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 10:48:31
In Reply to: Re: [gentoo-user] Strange behaviour of dhcpcd by "J. Roeleveld"
1 Am Fri, 31 Oct 2014 07:52:54 +0100
2 schrieb "J. Roeleveld" <joost@××××××××.org>:
4 > On Tuesday, October 28, 2014 07:31:56 PM Marc Joliet wrote:
5 [...]
6 > > Oh, and there are two powerline/dLAN adapters in between (the modem is in
7 > > the room next door), but direct connections between my computer and my
8 > > brother's always worked, and they've been reliable in general, so I assume
9 > > that they're irrelevant here.
10 >
11 > Uh-oh... If you have multiple machines that can ask for a DHCP-lease, you
12 > might keep getting a different result each time it tries to refresh.
14 How so? You mean if the modem is directly connected to the powerline adapter?
15 I would be surprised if this were a problem in general, since AFAIU they're
16 ultimately just bridges as far as the network is concerned, not to mention
17 that they explicitly target home networks with multiple devices.
19 But in the end, it doesn't matter, since it's just for my desktop (which
20 doesn't have WLAN built-in); all other clients connect via WLAN.
22 FWIW, I chose poewrline because it seemed like a better (and driverless!)
23 alternative to getting a WLAN USB-stick (or PCI(e) card), and so far I'm quite
24 happy with it.
26 > > Furthermore, I found out the hard way that you *sometimes* need to reboot
27 > > the modem when connect a different client for the new client to get a
28 > > response from the DHCP server (I discovered this after wasting half a day
29 > > trying to get our router to work, it would log timeouts during
30 > > DHCPDISCOVER). I didn't think it was the modem because when we first got
31 > > it, I could switch cables around between my computer and my brother's and
32 > > they would get their IP addresses without trouble. *sigh*
33 >
34 > That's a common flaw. These modems are designed with the idea that people only
35 > have 1 computer. Or at the very least put a router between the modem and
36 > whatever else they have.
37 > Please note, there is NO firewall on these modems and your machine is fully
38 > exposed to the internet. Unless you have your machine secured and all unused
39 > services disabled, you might as well assume your machine compromised.
41 Yes, I wasn't explicitly aware of this, but it makes sense, since AFAIU the
42 modem's job boils down to carrying the signal over the cable network and
43 (on a higher level) dialing in to the ISP and forwarding packets. I would not
44 really expect a firewall there.
46 > I once connected a fresh install directly to the modem. Only took 20 seconds
47 > to get owned. (This was about 9 years ago and Bind was running)
49 Ouch.
51 I just hope the Fritz!Box firewall is configured correctly, especially since
52 there doesn't appear to be a UI for it. Well, OK, there is, but it's not very
53 informative in that it doesn't tell me what rules (other than manually entered
54 ones) are currently in effect; all it explicitly says is that it blocks NetBIOS
55 packets. The only other thing that's bothered me about the router is the
56 factory default (directly after flashing the firmware) of activating WPA2 *and*
57 WPA (why?!). I turned off WPA as soon as I noticed.
59 Out of curiosity, I looked through the exported configuration file (looks like
60 JSON), and found entries that look like firewall rules, but don't really know
61 how they apply. It's less the rules themselves, though, than the context, i.e.,
62 the rules are under "pppoefw" and "dslifaces", even though the router uses
63 neither PPPoE nor DSL (perhaps a sign that AVM's software grows just as
64 organically as everybody else's ;-) ). The one thing I'm most curious about is
65 what "lowinput", "highoutput", etc. mean, as Google only found me other people
66 asking the same question.
68 Anyway, it *looks* like it blocks everything from the internet by default
69 (except for "output-related" and "input-related", which I interpret to mean
70 responses to outgoing packets and... whatever "input-related" means), and the
71 manual seems to agree by implying that the firewall is for explicitly opening
72 ports. Also, I used the Heise "Netzwerk Check" and it reports no problems, so
73 I'm mostly relieved.
75 > > - At the time there was no router, just the modem. We now have a Fritz!Box
76 > > 3270 with the most recent firmware, but we got it after I "solved" this
77 > > problem.
78 > >
79 > > - I don't know whether we have an IP block or not; I suspect not. At the
80 > > very least, we didn't make special arrangements to try and get one.
81 >
82 > Then assume not. Most, if not all, ISPs charge extra for this. (If they even
83 > offer it)
85 That's what I thought :) .
87 Anyway, I think that I'll contact the dhcpcd maintainer (Roy Marples) directly
88 and ask for his opinion.
90 --
91 Marc Joliet
92 --
93 "People who think they know everything really annoy those of us who know we
94 don't" - Bjarne Stroustrup


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Subject Author
Re: [gentoo-user] Strange behaviour of dhcpcd Rich Freeman <rich0@g.o>
Re: [gentoo-user] Strange behaviour of dhcpcd "J. Roeleveld" <joost@××××××××.org>