Re: [gentoo-user] Strange behaviour of dhcpcd

[Marc Joliet <marcec@gmx.de>]

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Am Fri, 31 Oct 2014 07:09:08 -0400
schrieb Rich Freeman <rich0@gentoo.org>:

> On Fri, Oct 31, 2014 at 6:47 AM, Marc Joliet <marcec@gmx.de> wrote:
> > Am Fri, 31 Oct 2014 07:52:54 +0100
> > schrieb "J. Roeleveld" <joost@antarean.org>:
> >> On Tuesday, October 28, 2014 07:31:56 PM Marc Joliet wrote:
> >> >
> >> > - I don't know whether we have an IP block or not; I suspect not.  At the
> >> > very least, we didn't make special arrangements to try and get one.
> >>
> >> Then assume not. Most, if not all, ISPs charge extra for this. (If they even
> >> offer it)
> >
> > That's what I thought :) .
> >
> 
> Generally speaking you can't just attach a modem to your LAN and have
> it act as a DHCP server.  Your ISP probably will assign you dynamic
> IPs, but they will not as a matter of policy assign you more than one
> unless you pay for them.  IPv4 address space is in short supply these
> days.
> 
> I'm using FIOS and in my case the "modem" is in a box in the basement
> and the ISP provides a router with the service.  Whatever you plug
> into the "modem" will obtain a DHCP lease for one routable IP.  If you
> do plug more than one device into the "modem" then the first device to
> get the IP is the only one that will get an IP - the modem won't hand
> out another unless it gets a DHCPRelease from the MAC that was issued
> the original lease or until that lease expires, or until you call up
> the ISP on the phone and get them to release it manually.
> 
> Another design would be to issue a new IP anytime a device asks for
> one, but to silently cancel the lease of the last IP that was issued
> and drop packets using it.  For a single device being plugged in that
> won't have any impact, and if for some reason you buy a new router and
> plug it in you don't have to worry about your old router still having
> a lease.  This is less standards-compliant, but perhaps more
> clueless-friendly.
> 
> In general, though, you really shouldn't be plugging your ISP's modem
> into anything but a router for general use.  In fact, I have the
> router provided by my ISP configured as a bridge and running into
> another router (FIOS uses MoCA over coax in the standard install and
> I'm too lazy to run CatV and beg Verizon to reconfigure the modem to
> use the RJ45 connection instead).  Note that if you use an
> ISP-provided router there is a good chance that they can essentially
> VPN into your LAN.  The last time I called up Verizon over a cablecard
> issue they helpfully turned on DHCP on my router so that it started
> competing with my DHCP server, and then I was wondering why PXE was
> randomly failing.  Now all they can do is disable bridge mode, which
> will break my external connection and be a fairly obvious point to
> troubleshoot.

Right, thanks for the explanation :) .

Thankfully, our ISP only gave us the modem (though they also offer modems with
WLAN for 5€ a monthg :-/ ). The router we bought off eBay ourselves :) .

-- 
Marc Joliet
--
"People who think they know everything really annoy those of us who know we
don't" - Bjarne Stroustrup

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