Re: [lwip-users] PPP proxy arp support

[Sylvain Rochet]

Hi,

On Wed, Oct 10, 2018 at 03:13:56PM +0200, address@hidden wrote:
> 
> Isn't proxy ARP support only really valid when we are a PPP server? That
> wasn't working at that time.

We use to call that client and server but in the end it is just an IP 
tunnel and both ends are equal, PPP protocol is mostly (fully if no 
corner cases are to be found :>) symmetric regarding which one is the 
initiator (e.g. IP addresses are not necessarily given by the initiator, 
both ends can even choose their own if remote side allow to do so). So 
technically speaking there is no reason for a PPP "client" or I would 
rather say non-initiator to never need ARP proxy. However I agree that's 
an option for IP routers so it makes more sense in the real world on 
what we call PPP "servers".


> >Was curious to know if this is something that, if the surrounding
> >`#define`s were removed, would likely just work,
> 
> No, the ARP layer does not have support for this. You'd have to add at least
> that to make it work.
> 
> >or if there was some underlying implementation issue that led to its
> >removal.
> 
> If I remember correctly, Sylvain started to make things work that he needed
> when porting the updated PPP sources. It doesn't necessarily mean there was
> an issue, but I guess he didn't want to implement proxy ARP support in the
> lwIP ARP layer unless he needed it...

Indeed. If it would be implemented proxy ARP control plane should live 
in the netif core code and data plane in the ARP layer. There is no ARP 
proxy support per se on the PPP protocol, PPP layer do no more than 
setting a few internal flags and asking the system to set/remove an ARP 
proxy entry.

Anyway, ARP proxies seem to be a mostly dead thing nowadays, and I 
consider that a good thing because it's a huge layer violation. However, 
if some day ARP proxy support materialize in the ARP layer I will of 
course make it works for PPP since it is just a couple of flags and 
functions calls.


Sylvain

signature.asc
Description: Digital signature