[Dnsmasq-discuss] how to configure lot of static routes

[Albert ARIBAUD]

Bonjour Maciej,

Le Tue, 30 Jun 2015 15:56:36 +0200, Maciej Soltysiak
<maciej at soltysiak.com> a écrit :

> On Tue, Jun 30, 2015 at 3:24 PM, Albert ARIBAUD <albert.aribaud at free.fr>
> wrote:
> 
> > Bonjour Michał,
> >
> > Le Tue, 30 Jun 2015 13:54:11 +0200, Michał Lipka <michal at lipka.email> a
> > écrit :
> >
> > > 2015-06-30 12:10 GMT+02:00 Maciej Soltysiak <maciej at soltysiak.com>:
> > >
> > > > On Tue, Jun 30, 2015 at 4:03 AM, wkitty42 at gmail.com <
> > wkitty42 at gmail.com>
> > > > wrote:
> > > >
> > > >>
> > > >> On 06/29/2015 04:01 PM, Michał Lipka wrote:
> > > >>
> > > >>>
> > > >>> 2015-06-25 16:02 GMT+02:00 wkitty42 at gmail.com
> > > >>>     does breaking the line work?
> > > >>>
> > > >>>     eg:
> > > >>>     dhcp-option=249,10.0.0.1/32,1.2.3.4,192.168.13.15/32,1.2.3.4
> > > >>>     <http://10.0.0.1/32,1.2.3.4,192.168.13.15/32,1.2.3.4>, \
> > > >>>     192.168.13.16/32,1.2.3.4,192.168.13.17/32,1.2.3.4
> > > >>>     <http://192.168.13.16/32,1.2.3.4,192.168.13.17/32,1.2.3.4>, \
> > > >>>     192.168.13.18/32,1.2.3.4,192.168.13.19/32,1.2.3.4
> > > >>>     <http://192.168.13.18/32,1.2.3.4,192.168.13.19/32,1.2.3.4>, \
> > > >>>     192.168.13.20/32,1.2.3.4 <http://192.168.13.20/32,1.2.3.4>
> > > >>>
> > > >>>
> > > >>> Thank you for this idea. Unfortunately it does not work. dnsmasq
> > fails
> > > >>> at first
> > > >>> line which has no option:
> > > >>>
> > > >>
> > > >> sounds like an option that should maybe be implemented... especially
> > > >> since it is an apparent standard that so many tools do follow ;)
> > > >>
> > > > I think dnsmasq has a 1024 characters for config lines. I browsed the
> > > > source briefly last night but couldn't find it.
> > > >
> > >
> > > I checked it more precisely and it turned out that is not line length
> > that
> > > bothers dnsmasq. It's routes count.
> > > I can set up to 28 routes in single dhcp-option line. It doesn't matter
> > if
> > > it will take 600 or 800 characters. If I set 29th route dnsmasq complains
> > > about option too long:
> > >
> > > dnsmasq: dhcp-option too long at line 320 of /etc/dnsmasq.conf
> > > Can you check the code once again and try to find this limit (28) ? Why
> > it
> > > is like that?
> >
> > Could it be that the total DHCP packet size goes over the maximum
> > allowed size for an UDP frame?
> >
> Perhaps. The offending code is related to the length of the dhcp option,
> not the number of routes per se:
> 
>   if (!is6 &&
>       ((new->len > 255) ||
>       (new->len > 253 && (new->flags & (DHOPT_VENDOR | DHOPT_ENCAPSULATE)))
> ||
>        (new->len > 250 && (new->flags & DHOPT_RFC3925))))
>     ret_err(_("dhcp-option too long"));
> 
> I guess you can stick more than 255 bytes in a dhcp packet, anyone knows if
> the limit is coming from RFCs or elsewhere?

There is actually an option's size limit, see RFC 2132 section 2:
the option second byte contains the length and its content does not
include the tag and length fields, so the actual option content cannot
be bigger than 253 bytes.

> Best regards,
> Maciej

Amicalement,
-- 
Albert.