[Dnsmasq-discuss] rfc3527 support

[Simon Kelley]

Takayuki Kaiso wrote:
> Hi, Simon
> 
>  Thank you for your suggestion.
>   let me explain more details.
> 
> < configuration >
>      1.  DHCP client  is iPod touch   (supposed to be get 192.168.5.x
> from DHCP server )
>      2.  DHCP relay is running on a WiFi AP (AP is 192.168.5.1 and
> another interface
>                connected to the DHCP server is 10.0.1.82 ).
>                RFC3527 is implemented on this relay.
>      3.  DHCP server (actually, dnsmasq) is running on a openwrt
> embedded board.
>             it is connected to DHCP relay and the interface is
> configured 10.0.1.81
> 
>       therefore, giaddr is 10.0.1.82 and SUBNET_SELECT address is
> 192.168.5.1
>       in DHCPDISCOVER message.
> 
> < problem summary >
> 
>      - iPod send DHCPDISCOVER and received DHCPOFFER, but in the DHCPOFFER
>        message, siaddr field is blank and Server identifier option field
> has 0.
>        I believe both of these field must have valid address in DHCPOFFER.
> 
>        When iPod received such incomplete reply, it did not send
> DHCPREQUEST.
> 
>     - I used wireshark to investigate the those problematic field in
> DHCPDISCOVER and
>       DHCPREQUEST.
> 
> < investigation around the source codes >
> 
>      - Yes, I looked around line216 and  line 2216  in rfc2131.c
>         and also put some prrinf for debugging.
>      -  such debugging showed me context-local was 0
>          even though codes in rfc2131 successfully located the
>          target context using SUBOPT_SUBNET_SELECT.
> 
>      -   Why context-local was 0 ?   then I looked into dhcp.c to find
>           the place the context filed is built.
>           I think it is complete_context() function, then I put printf
> debugging here again
>           and found  it failed to locate the target context because
> param-relay.s_addr
>           is 10.0.1.82.
> 
> I am not confident that my patch is clean because I have not yet had
> big and precise picture on those codes.  So please correct me if I miss
> something.
> 
> I updated dhcp.c in my patch because context-router and context-local
> are checked in other places and (ex. line 968 in dhcp.c ) and I thought
> setting up those two fields in dhcp.c looks safer for me.
> 
> I definitely need your suggestion, Simon.
> 
> Thanks
> Takayuki Kaiso
> 
> 

The "server identifier is zero when using a DHCP relay" rings bells.
This came up here:

http://lists.thekelleys.org.uk/pipermail/dnsmasq-discuss/2011q1/004806.html

and was fixed the 2.58test series:

http://www.thekelleys.org.uk/dnsmasq/test-releases/dnsmasq-2.58test6.tar.gz

I don't think your problem is identical, but it may very likely have the
same underlying cause and the difference in symptoms is because you are
using subnet select. Please could you try dnsmasq-2.58test6 as a
baseline, and we'll take the debugging process from there?

Cheers,

Simon.