On 2016/06/08 09:54, Gerhard Roth wrote:
> On Tue, 7 Jun 2016 16:31:21 +0100 Stuart Henderson <[email protected]>
> wrote:
> > On 2016/06/07 14:39, Gerhard Roth wrote:
> > > > > Now I get an IP address from my provider, I want something like this:
> > > > >
> > > > > inet 10.75.178.41 --> 10.75.178.42 netmask 0xfffffffc
> > > > >
> > > > > But if I used SIOCAIFADDR I would get this instead:
> > > > >
> > > > > inet 0.0.0.1 --> 0.0.0.2 netmask 0xff000000
> > > > > inet 10.75.178.41 --> 10.75.178.42 netmask 0xfffffffc
> > > > >
> > > > > And deleting the old one first seems more racy.
> > > >
> > > > Why?
> > >
> > > Because either there is a time without any IP address or there
> > > is one with two addresses. Neither seems right.
> >
> > Is there a problem to have no address? That is what happens with
> > gif(4), tun(4) etc, even with ethernet interfaces, when they don't
> > have a particular address configured on them.
> >
> > There doesn't seem a particular problem with dhclient removing
> > the old address before it adds a new one..
> >
> > > See above. That's the current OpenBSD model for PPP.
> >
> > There are several models :-)
> >
> > The 0.0.0.1 thing is a specific hack for sppp/pppoe which has
> > "magic" values of 0.0.0.0 and 0.0.0.1 and a way to request a
> > specific hardcoded address. This is because *both* sides
> > propose addresses via IPCP (they are "equal" peers as far
> > as configuration is concerned), they have to agree and can
> > NAK each other.
> >
> > It's not the only way though, even for PPP; ppp(4) doesn't use
> > this mechanism, it has separate configuration for pppd instead.
> > When we had ppp(8), that didn't, either.
> >
> > As far as I understand MBIM addressing is driven from the "mobile
> > network" side, we just set the address they are telling us to use
> > without a way to propose our own address. If that's correct then
> > we don't need a way to set "our side's" address at all, or have
> > a way to tie down the remote side's address, so address
> > configuration can be a lot simpler than any PPP interface.
>
> I not sure if it is possible to send packets from an interface
> that has no addresses assigned to it.
Ah, I don't mean "no addresses assigned at all", I'm talking about
"deleting the old one first seems more racy" that you mentioned
in your mail.
I just mean it's ok to have no address temporarily - before you
connect to the network and have an assigned address, or when you're
regaining link or moving between networks and you remove the address
so you can add a new one.
Based on other interface types, how things work in non-OpenBSD routers,
etc, I'd expect it to work something like this:
interface attached ->
- no address
ifconfig up (IFF_UP) ->
- still no address (unless the user has manually set one)
- attempt connection
connection succeeds or regain link ->
- either: if no existing address, add it.
- or: if address matches one already configured, keep it.
- or: if address has changed, delete old address and add new.
- set IFF_RUNNING
lose link ->
- clear IFF_RUNNING (so no more packets will be sent over
interface) but keep address.
ifconfig down (IFF_DOWN) ->
- clear IFF_RUNNING and IFF_DOWN, keep address.
pppoe(4) is more complex because it has IFF_LINK1 aka IFF_AUTO
"dial-on-demand" behaviour which probably nobody uses, plus pppoe
is doing some things wrongly because I have observed cases where
it automatically moves between !IFF_UP and IFF_UP, this is
"administrative status" and meant to only be configured by the
admin, and also it sets IFF_RUNNING ("operational status") when
the link is not connected.
> > > > But when you lose the connection with the network or you manually set
> > > > the interface down, this IP address once given to you by the provider
> > > > is no longer yours and must not be used anymore.
> >
> > The same can apply in other cases (wifi, wired ethernet etc) too,
> > but we don't do anything to remove it from those interfaces (though
> > it's easy enough to remove using ifstated if needed).
>
> For WiFi and Ethernet it is dhclient that will remove the old
> addresses.
Yes, not when link is lost though, only once it has a new lease -
it maintains the old address until that point (with IFF_RUNNING
cleared, so you aren't sourcing traffic from it).
btw, I'm trying to get some hardware together to work on this,
I found a cheap enough card on ebay that looks like it should
work, now I just need to find pigtails and antennas that don't
cost more than the card (and hope I can find somewhere at home
with enough signal to test as I can't get that SIM registered
to my femtocell..)
