasty when I said the Windows network would stop if the computer browser service was stopped, I can find no supporting evidence for this.  Apologies for misleading you in this regard.  There are other Windows services that can provide name resolution, such as Network Location Awareness (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winsock/winsock/network_location_awareness_service_provider_nla__2.asp).

However, your problem is still as said - your Linux box doesn't interact with any of these MS services, so it's name isn't resolved.
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by:boycy
ID: 13789309
Thanks for your help :)

Rob
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