Re: [lwip-users] DNS using Wired interface and PPP

[Sergey A. Borshch]

On 11.08.2019 20:48, address@hidden wrote:
> Am 11.08.2019 um 14:55 schrieb Sergey A. Borshch:
> > Hello everybody.
> >
> > My system has two network interfaces: main is wired Ethernet and backup is
> > cellular modem using PPPoS. I want to choose which interface to use by
> > netifapi_netif_set_default().
> >
> > The problem I expect that both interfaces got DNS servers addresses from
> > providers. It is possible that each of interface is connected to each own
> > subnetwork and each provider has it's own DNS servers in their subnetworks not
> > accessible from outside of subnetwork. It means that when I use wired Ethernet
> > interface I should use DNS servers supplied by Internet provider via DHCP and
> > using cellular modem interface I should use DNS severs supplied by cellular
> > operator via IPCP. What is correct way to do do such scenario in lwIP?
> >
> > As far as I understood lwIP architecture, it uses two global (system-wide) DNS
> > addresses (by default) and each interface overwrites them after getting new
> > values by DHCP/IPCP. So used DNS addresses depends on which interface got their
> > DNS addresses last.
>
> Well, I think you're right there. However, is this different on Linux or
> some other OS? I don't know if there's any standard way of solving this.
I don't know how it is implemented internally, but I see DNS addresses fields in 
every interface settings GUI in Linux Mint and Windows 7. Possibly lwIP also 
should have DNS addresses in netif structure and access them via netif_default 
in dns_send() and dns_backupserver_available()?

> This could be solved e.g. by adding an optional layer between dhcp.c and
> the call to dns_setserver() so that an application can override this,
> but I wouldn't want to solve this in a much different way than other
> stacks...
>
> Regards,
> Simon

--
Regards,
  Sergey A. Borshch            mailto: address@hidden
    SB ELDI ltd. Riga, Latvia