[Cialug] SOT: DHCP client address acquisition speed

[Paul Gray]

Nathan C. Smith wrote:
> What kinds of things on a network can affect the time it takes for a client to acquire a DHCP lease?
>
> When I PXE boot it seems to take 20-40 seconds for a machine to get a lease, is that "normal"?  Windows machines seem to pick up leases in a reasonable amount of time.
>
> Does the architecture of the network - number of switches, etc, have a bearing on the time to get a DHCP lease?
>   

When you PXE boot, you do a two-phase (a) here's your IP address, go ask 
Bob for your boot image (b) here's your boot image from bob. The PXE 
process isn't satisfied to just get an IP address, it waits and waits 
for another server to chime in with a next-server response in the packet.

The tftp server (aka "Bob" above), when dishing up the image, traverses 
the MAC and IP address byte-by-byte looking for an appropriate image to 
server out. So there is added overhead involved in the PXE process over 
just dhcp'ing an IP address.


I don't know if there's 20-40 seconds of extra overhead here, but 
there's the potential of 20-40 seconds of overhead if the tftp server 
isn't responding.

-PG