[Udpcast] Timing problem with starting PXE boot and udp-sender

Alain Knaff alain.knaff at lll.lu
Thu Apr 29 21:02:28 CEST 2004

begin  Thursday 29 April 2004 18:50, Donald Teed quote:
> If 15 machines are booted, and set to go into receive mode,
> and udp-sender is run on the imaging server, and 4 clients
> need to be rebooted to restart PXE, we have noticed that we
> see a list of only the first 11 machines on the ready list from
> udp-sender, even after the remaining 4 have come up and show
> that UDP receiver is ready (but does not display "hit any key
> to start" on the remaining 4).

No idea what is going on here, possibly it is related to the problems
seen earlyer (slow card initialization).

> It seems like there is a window of a few minutes before the
> udp-sender will stop listening for more udp-receivers to say
> they are ready.

No, UDP-Sender listens for new receivers all the time.

However, when it first starts up, it also sends out a probe packet
(hello) to get any receivers to register, that might have started up

The idea is simple:
 - when receiver starts, it sends out CONNECT packet
 - when sender starts, it sends out HELLO packet
 - on recept of HELLO, receiver tries CONNECT again.

With this, it does not matter whether receivers or senders are started
up first, at least in theory:
 - if receiver starts first, it's the sender's HELLO that triggers the
successful rendez-vous
 - if on the other hand the sender starts first, it's the receiver
CONNECT that triggers the rendez-vous.

Now, in your case, what may be happening is the following:

- due to the flakiness of the card, the card may not yet be ready to
send once udp-receiver starts up, and thus the CONNECT is not really
sent. In case you start the sender afterwards, this doesn't matter,
because by the time the sender sends it HELLO, the receiver is ready
to receive that message and reply to it.
- for those receivers that needed a reboot: if these start after the
sender, there is no HELLO.

> I checked the options and I don't see any that are designed to increase
> how long it will wait to see more machines responding as ready.

There is  the "--rexmit-hello-interval 3000" option which instructs
the sender to keep on resending its HELLO packets until transmission
is started. The number is the interval, in milliseconds, between to
HELLO packets. This might solve the issue.

udp-sender --rexmit-hello-interval 3000 --file fileimage.gz



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