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Slackware 8.0 DHCP sending wrong subnet.

By phil.hall ·
Hello all, we (that is to say, the company for which I am employed)
are having an interesting situation that I hope someone here has seen
before and can assist us with.

Thanks in advance for any help.

OK, here's the deal: recently we replaced our previous DHCP server
with a new one. The old server was NetWare Border Manager (version
3.x) and the new one is Slackware Linux 8.0 (with the default DHCP
daemon installed). The Kernel was upgraded to 2.4.17.

The problem we're having is this: some computers attached to our
network are receiving (or have received) incorrect information from
the DHCP server. The IP Address range is fine (172.16.x.x) but the
Subnet Mask, which should be 255.255.0.0 is being set to 255.0.0.0.

Has anyone seen this before and know how to rectify this? The
workstations that receive the DHCP leases are all Windows 95/98/2000.
The workstations that are receiving the problematic netmask are only
Win95/98.

Here's the relevant portion of our dhcpd.conf:

subnet 172.16.0.0 netmask 255.255.0.0 {
range 172.16.1.0 172.16.3.0;
option routers 172.16.0.1;
}

So you see, this should be fine. Basically, give each client a unique
IP Address between 172.16.1.0 and 172.16.3.0, inclusive; excepting for
Static IP Addresses (servers).

Yet, this setup is producing the error as indicated above.

Any ideas?
Thanks in advance.

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Slackware 8.0 DHCP sending wrong subnet.

by phil.hall In reply to Slackware 8.0 DHCP sendin ...

I'm upping the value hoping that it makes the top 5 overall questions and thereby increasing the number of people that can give ideas on how to fix this...

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Slackware 8.0 DHCP sending wrong subnet.

by phil.hall In reply to Slackware 8.0 DHCP sendin ...

Point value changed by question poster.

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Slackware 8.0 DHCP sending wrong subnet.

by phil.hall In reply to Slackware 8.0 DHCP sendin ...

I upped the points to all I can give...is there nobody who has seen this odd behavior?...

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Slackware 8.0 DHCP sending wrong subnet.

by maxwell edison In reply to Slackware 8.0 DHCP sendin ...

I’m somewhat shooting in the dark here since my answer is a result of only a little bit of research, some of which took me into unfamiliar territory. But your question was intriguing enough to spend a little time looking into it. Perhaps my answer touches upon a possible cause that may lead you or someone else in the right direction.

Is it possible that you have (perhaps inadvertently) implemented VLSM (Variable-length subnet masking)? VLSM means implementing more than one mask on the same major class of a network. Implementing different masks for the same major class requires a routing protocol that supports VLSM. Such routing protocols are called classless routing protocols. They carry the mask information along with the route advertisements therefore allowing for the support of more than one mask. Examples of classless routing protocols include OSPF, RIP version 2, Cisco's EIGRP, BGP and IS-IS.

In your case, the LAN segments should be numbered from 172.16.1.0/16 to 172.16.3.0/16.

Could it be that the segments are numbered with /16 and /8 instead of both /16?

Or could it be that there is a problem with the correct routing protocol?

Good luck,

Maxwell

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Slackware 8.0 DHCP sending wrong subnet.

by phil.hall In reply to Slackware 8.0 DHCP sendin ...

Hi Maxwell, unfortuantely, we don't use VLSM, all our routing is done statically, and we don't have a large WAN that would make use of OSPF or the rest. Sorry.

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Slackware 8.0 DHCP sending wrong subnet.

Could the Win 9.x clients be assigning themselves private addressess like 10.0.x.x or 192.168.x.x. (or you have a rogue DHCP server?) with the 255.0.0.0 subnet mask and then the DHCP server updates their IP but not the mask?
Is "Obtain an IP address automatically" selected on the IP Address tab in the TCP/IP Properties dialog box for the network card of the Win clients?
Which protocols are installed?
It seems like a private addressing CIDR issue. You want 172.16.x.x 255.255.0.0 as your private address scheme and the Win 9.x clients want 10.0.x.x 255.0.0.0 Have you run your network with the other private address schemes? Are there any static IP's conflicting with your scope? To rule out Private Addressing issues and make sure your Windows clients don't give themselves automatic private addresses: Run the Registry Editor and navigate to the HKEY_LOCAL_MACHINE\ SYSTEM\ CurrentControlSet\ Services\ Tcpip\ Parameters\ Interfaces\ Adapters key. Add a new value titled IPAutoconfigurationEnabled and set it to 0 (zero); make sure the data type is REG_DWORD. If you do that and still have the problem you have localized the DHCP server as the problem but from the info you gave it seems isolated to Win 9.x clients.

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Slackware 8.0 DHCP sending wrong subnet.

by Shanghai Sam In reply to Slackware 8.0 DHCP sendin ...

The clients affected are DCHP enabled in the 172.16.x.x range, there is only one DCHP server on our network (the new Slackware box), and the mask listed in the dchpd.conf is what should be sent to them. The protocols installed are: IPX 32-bit Protocol for the Novell NetWare client. IPX/SPX compatible Protocol, & TCP/IP. Also installed is File and Printer sharing for Microsoft Networks, the Novell Client 32, and Client for Microsoft Networks. (If I failed to mention that we are on a Novell Netware 5.1 network, I apologise.) Additionally we must authenticate to an NT/2000 domain. The only machines with static IP Addresses are our servers and a handful of printers (required by some of the programs we have on site.) We have learned that if we run winipcfg and release all and then renew, the problem is solved. This was not an issue prior to the replacement of the DHCP server.

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Slackware 8.0 DHCP sending wrong subnet.

by tsrl In reply to Slackware 8.0 DHCP sendin ...

hello friend.

the problem is simple. 95/98 clients cannot resolving the dhcp server details hence the error.

u have to do a small addition to your existing dhcp config in the server.


in order to work correctly with 95/98 clients the server must be able to send packets with the ip destination address of 255.255.255.255

Type: route add -host 255.255.255.255 dev eth0

If you get a message "255.255.255.255: Unknown host",
you should try adding the following entry to

your /etc/hosts file:

255.255.255.255 all-ones

Then, try:

route add -host all-ones dev eth0

or

route add 255.255.0.0 dev eth0
eth0 is of course the name of the network device you are using. If it differs change appropriately.


I hope your problem will be solved...revert back pls.

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Slackware 8.0 DHCP sending wrong subnet.

by phil.hall In reply to Slackware 8.0 DHCP sendin ...

Since the DHCP reaches all hosts fine, but sends out the wrong subnet mask, it's not a problem with multicasting, which DCHP does normally. We're beginning to think that the default DCHP daemon in Slackware 8.0 is faulty.

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Slackware 8.0 DHCP sending wrong subnet.

by phil.hall In reply to Slackware 8.0 DHCP sendin ...

At this point, we're considering replacing the DHCP daemon with another one, rather than use the default DCHP Daemon that ships with Slackware 8.0
Thanks to you all for your ideas.

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