Re: [lwip-users] DHCP on multiple interfaces

[address@hidden]

Am 11.03.2019 um 11:29 schrieb Toby Duckworth:
> I am updating our code to support multiple simultaneous network interfaces,
> and have a question relating to DHCP.
>
> Before calling dhcp_start(...) we call netif_set_default(...) - Is this
> strictly necessary?

These two are different things. DHCP assigns an address, 
netif_set_default() sets up the default route (the netif that is used 
when targeting addresses outside the subnet of any netif).

DHCP does not need a default route to work. Maybe your application needs 
it though.

> If I remove the call to netif_set_default, then DHCP doesn't appear to work
> correctly.

That would really suprise me.

> With the net_set_default(..) call in place, DHCP works correctly, but
> (perhaps obviously) only on one interface at a time. Furthermore, having

No, not obviously.

> obtained an IP address, we then go on to call netconn_new(...) to create a
> Netconn on it, and find that unless netconn_bind_if(...) is called on the
> created netconn, then subsequent attempts to DHCP on a different interface
> cause problems for that netconn.

That sounds strange.

> I would like to understand better the expected behaviour of LWIP with
> respect to multiple network interfaces. and in particular how the DHCP
> process is meant to work:
>
> 1) Is a call to netif_set_default(..) required before calling
> dhcp_start(..)?

No.

> 2) Is it possible for multiple network interfaces to DHCP simultaneously?

Yes.

> 3) Is a call to netconn_bind_if(...) necessary if we want to guarantee that
> packets are sent and received using a particular network interface?

Yes!

Regards,
Simon