[syslinux] tftpd and broadcast

[Geert Stappers]

On Mon, Sep 04, 2006 at 06:11:49PM +0200, Geert Stappers wrote:
> On Thu, Mar 23, 2006 at 03:43:20PM +0100, Geert Stappers wrote:
> > On Wed, Mar 22, 2006 at 07:49:33AM +0100, Radek Vokál wrote:
> > > Why tftpd doesn't support request from clients trying to tftp to the 
> > > broadcast address? Will this feature ever appear in tftpd? Or is there 
> > > any workaround for serving broadcast requests?

I think I begin to understand to question better, but still in doubt.
Now the original poster CCed to ask for elaborating the situation.


> > There are TFTP server that do answer "broadcasting" clients,
> > but that doesn't help tftpd-hpa (afterall we are on the tftpd-hpa ML ).
> > 
> > Early versions of DHCP programms were needing the IP-address
> > 255.255.255.255. (I don't remember which side (server or clientsss))
> > 
> > I suggest to setup the TFTP server with that broadcast address,
> > to find out if does help to serve the screaming TFTP clients.
> 
> No need for that suggeted workaround.

I wonder if it was tried ...


> I can confirm that version 0.42 of the HPA tftp daemon
> does reply to broadcasts.

Yes, it does reply to broadcasts, but fails on further follow-up.

Below is what I see with a ethernet sniffer like tcpdump.
The filter was set on the MAC address of the netbooting Sun UltraSparc5,
which got it IP-address .15 by RARP from 172.24.0.10.
At address .26 is the HPA tftp daemon which has the file AC18000F.
172.24.0.39 is another tftpd-hpa but hasn't the requested file.


19:17:35.232058 rarp who-is 08:00:20:a8:fc:fd tell 08:00:20:a8:fc:fd
19:17:35.234442 rarp reply 08:00:20:a8:fc:fd at 172.24.0.15
19:17:35.237505 IP 172.24.0.15.14671 > 172.24.0.10.69:  17 RRQ "AC18000F" octet 
19:17:35.240465 IP 172.24.0.10.3035 > 172.24.0.15.14671: UDP, length 19
19:17:40.239974 arp who-has 172.24.0.15 tell 172.24.0.39
19:17:41.239871 arp who-has 172.24.0.15 tell 172.24.0.39
19:17:42.239790 arp who-has 172.24.0.15 tell 172.24.0.39
19:17:53.294672 IP 172.24.0.15.14671 > 255.255.255.255.69:  17 RRQ "AC18000F" octet 
19:17:53.301110 arp reply 172.24.0.15 is-at 08:00:20:a8:fc:fd
19:17:53.301156 IP 172.24.0.39.3035 > 172.24.0.15.14671: UDP, length 19
19:17:53.308403 IP 172.24.0.26.33375 > 172.24.0.15.14671: UDP, length 516
19:17:54.305522 IP 172.24.0.26.33375 > 172.24.0.15.14671: UDP, length 516
19:17:56.305735 IP 172.24.0.26.33375 > 172.24.0.15.14671: UDP, length 516
19:17:58.305811 arp who-has 172.24.0.15 tell 172.24.0.26
19:17:58.324567 IP 172.24.0.15.14671 > 172.24.0.26.33375: UDP, length 4
19:17:58.324688 IP 172.24.0.26 > 172.24.0.15: ICMP 172.24.0.26 udp port 33375 unreachable, length 40
19:17:58.329974 arp reply 172.24.0.15 is-at 08:00:20:a8:fc:fd
19:17:58.335506 IP 172.24.0.15.14671 > 172.24.0.26.33375: UDP, length 4
19:17:58.335629 IP 172.24.0.26 > 172.24.0.15: ICMP 172.24.0.26 udp port 33375 unreachable, length 40
19:17:58.340920 arp reply 172.24.0.15 is-at 08:00:20:a8:fc:fd
19:17:58.346284 arp reply 172.24.0.15 is-at 08:00:20:a8:fc:fd
19:17:58.351854 IP 172.24.0.15.14671 > 172.24.0.26.33375: UDP, length 4
19:17:58.351971 IP 172.24.0.26 > 172.24.0.15: ICMP 172.24.0.26 udp port 33375 unreachable, length 40
19:17:59.305915 arp who-has 172.24.0.15 tell 172.24.0.26
19:18:00.306049 arp who-has 172.24.0.15 tell 172.24.0.26
19:18:00.306207 IP 172.24.0.26.33375 > 172.24.0.15.14671: UDP, length 516
19:18:00.310622 IP 172.24.0.15.14671 > 172.24.0.26.33375: UDP, length 4
19:18:00.310733 IP 172.24.0.26 > 172.24.0.15: ICMP 172.24.0.26 udp port 33375 unreachable, length 40
19:18:04.325325 IP 172.24.0.15.14671 > 172.24.0.26.33375: UDP, length 4
19:18:04.330666 arp reply 172.24.0.15 is-at 08:00:20:a8:fc:fd
19:18:04.330790 IP 172.24.0.26 > 172.24.0.15: ICMP 172.24.0.26 udp port 33375 unreachable, length 40
19:18:08.307169 IP 172.24.0.26.33375 > 172.24.0.15.14671: UDP, length 516
19:18:08.308876 IP 172.24.0.15.14671 > 172.24.0.26.33375: UDP, length 4
19:18:08.308996 IP 172.24.0.26 > 172.24.0.15: ICMP 172.24.0.26 udp port 33375 unreachable, length 40
19:18:12.318981 IP 172.24.0.15.14671 > 172.24.0.26.33375: UDP, length 4
19:18:12.319074 IP 172.24.0.26 > 172.24.0.15: ICMP 172.24.0.26 udp port 33375 unreachable, length 40


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Cheers
Geert Stappers