News Group Posts

dhcp client dhcpd

From: Simon Hobson <simon@no-spam.ccomms.demon.co.uk>
Subject: Re: DHCP and such
Date: Sat, 24 Mar 2001 13:49:35 +0000
References: <%B8u6.19284$227.1707651@newsread2.prod.itd.earthlink.net>
<20010321164022.G77@jpradley.jpr.com>
<uLuu6.1815$ue1.114335@newsread2.prod.itd.earthlink.net> 

On Thu, 22 Mar 2001 22:10:34 +0000, Henna wrote
(in message <uLuu6.1815$ue1.114335@newsread2.prod.itd.earthlink.net>):

>>> Have Sco 5.0.5 Enterprise
>>> Want to look into using the OS for DHCP to windows 95/98 and 2000
> computers.
>>> 
>>> My want list would include:
>>> 
>>> To be able to pass out ip's to multiple ip's. For example
>>> 192.168.5.x
>>> 255.255.255.0
>>> 
>>> and
>>> 
>>> 192.168.10.x
>>> 255.255.255.0
>>> 
>>> and
>>> 
>>> 192.168.20.x
>>> 255.255.255.0
>>> 
>>> and be able to define default gateways, dns server and file/print
> shares.

> How do I setup the properties to automatically give a gateway, note that
> this gateway will change depending upon which router the client is behind.

You define each subnet in /etc/dhcpd.conf. When the DHCP server receives a 
request, it looks at the source to determine which subnet the client is on, 
and servs up an appropriate address. You do need bootp forwarding enabled on 
your routers for this to work.

For example :
subnet 192.168.10.0 {
        comment Remote Office A
        mask 255.255.255.0
        pool OfficeAPool
        routers router.sitea.somedomain.com
        dns_servers dns.somedomain.com
        domain sitea.somedomain.com
}

You repeat this section for each network, changing the routers address and 
domain name as appropriate. You can specify things like routers, dns servers 
etc by IP address or hostname - but ALL hostnames listed in the file must be 
resolvable or the dhcp server will stop processing requests. This cought me 
out when I removed a redundant domain from my DNS and forgot that it was 
referenced in the dhcp config !

You can configure the above either by editing /etc/dhcpd.conf, or by using 
the admin tools.

You need to set up an address pool in the Address Allocation Server for each 
network.

There are a lot of other options that can be set, including some netbios 
stuff that PCs use.

> How do I setup the properties to automatically setup the dns server, this
> will not change but I do not know how to do it in SCO.

I assume that what you mean is "how do I set it up to keep the dns server in 
sync with client addresses", unless it has changed from version 5.0.5a which 
we run, you can't.

There are two main reasons (plus a handful of minor ones) that I am in the 
process of moving DNS and DHCP to a Linux box :

1) Because the dhcp & aasd combination keeps lease information in what I 
assume is a SCO proprietry format, the dhcp-dns* utility does not work on SCO 
- therefore you cannot have dynamic DNS updates from dhcp to dns (unless 
someone tells me otherwise).
2) My experience is that the dhcp server does not handle remote networks 
properly. When I last tried it, I found that the server correctly determined 
the network, correctly allocated an address, but then tried to send the 
response to the device on the local network ! Hence, the client never got to 
see the dhcp offer.

* dhcp-dns is a set of scripts by Stephen Carville which periodically look at 
the dhcp leases file and use dynamic dns updates to add both the forward and 
reverse entries to dns. See http://www.cpl.net/~carville/dhcp-dns.html

Simon

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