Gentoo Archives: gentoo-user

From: Marc Joliet <marcec@×××.de>
To: gentoo-user@l.g.o
Subject: Re: [gentoo-user] Strange behaviour of dhcpcd
Date: Fri, 31 Oct 2014 14:53:03
Message-Id: 20141031155239.7f37fd3b@marcec.fritz.box
In Reply to: Re: [gentoo-user] Strange behaviour of dhcpcd by Rich Freeman
1 Am Fri, 31 Oct 2014 07:09:08 -0400
2 schrieb Rich Freeman <rich0@g.o>:
3
4 > On Fri, Oct 31, 2014 at 6:47 AM, Marc Joliet <marcec@×××.de> wrote:
5 > > Am Fri, 31 Oct 2014 07:52:54 +0100
6 > > schrieb "J. Roeleveld" <joost@××××××××.org>:
7 > >> On Tuesday, October 28, 2014 07:31:56 PM Marc Joliet wrote:
8 > >> >
9 > >> > - I don't know whether we have an IP block or not; I suspect not. At the
10 > >> > very least, we didn't make special arrangements to try and get one.
11 > >>
12 > >> Then assume not. Most, if not all, ISPs charge extra for this. (If they even
13 > >> offer it)
14 > >
15 > > That's what I thought :) .
16 > >
17 >
18 > Generally speaking you can't just attach a modem to your LAN and have
19 > it act as a DHCP server. Your ISP probably will assign you dynamic
20 > IPs, but they will not as a matter of policy assign you more than one
21 > unless you pay for them. IPv4 address space is in short supply these
22 > days.
23 >
24 > I'm using FIOS and in my case the "modem" is in a box in the basement
25 > and the ISP provides a router with the service. Whatever you plug
26 > into the "modem" will obtain a DHCP lease for one routable IP. If you
27 > do plug more than one device into the "modem" then the first device to
28 > get the IP is the only one that will get an IP - the modem won't hand
29 > out another unless it gets a DHCPRelease from the MAC that was issued
30 > the original lease or until that lease expires, or until you call up
31 > the ISP on the phone and get them to release it manually.
32 >
33 > Another design would be to issue a new IP anytime a device asks for
34 > one, but to silently cancel the lease of the last IP that was issued
35 > and drop packets using it. For a single device being plugged in that
36 > won't have any impact, and if for some reason you buy a new router and
37 > plug it in you don't have to worry about your old router still having
38 > a lease. This is less standards-compliant, but perhaps more
39 > clueless-friendly.
40 >
41 > In general, though, you really shouldn't be plugging your ISP's modem
42 > into anything but a router for general use. In fact, I have the
43 > router provided by my ISP configured as a bridge and running into
44 > another router (FIOS uses MoCA over coax in the standard install and
45 > I'm too lazy to run CatV and beg Verizon to reconfigure the modem to
46 > use the RJ45 connection instead). Note that if you use an
47 > ISP-provided router there is a good chance that they can essentially
48 > VPN into your LAN. The last time I called up Verizon over a cablecard
49 > issue they helpfully turned on DHCP on my router so that it started
50 > competing with my DHCP server, and then I was wondering why PXE was
51 > randomly failing. Now all they can do is disable bridge mode, which
52 > will break my external connection and be a fairly obvious point to
53 > troubleshoot.
54
55 Right, thanks for the explanation :) .
56
57 Thankfully, our ISP only gave us the modem (though they also offer modems with
58 WLAN for 5€ a monthg :-/ ). The router we bought off eBay ourselves :) .
59
60 --
61 Marc Joliet
62 --
63 "People who think they know everything really annoy those of us who know we
64 don't" - Bjarne Stroustrup

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