[Dnsmasq-discuss] dnsmasq sending truncated DHCPv6 packets

[Geert Stappers]

On Fri, Nov 29, 2019 at 03:55:17PM +0000, Derek Higgins wrote:
> Hi,
> 
> I've been trying to track down the reason for intermittent PXE
> failures while using DHCPv6,
> the failed PXE attempts seem to correlate with incomplete dhcp6
> advertise packets.
> 
> e.g. in this sequence, the advertise packet length is 62 (all of the
> failed attempts I've found happened with packets of the same length)
> 
> 14:11:42.843363 00:93:12:a1:39:68 > 33:33:00:01:00:02, ethertype IPv6 (0x86dd), length 116: fe80::293:12ff:fea1:3968.546 > ff02::1:2.547: dhcp6 solicit
> 14:11:42.843598 52:54:00:96:ef:51 > 00:93:12:a1:39:68, ethertype IPv6 (0x86dd), length 62: fe80::5710:879f:72e4:7b41.547 > fe80::293:12ff:fea1:3968.546: dhcp6[|dhcp6]
> 
> Compared to a successful sequence
> 14:11:44.843012 00:93:12:a1:39:68 > 33:33:00:01:00:02, ethertype IPv6 (0x86dd), length 116: fe80::293:12ff:fea1:3968.546 > ff02::1:2.547: dhcp6 solicit
> 14:11:44.843247 52:54:00:96:ef:51 > 00:93:12:a1:39:68, ethertype IPv6 (0x86dd), length 168: fe80::5710:879f:72e4:7b41.547 > fe80::293:12ff:fea1:3968.546: dhcp6 advertise
> 
> I've attached 3 files, the first is my dnsmasq config file, the second
> is my dnsmasq logs and the 3 is a tcpdump of the DHCPv6 traffic while
> 3 hosts were PXE booting one succeeded and the other 2 failed in the
> way described above
> 
> I'm using dnsmasq-2.76-10.el7_7.1 on CentOS 7.7.1908 running in a container

And what is at client side?


> I've also tried with the most recent version of dnsmasq
> (2.80-93-g6ebdc95), and also get strange looking packets
> (msgtype-134??), eg
> 10:40:43.204829 00:39:a6:0a:33:99 > 33:33:00:01:00:02, ethertype IPv6 (0x86dd), length 223: fe80::239:a6ff:fe0a:3399.546 > ff02::1:2.547: dhcp6 request
> 10:40:43.206361 52:54:00:02:9a:11 > 00:39:a6:0a:33:99, ethertype IPv6 (0x86dd), length 126: fe80::5325:ca30:6ccd:c83.547 > fe80::239:a6ff:fe0a:3399.546: dhcp6 msgtype-134
> vs.
> 10:40:43.213256 00:39:a6:0a:33:95 > 33:33:00:01:00:02, ethertype IPv6 (0x86dd), length 223: fe80::239:a6ff:fe0a:3395.546 > ff02::1:2.547: dhcp6 request
> 10:40:43.219308 52:54:00:02:9a:11 > 00:39:a6:0a:33:95, ethertype IPv6 (0x86dd), length 210: fe80::5325:ca30:6ccd:c83.547 > fe80::239:a6ff:fe0a:3395.546: dhcp6 reply
> 
> but these only appear to happen after iPXE has chain loaded and also
> sometimes stalls the boot process, I guess depending on when they
> happen.


Regards
Geert Stappers