[TriLUG] Re: Fixed or dynamic IP addresses? Dual IP addresses on same port?

[Scott G. Hall]

Corey Mutter <mutterc at nc.rr.com> wrote:

>On Fri, Mar 28, 2003 at 07:54:46AM -0500, Scott G. Hall wrote:
>  
>
>>I also have a router/switch acting as an Internet gateway, firewall, and
>>DHCP server.  Currently all of the machines are configured to dynamically
>>get their IP addresses from the DHCP server on the router/switch.
>>
>>Now my dilemma: I want to startup FTP and HTTP servers on my private LAN,
>>as well as allow for the r* utilities (rlogin, rcp, etc) and NFS shares.
>>Do I still want to use dynamic IP addressing?  Or do I need to switch over
>>to only static addressing?
>>    
>>
>
>You can do both... most DHCP servers will allow you to configure things so
>that a particular machine (as measured by Ethernet MAC address) always gets
>the same address.
>  
>

The problem is this: when the Linux boxes receive their IP addresses
dynamically, they experience the problem.  Without a hosts table, they 
cannot
resolve their own name through gethostbyname(), much less find the others.
This is preventing any FTP or HTTP server from running (and I assume other
servers as well -- I'm going to add a local pop server to sort through email
retrieved rom boxes all over the 'net and also forwarded to us from our
registered (unhosted) domain).

What we did where I used to work, is that each machine that served up
services had a static IP address and hostname for the service.  This was
then maintained in a local hosts table that was then distributed to each
machine via NIS.  Then any machine that was to act as a workstation was
served by the DHCP server and received a dynamic address, but each 
maintained
it own identity (hostname).  Therefore, there were some machines that acted
as both servers and workstations, with two hostnames, two IP addresses --
one static, one dynamic -- and the workstation hostname (not the server
hostname) was the dual-machine's primary hostname, and also the one used
by the Lan Manager/Windows/SMB communications (various manger's Windows-only
boxes, and some Mac's; in fact the SMB sharing was the only way to pass
files among various user's desktops directly).  All of the dual server-
workstations used only a single physical interface, and had two driver-level
interfaces ARP'ed on them -- a static one and a dynamic one.

>If your router/switch doesn't have that kind of config option, and you 
>deploy a dhcpd on a Linux-like machine instead, you can just add something
>like the following to dhcpd.conf:
>
>--- cut here
># Laptop docking station
>host dock {
>  hardware ethernet 00:c0:4f:ee:01:e3;
>  fixed-address 192.168.1.4;
>}
>--- cut here
>
>Corey
>  
>

I was hoping to avoid using a PC as the DHCP server, because I take them
down and reconfig them too often.  The LinkSys unit is on a battery backup
with the ADSL modem and 16-port hub, so that network does not go down when
the power goes out.  I was hoping to work out the dual solution.  However,
since it is my home network, and noone in the Internet or elsewhere is going
to see it, and the hosts table is totally my own editing, and I just reread
the manual for the LinkSys unit for setting up VPN tunneling, I think I may
just go static IP's and be done with it.  After all, we are only talking
about maintaining the hosts table for 9 machines (13 if you include dual-
boots).  I still like the idea of dual-IP addresses for the one machine that
is spooling the 3 printers and will run the local HTTP and POP servers; and
for the other machine that is providing a ton of NFS shares (15 
harddrives --
3 SCSI cards).  I would like to separate the server and the workstation IP's
on these boxes.

-- 
Scott G. Hall,
Raleigh, NC, USA
ScottGHall at BellSouth.Net