Jason Bechtel wrote:
>
> David,
>
> I disagree very much. Please see my comments below...
>
> David Johnston wrote:
>> As I understand it, ltsp uses dhcp in part to make IP address
>> assignments completely automatic. Infinite leases break this by
>> preventing address recycling.
> LTSP uses bootp just as well as DHCP (and bootp is anything but
> automatic).
A good point.
> Since many (probably the great majority of) LTSP environments are not
> done with uniform hardware in the workstations, one needs to specify
> different video, NIC, and perhaps kernel file settings for different
> workstations.
That's not so true with version 3. The autodetection seems to work
fairly well.
> If by "address recycling" you are talking about having LTSP workstations
> receive effectively randomly assigned IP addresses (and therefore
> hostnames via DNS/hosts) then the functionality of the lts.conf file is
> broken
No, that's not what I meant. One of the fundamental advantages of LTSP
is that the terminals can be (and generally are) old equipment. This
means that they are inexpensive, but prone to failure. When a terminal
does fail (as I expect and plan for), I want to be able to tell someone
to grab a spare from the closet and stick it on the desk. I want
terminal installation to be so simple, even a pointy-haired boss can't
screw it up. This lowers failure cost and downtime, which I consider a
major selling point for LTSP.
> ...all of the LTSP setups I've been involved in have had entries that
> match a MAC address to a fixed IP address, hostname, and kernel (either
> through bootp or DHCP). ... But for LTSP clients, there is no dynamic
> assignment whatsover.
This is fine, but it increases network management, something I'm trying
to get away from.
> (DHCP is more flexibile)
No argument from me on this.
>> As long as the dhcp server stays up, the only downside to lease
>> expirations is a few UDP packets between the workstation and the server
>> at lease renewal. Most of the time, a given workstation will get the
>> same address every time.
>>
>> In a production environment, there are many justifications for leaving
>> your servers up all the time and few for leaving them down most of the
>> time.
>
> Yes, the original context of this discussion was someone who would shut
> down their DHCP server after booting up his one client. This is a
> strange case and obviously not relevant to corporate use. But *if* we
> can satisfy all customers with one catch-all default setting (always
> allowing for someone to be able to change from the default), then we
> should do that.
I agree, one catch-all default is a good idea. We simply disagree
regarding the usefulness of this specific default. I still argue that,
in a normal work environment, dynamically assigned IP addresses with a
one week lease provides a good approximation of static IP addressing
without needing any oversight.
> If you have a pool of LTSP workstations and are handling IP addresses
> dynamically...
>
> 1) I'd love to hear how you are pulling it off. How do you assign hostnames?
Are they necessary?
You can use nsupdate at login time to map hostname=username (this one
has problems, of course), or you can simply name them ws001, ws002, etc,
based on the last octet of the IP address.
> 2) Why bother? Just set aside a block of addresses to be assigned
> statically to your LTSP clients. What do you gain with dynamic address
> allocation if you always have the same number of clients?
See my comments above. I am assuming that, since they are doorstops I
rescued from the trash, the terminals are going to fail regularly. When
they do fail, I want replacing it to be a no-brainer; in particular, I
don't want to have to give anyone a password so they can muck around in
my dhcp config or lease files.
> I suppose avoiding the tedium of having to collect all of the MAC
> addresses and information about their corresponding hardware would be a
> good reason to do this.
Yes, another point at which LTSP reduces network management.
> Then you would only need to get MAC addresses for clients who deviate
> from the norm. But now we're talking about making the default response
> of the DHCP server (regardless of the MAC address of the client) one that
> handles LTSP workstations. Doesn't this seem just as imposing as specifying
> an inifinite lease time?
Not quite. Assume a class C network with 250 terminals. Three failed
terminals, and someone who knows what they are doing (=$$$) has to clean
up the dhcp files before a fourth terminal can be dropped in.
For example, the network 192.168.1.0:
192.168.1.1 through 192.168.1.250 are terminals
192.168.1.251 through 192.168.1.253 are "spare" addresses
192.168.1.254 is the LTSP server as well as the gateway to the rest of
the network.
If 192.168.1.52 fails, the replacement will get 192.168.251. Nothing
will ever get 192.168.1.52.
Once the three "spare" addresses are used, I (or someone else who
understands dhcp files) has to clean up.
On the other hand, if we use weekly leases then #52's IP is available
about a week after failure. This is completely automatic and requires
no intervention, which means that, in the long run, it is cheaper to
maintain.
Every installation has its quirks. However, I like LTSP because it
significantly reduces maintenance costs by allowing me to run networks
on autopilot most of the time.
-David
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