[K12OSN] DHCP and PXE with two different Class of IP address

John Lucas mrjohnlucas at gmail.com
Sat Dec 9 21:16:27 UTC 2006


Assuming that you can get all you need from the Windows DHCP service 
configured, and that the IPs are statically assigned (by MAC address), then 
there should be no impact from DHCP per se. In your initial posts, you made 
it sound as if modifying the main DHCP service was an unlikely possibility. 
Are there truly no routers on the inside of your network? If true this would 
eliminate the need for DHCP forwarding agents and simplify routing back to 
the LTSP server :-}

The impact on the net will be a huge jump in traffic: NFS, and X traffic 
primarily. RDP and ICA are less bandwidth intensive than X traffic. On a busy 
net with poor traffic isolation (like an unsegmented class B), this could be 
detrimental. TFTP traffic uses UDP for transport, and this is sensitive to 
any network shortcomings (e.g. noise and latency) too. Hey, you never know 
'til you try :-}

On Saturday 09 December 2006 1:49, Bert Rolston wrote:
> Thanks John.
>
> I knew it would be a political issue more than technical.
>
> Fortunately there is a good relationship with other parties. It's a
> matter of soothing jangling nerves and assuring them any change will
> have minimal impact, be easy to back out of, and won't bring anything
> down in a screaming heap.
> This is based on the assumption that ALL current issues are resolved.
>
> So what would be the impact on their current network setup by adding the
> necessary lines to their DHCP server?
>
> As I understand it this shouldn't have any effect on their network
> whatsoever. The lines will only determine how their DHCP server handles
> PXE requests. In other words, it SHOULD NOT introduce any extra
> instability to the network.
>
> Or could this effect their WinCE based 'slim' clients? It is my belief
> that they use RDP, which wouldn't be effectd.
>
> Thanks again for everyone's input.
>
> Cheers,
> Bert
>
> On Sat, 2006-12-09 at 12:21 -0400, John Lucas wrote:
> > No, you can't put two LANs on the same switch unless the switch has a
> > least two VLANs in it (LANs by definition are separate entities, more
> > than one LAN connected through routes is called an internetwork, with a
> > small "i").
> >
> > I sent a fuller reply directly to you (I forgot to include the list) on
> > some alternatives; but basically if you can't make changes to the net and
> > you can't change the DHCP service, then you won't be able to run diskless
> > terminals on the "one big net". This is not a technology problem but a
> > political/bureaucratic one.
> >
> > On Friday 08 December 2006 00:09, Bert Rolston wrote:
> > > Thanks John,
> > >
> > > The fact is THEY ARE having problems on the network. Their Exchange
> > > server was misbehaving today.
> > >
> > > I will insist they have ALL other problems on their network resolved
> > > BEFORE the K12LTSP server is installed. And I will be insisting on GOOD
> > > server grade hardware.
> > >
> > > This site had a Samba server that was installed on old hardware, with
> > > command line only administration. After the tech that set it up moved
> > > to a new job a hard drive failed. People blamed Linux and said it
> > > wasn't up to the job.
> > >
> > > I've seen one installation on another site removed because LINUX was
> > > blamed for network problems. The culprit was a Win95 proxy server with
> > > a failing hard drive.
> > >
> > > But back to the question.
> > >
> > > So what you were saying earlier is that on the K12LTSP server I set up
> > > 	- 1 NIC with a Class B address that matches their scheme,
> > > 	  connected to their physical media
> > > 	- 1 NIC with the standard K12LTSP Class C scheme connected to
> > > 	  the same physical media, through the same switch
> > >
> > > This should satisfy my customer's criteria.
> > >
> > > What will the MS DHCP server do when a PXE request comes from the old
> > > hardware?
> > >
> > > I may be answering my own question, as I understand things MS DHCP will
> > > ignore the request. Is that the case?
> > >
> > > As for the LTSP DHCP server, I take it I can tell it to IGNORE any DHCP
> > > requests from a host with an MS operating system.
> > >
> > > Thanks for your time.
> > >
> > > Cheers,
> > > Bert
> > >
> > > On Thu, 2006-12-07 at 22:18 -0400, John Lucas wrote:
> > > > Well you should be able to set up the LTSP server as a NAT firewall
> > > > through IPTables, or use a hardware NAT firewall in front of the
> > > > server; that way you can hide the terminals behind the server's IP
> > > > address and still make no changes to the rest of the network, while
> > > > still enabling you to run your own DHCP server for the terminals.
> > > >
> > > > BTW, a single net class B means that *all* hosts are in the same
> > > > broadcast domain. If you have over 250 hosts on that net, that is a
> > > > lot of broadcast traffic, one chattering NIC and the entire net feels
> > > > the pain. I wouldn't want to be a network support tech on that net if
> > > > anything goes wrong; that isn't the most robust net design. A netmask
> > > > of 20 bits would allow 16 subnets of 1024 hosts each and allow
> > > > sub-dividing the broadcast domain and isolate traffic behind routers
> > > > (as well as allow special subnets like yours without resorting to
> > > > NAT).
> > > >
> > > > On Thursday 07 December 2006 16:44, Bert Rolston wrote:
> > > > > Hi John,
> > > > >
> > > > > Thanks for your reply.
> > > > >
> > > > > The reason they went to a Class B scheme was to overcome the 254
> > > > > host limit.
> > > > >
> > > > > They are using a /16 subnet mask.
> > > > >
> > > > > The network in question is at a small tertiary educational
> > > > > establishment. It provides courses in business studies ( 1 lab),
> > > > > animation ( 2 labs), certificate in television production,
> > > > > christian ministry and counselling courses. Also running on the
> > > > > same network are campus admin, a small regional TV station, TV
> > > > > production and marketing company, an animation studio with render
> > > > > farm.
> > > > >
> > > > > Thanks for your time,
> > > > > Bert
> > > > >
> > > > > On Thu, 2006-12-07 at 12:54 -0400, John Lucas wrote:
> > > > > > You mentioned that the current network is using a class B address
> > > > > > scheme, but is that address space sub-divided? What netmask is
> > > > > > being used?
> > > > > >
> > > > > > Almost no one with a class B uses the 16-bit netmask; use of a
> > > > > > 24-bit netmask divides the single network into up, to 254 subnets
> > > > > > of up to 254 hosts each (a more useful scheme). Assuming that a
> > > > > > 24-bit (or larger) netmask *is* being used, how about creating a
> > > > > > new private (class-C sized) subnet on one NIC in an LTSP server,
> > > > > > and have another NIC attached to the existing network? This
> > > > > > allows the terminals to use
> > > > > > DHCP/tftp/PXE/etherboot from the LTSP server and still access the
> > > > > > MS Terminal server (using rdesktop) without changing the existing
> > > > > > network (save for the addition of the new LTSP server and it's
> > > > > > terminals). In this scenario the LTSP server could be used as a
> > > > > > router (for terminals running rdesktop sessions), or as a
> > > > > > dual-homed host (running rdesktop from the LTSP server itself).
> > > > > >
> > > > > > My choice would be to run rdesktop on the terminal (via the
> > > > > > SCREEN_x directive in lts.conf). This allows sound to be
> > > > > > re-directed from the MS TC to the terminal and preseves the
> > > > > > ability to run Linux on the LTSP server (via a separate SCREEN_x
> > > > > > directive). Thin clients are far simpler to maintain than
> > > > > > stand-alone PCs.
> > > > > >
> > > > > > On Thursday 07 December 2006 00:58, you wrote:
> > > > > > > Hey folks,
> > > > > > >
> > > > > > > I know this little chestnut has been chewed over many times on
> > > > > > > this list. I don't remember my situation coming up. So first
> > > > > > > I'll describe the environment.
> > > > > > >
> > > > > > > =======================
> > > > > > > The current environment
> > > > > > > =======================
> > > > > > >
> > > > > > > An MS Network with AD, terminal server and MS DHCP server with
> > > > > > > CLASS B IP address scheme.
> > > > > > >
> > > > > > > They want to revitalise their old Win 9x / NT machines and are
> > > > > > > investigating using K12LTSP or locally installed Linux. They
> > > > > > > have a lot of old classic to PII Pentiums which are gathering
> > > > > > > dust.
> > > > > > >
> > > > > > > One option is to boot the LTSP terminals in kiosk mode to
> > > > > > > access their Windows Terminal server using the RDP client
> > > > > > > included.
> > > > > > >
> > > > > > > The other option is to install a lightweight Linux distro
> > > > > > > (Puppy or DSL) on all the machines and use the RDP client that
> > > > > > > way.
> > > > > > >
> > > > > > > They don't want to change their existing infrastructure if at
> > > > > > > all possible. Even making changes to their DHCP server is
> > > > > > > considered risky by the network admin. ANY adverse impact on
> > > > > > > their existing system is unacceptable.
> > > > > > >
> > > > > > > The network admin uses Ubuntu at home, but has been unable to
> > > > > > > get any Linux computer to authenticate to the AD at work.
> > > > > > > For that reason he only sees limited potential for Linux / OSS
> > > > > > > in their current environment.
> > > > > > >
> > > > > > > Users will authenticate to their AD through Windows terminal
> > > > > > > sessions.
> > > > > > >
> > > > > > > Later on they may enable access to the Linux desktop and apps.
> > > > > > >
> > > > > > >
> > > > > > > =======================
> > > > > > > My Question
> > > > > > > =======================
> > > > > > >
> > > > > > > Given that the current DHCP server issues Class B addresses.
> > > > > > >
> > > > > > > Can the K12LTSP DHCP server, which issues Class C addresses
> > > > > > > 	- co-exist on the same physical media
> > > > > > > 	- handle PXE requests from the old hardware,
> > > > > > > 	- and not interfere with their current setup?
> > > > > > >
> > > > > > > If so what changes (if any) need to be made
> > > > > > > 	- on the MS DHCP server,
> > > > > > > 	- their current setup
> > > > > > > 	- the K12LTSP server
> > > > > > >
> > > > > > > Thanks,
> > > > > > > Bert
> > > > > > >
> > > > > > > _______________________________________________
> > > > > > > K12OSN mailing list
> > > > > > > K12OSN at redhat.com
> > > > > > > https://www.redhat.com/mailman/listinfo/k12osn
> > > > > > > For more info see <http://www.k12os.org>
> >
> > --
> >         "History doesn't repeat itself; at best it rhymes."
> >                         - Mark Twain
> >
> > | John Lucas                          MrJohnLucas at gmail.com              
> > | | St. Thomas, VI 00802               
> > | http://mrjohnlucas.googlepages.com/ | 18.3°N, 65°W                     
> > |   AST (UTC-4)                         |

-- 
        "History doesn't repeat itself; at best it rhymes."
                        - Mark Twain

| John Lucas                          MrJohnLucas at gmail.com               |
| St. Thomas, VI 00802                http://mrjohnlucas.googlepages.com/ |
| 18.3°N, 65°W                        AST (UTC-4)                         |




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