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PC disconnects from network when IP automatically assigned by router/ISP

Posted on 2006-05-10
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Last Modified: 2008-02-01
Small business (printer) with peer to peer network with one Mac (OS 9.2) and one PC running Windows XP Home.  Up to now, internet access has been thru AOL dialup. Each computer and printer assigned a unique IP address (13.248.10.XXX).   DSL recently installed, static IP address range.  I set up a DSL router and connected the exissting 16 port switch via regular Ethernet patch cable.  After I set up the TCP/IP in the Mac to auto assign, it worked fine on both Internet and printing to all the printers.  However, when I set the Windows PC to automatically assign the IP address, I can get the Internet, but I lose connection to the Mac and all the printers, which just won't do.  I didn't set up this network in its original configuration, so that's about all I know about it.  Help!  Client is very anxious.  Too late to get help from DSL support, and I don't expect too much from them.  They're mostly concerned with the DSL to the job site, it seems.
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Question by:jimblunt
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bstrauss3 earned 1000 total points
ID: 16653727
Remember - all the devices will get new IP addresses.

Either in the new range, or possibly - if the DSL router is acting as a NAT device - in the 192.168.x.x range.

You'll need to update the pointers on the XP box to the new addresses!

-----Burton
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Expert Comment

by:b0lsc0tt
ID: 16653745
jimblunt,

Is the DSL router set to assign IP address (DHCP)?  It sounds like, but please confirm, that you have the Mac and PC set to automatically obtain the IP address.  What IP address is on the Mac and the PC?  What is the setting for gateway and subnet mask on each computer?  Those settings should be the same on each computer.

When you mentioned setting up the computer(s) to auto assign that may be having the computer act as DHCP server.  It is best to let the router do that and have each computer get (i.e. obtain) the IP from the router.  The IP's would be similar (e.g. 192.168.1.100 and 192.168.1.101).

Let us know what results you get and how this works.

b0lsc0tt
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Author Comment

by:jimblunt
ID: 16653983
These are the settings that I put into the router:

Static IP address:  11.111.11.1
Subnet mask:  11.111.1
Default gateway:  11.111.11
Primary DNS:  11.111.111
Secondary DNS:  11.111.11

Both Mac and PC are set to automatically assign the IP address.  I assume the router does that.
Before I set up the router and introduced DSL into the network, the PC IP address was 11.111.11, and the subnet mask was 255.255.255.0.
I won't have the PC and Mac IPs until I revisit the client site tomorrow.
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by:b0lsc0tt
b0lsc0tt earned 1000 total points
ID: 16654036
Thanks for the reply although the public information you posted is not needed for this problem.  I have posted to CS to ask them to edit it.

The PC ip that you posted is also a public ip and may be the problem or part of the problem with the local network.  Let me know what you get from the computers since that is the information that is important.  Make sure that they are not acting as DHCP servers but are obtaining the IP from the router.  The router's LAN ip should be the same address that appears on the computers as gateway.

Hopefully the information above and in my previous posts will help you solve the problem when you visit the client and look at the settings on the Mac and PC.  Otherwise post their information (e.g. ip address, gateway and subnet mask).  This should not be public but in the private range of ip's (i.e. 10.x.x.x, 192.168.x.x).
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Author Comment

by:jimblunt
ID: 16654698
Thanks for the comments, b0lsc0tt.   I know how to get the IP, gateway and subnet mask info on the PC.  Does anyone know where to display it on the Mac (OS 9.2)?  I'll post again tomorrow when I get the info from the PC and the Mac.
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Expert Comment

by:bstrauss3
ID: 16657973
Let's get some stuff straight here.

There are two ways for a network card to get an IP address.  One is via DHCP, the other is called static.

DHCP is a protocol which allows a card without an address to broadcast and say 'hey, what do I use'.  The address you receive (can) change each time.
Static assignments are fixed via software to a specific value.  The value never changes.

When you say "automatically assign the IP address", which do you mean?

It sounds like your DSL router is operating in bridge mode - not NAT.  If so, your ISP will have given you a range of IP addresses that are assigned to you, and you can use any/all of the addresses in that range - statically.  However, if that's the case, then you CAN NOT use DHCP.

(Well, it might work in that the ISP could be assigning you an address, but it will probably be in a small pool of last-resort type addresses, so there's little or no chance that your machines will know how to address each other).

-----Burton
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Author Comment

by:jimblunt
ID: 16658272
The ISP did give the client 5 static IP addresses.  I chose one and put the info into the router setup.
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Expert Comment

by:bstrauss3
ID: 16658664
That, then is probably your problem.  You need to confirm whether the DSL router is providing NAT (Network Address Translation) services.

If so, then each of the internal PCs should be using DHCP to receive an address in one of the private (RFC 1918) spaces, either 10.0.0.0/8, 172.16.0.0/16 or 192.168.0.0/16.

Using the private space will you probably still want to assign static addresses so the devices can talk to each other.


If the DSL router is NOT providing NAT (that is it is in bridge mode), then each of the internal PCs needs to be (statically) assigned a unique address in the block the ISP gave you.


-----Burton
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Expert Comment

by:CKWT
ID: 16663592
I believe a Router error is the problem with  configuration..

The router will not cause all PC's to loose connectivity but if you set a statip IP on the LAN or maybe you made the Scope too small you'll take away a given IP lease to a new request..

My recommendation:

Check router configuration like this:  

* WAN: Static IP from ISP and all it's config/DNS/Netmask/gateway.
*LAN: IP 192.168.1.1 and DHCP range 192.168.1.2 to 1.30 so you'll have more than 2 dozen IP addresses to lease from
          router.

in the network card interface enable Netbios over TCP/IP to do file sharing no matter the IP address of computer.
\\billing or \\192.168.1.7                  
\\accounting or \\192.168.1.8                   both will be a good way, when Static when DHCP try names better.


Hope to help

CKWT
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by:bstrauss3
ID: 16666960
One correction, CKWT: "you'll take away a given IP lease to a new request.."

Never happens.  That's is prohibited by the DHCP specification.

(1) When half the time of the lease (e.g. 3.5 days for a 7 day lease) has run, the client is supposed to contact the server to extend the lease.

(2) When the lease has expired including any extensions - and only then - can the address be returned to the pool by the server.  For the client to continue to use and expired lease is a violation of the spec.

(3) When offering a lease, both the server (albeit rarely done) and the client are supposed to explicitly check if the address is in use (say a static assignment of what is supposed to be a dynamic use or somebody continuing to use the leased IP).

If the server has no IPs to offer, it simply doesn't respond.

That said, for a small local situation NetBIOS over TCP/IP may be a work-around for the OP's problem.

-----Burton
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Author Comment

by:jimblunt
ID: 16673667
Client has a call in to ISP for tech support.  I'll see if that fixes it.  If not, I'll get back there next week and gather data as suggested and post results here.  Thanks to all!
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Expert Comment

by:CKWT
ID: 16673708
right Thanks for the correction, Can this be another DHCP probability, if the lease time is set to less than normal/usual/standard?.

CKWT
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Expert Comment

by:bstrauss3
ID: 16675079
No ... part of the DHCP offer is the lease time.

The flow is:

REQUEST - "Give me a lease"

OFFER (can be from one or more servers) - "Sure: How about a.b.c.d for 4 hours"

ACCEPT - "Server e.f.g.h, I'll take a.b.c.d for 4 hours"

-----Burton
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Author Comment

by:jimblunt
ID: 16787158
Solved the problem myself by manually assigning IP addresses in the 192.168.X.X range to each printer thru its control panel, with the help of a technician from the printer company.  Worked like a champ.
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Expert Comment

by:b0lsc0tt
ID: 16793818
@Netminder - I don't think this is very clear cut but in my opinion Bstrauss33's first comment is the answer.  A couple of his later comments and my comments added details but essentially the problem was incorrect IP's and his first comment points out that those will need to be changed.  I'll admit that actually applying the solution did take the help of a technician on the phone but we never did get the local IP's (PC, Mac and printers after the router was installed).  This appears to have been the key to the problem.

One short coming in our help was we were not able to tell him how to get the IP Config information from a Mac.  (I have gotten it before but can't do it from memory.)  In my opinion the question got off topic a bit with CKWT's comment (@CKWT - this is probably due to hindsight so please don't take that comment wrong.) and at the same time Jim was giving the information we needed to a phone technician.  I have no problem with Jim doing that since his problem is fixed but this is about cleaning the question.

If the question is kept then my suggestion would be:

http:Q_21845990.html#16653727 --> Accept
http:Q_21845990.html#16654036 --> Assist

I feel the only other option would be to Delete/Refund.  I hope this helps you and Jim to clean this up.  Thanks for your work!

bol
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Author Comment

by:jimblunt
ID: 16794394
I would have no problem splitting the points 50-50 as bolscott suggests.  Credit where credit is due kinda thing.
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