@Tom-Elliott YESSSSSS!!! I commented out line "port=0 ", and…voilá! I have full clonning system working, with fog machine capable to access the internet!
Thanks a lot my friends!

SOLVED!

@Tom-Elliott Hi Tom. Thanks for answering. Do you mean this line?:

• Don’t function as a DNS server:
  port=0

I have that line uncommented, I mean, it is runnning.

So you thought you´ll get rid of me easyly!..No sir, here I am again!..And of course…with troubles!
My old “dnsmasq issue” about the bug of the pxe boot file name (undionly.0 instead of undionly.kpxe) was solved, and my settings to make Fog work on my lan combined with my TPLINK router and its dhcp server works great!
Now, the new point is: when the ltsp.conf file is present (at /etc/dnsmasq.d), the fog clonning system works fine. But fog server machine LOSES INTERNET ACCESS!
But if I delete the ltsp.conf file and leave the dnsmasq.d folder empty, fog machine RECOVERS INTERNET ACCESS!
So, this make me think I could add a line or lines to ltsp.conf file, in order to keep Internet access. Is this correct? Whis are this lines? Or how to achive this?
Internet supplied by tplink router with dhcp embeded.
Thanks in advance to all of you.

@pabloinza Hi my friends. Finally i could solve this changing Ubuntu to ver 12.04. Here muticast works fine.

@Wayne-Workman Wayne!!..Ah ah!!..Savior of the Universe! Finally the solution! It finally works! I think the error is an issue of dnsmasq, since when I tried all of this stuff configuring Fog server machine as dhcp server, all worked fine, and in the dhcpd.conf file, the proper line said “undionly.kpxe”. So, I think dnsmasq is who´s mistaking the name of the file.
Well, what ever, it works!
Thanks a lot my friend! I really appreciate your help.
I don´t know how to tag this post as “SOLVED”. Would you please tell me?

@Wayne-Workman I´ve tried changing the line:

• dhcp-boot=pxelinux.0
  to
• dhcp-boot=undionly.kpxe
  and then the clients say “tftp file not found”

@Wayne-Workman Yes Wayne, I suppose that. In fact, I read that in this forum. But with my pour knowledge about Linux and all of this, I can´t achieve this. Would you please type for me the EXACT lines I need to put in my ltsp.conf file, and in any other place what ever I need to type or add or delete?

@Wayne-Workman Here is the screen capture of a pxe clien during boot process. This is the farther point I could reach

And if I change pxelinux.0 by undionly.kpxe, then it says “tftp file timeout, pxe file not found”

@Wayne-Workman Here is my ltsp.conf file:

- Sample configuration for dnsmasq to function as a proxyDHCP server,
- enabling LTSP clients to boot when an external, unmodifiable DHCP
- server is present.
- The main dnsmasq configuration is in /etc/dnsmasq.conf;
- the contents of this script are added to the main configuration.
- You may modify the file to suit your needs.



- Don't function as a DNS server:
port=0

- Log lots of extra information about DHCP transactions.
log-dhcp

- Dnsmasq can also function as a TFTP server. You may uninstall
- tftpd-hpa if you like, and uncomment the next line:
- enable-tftp

- Set the root directory for files available via FTP.
tftp-root=/tftpboot

- The boot filename.
dhcp-boot=pxelinux.0

- rootpath option, for NFS
dhcp-option=17,/images

- kill multicast
dhcp-option=vendor:PXEClient,6,2b

- Disable re-use of the DHCP servername and filename fields as extra
- option space. That's to avoid confusing some old or broken DHCP clients.
dhcp-no-override

- PXE menu.  The first part is the text displayed to the user.  The second is the timeout, in seconds.
pxe-prompt="Press F8 for boot menu", 3

- The known types are x86PC, PC98, IA64_EFI, Alpha, Arc_x86,
- Intel_Lean_Client, IA32_EFI, BC_EFI, Xscale_EFI and X86-64_EFI
- This option is first and will be the default if there is no input from the user.
pxe-service=X86PC, "Boot from network", pxelinux

- A boot service type of 0 is special, and will abort the
- net boot procedure and continue booting from local media.
pxe-service=X86PC, "Boot from local hard disk", 0

- If an integer boot service type, rather than a basename is given, then the
- PXE client will search for a suitable boot service for that type on the
- network. This search may be done by multicast or broadcast, or direct to a
- server if its IP address is provided.
- pxe-service=x86PC, "Install windows from RIS server", 1

- This range(s) is for the public interface, where dnsmasq functions
- as a proxy DHCP server providing boot information but no IP leases.
- Any ip in the subnet will do, so you may just put your server NIC ip here.
- Since dnsmasq is not providing true DHCP services, you do not want it
- handing out IP addresses.  Just put your servers IP address for the interface
- that is connected to the network on which the FOG clients exist.
- If this setting is incorrect, the dnsmasq may not start, rendering
- your proxyDHCP ineffective.
dhcp-range=10.10.10.101,proxy

- This range(s) is for the private network on 2-NIC servers,
- where dnsmasq functions as a normal DHCP server, providing IP leases.
- dhcp-range=192.168.0.20,192.168.0.250,8h

- For static client IPs, and only for the private subnets,
- you may put entries like this:
- dhcp-host=00:20:e0:3b:13:af,10.160.31.111,client111,infinite

Mod edited to use code box

@Wayne-Workman. Okay, but how come? The escenario works great if I disconnect the tplink router, connect all pc to a standard switch, and set the fog server pc as dhcp server; and there I don’t turn off anything, I don’t need to touch the fog server, default installation. So, why the need to touch its firewall?