[ipxe-devel] DNS resolution runs into timeout

Michael Brown mbrown at fensystems.co.uk
Fri Dec 6 14:48:51 UTC 2013

On 06/12/13 14:09, Sven Dreyer wrote:
> Am 06.12.2013 14:32, schrieb Michael Brown:
>> - RA and DHCPv6 seem to be advertising different DNS servers (check
>> "show net0.ndp/dns6" and "show net0.dhcpv6/dns6")
> You are right. But both of these nameservers are answering to queries,
> so I didn't see a problem with that.
>> - neither RA nor DHCPv6 is providing a global IPv6 address for iPXE
> With "global", do you mean a 2000::/3 address? Both radvd and
> wide-dhcpv6s provide addresses from the 2002:4db7:c08::/64 (my 6to4
> subnet) scope. That works with all IPv6 capable devices in my network up
> to now.

No; "global" as in "not link-local".

According to your screenshot, radvd is advertising only a single prefix 
2002:4db7:c08:1::/64, which is being advertised as *off*-link and 
autonomous.  The prefix 2002:4db7:c08::/64 is not being advertised at all.

Since no on-link autonomous prefix is available, iPXE has no way to 
generate an IPv6 address via SLAAC.

radvd is advertising that the network is unmanaged, i.e. that DHCPv6 is 
used to provide only configuration options (rather than IPv6 address 

I think other IPv6 devices on your network will be acquiring an IPv6 
address via SLAAC for the advertised off-link prefix 
(2002:4db7:c08:1::/64), but will then be attempting to forward all 
traffic via the router (even traffic for nodes on the same network). 
Your router is presumably issuing large numbers of ICMPv6 redirects to 
attempt to work around this problem.

iPXE's simplified IPv6 routing model will not cope with this 
configuration, which I would argue is a broken configuration anyway.

If you want to use SLAAC, then you need to configure radvd to advertise 
an on-link autonomous prefix ("AdvOnLink on" and "AdvAutonomous on"). 
If you want to use stateful DHCPv6 then you need to configure radvd to 
advertise the network as being managed ("AdvManaged on") and ensure that 
the wide-dhcpv6s has an address pool available.


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