[mythtv-users] Questions on PXE booting a frontend

[Gareth Glaccum]

>from Jelta
I am surprised that this works. How do you prevent the router from assigning
an IP before your backend does? Or has it just been the luck of the draw,
and you have been lucky a lot?
---

I have the same setup. There is no reliance on luck. 
The PXE client in a machine, CANNOT accept a response from a dhcp server which does not specify a valid filename to download (part of the specs for PXE). 
If you watch the PXE client, you might see:

Gaining IP information from DHCP: ...-.-...

The . symbols are from each packet/timeout which is not responded to.
The - symbols are for each response received, which is invalid (i.e. no filename).
If you set up your diskless machine correctly, once it has the kernel and initrd, it doesn't matter which DHCP server responds, so long as the networking information allows the system to mount a rootfs somehow (either NFS server, or ISCSI, or tmpfs/rsync being the more popular choices). So basically, you can have a dynamic lease on the router, with a non-dynamic lease on the backend, both on the same subnet. The PXE can only work with the backend, and once the network is up, the machine shouldn't care if it's IP address changes (and it shouldn't happen, as most DHCP clients perform re-requests for leases from a specified DHCPSERVER [in the initial packet response] and the router should not respond to any non-broadcast requests). 

Regards, 
Gareth
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