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Laptop wireless - flaky at home, OK at office

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  Laptop wireless - flaky at home, OK at office "Charlie Gibbs" <cgibbs@kltpzyxm.invalid> - 2014-03-02 18:48 -0800
    Re: Laptop wireless - flaky at home, OK at office Moe Trin <ibuprofin@painkiller.example.tld.invalid> - 2014-03-03 03:53 +0000
      Re: Laptop wireless - flaky at home, OK at office "Charlie Gibbs" <cgibbs@kltpzyxm.invalid> - 2014-03-03 11:36 -0800
        Re: Laptop wireless - flaky at home, OK at office Moe Trin <ibuprofin@painkiller.example.tld.invalid> - 2014-03-04 19:45 +0000
          Re: Laptop wireless - flaky at home, OK at office "Charlie Gibbs" <cgibbs@kltpzyxm.invalid> - 2014-03-04 18:23 -0800

#2763 — Laptop wireless - flaky at home, OK at office

I have a laptop running CrunchBang Waldorf:

cjg@cjglap-crunchbang:~$ uname -a
Linux cjglap-crunchbang 3.2.0-4/amd64 #1 SMP Debian 3.2.46-1 x86_64 GNU/Linux

I've configured its wireless interface both at home and at the office.
I take the machine back and forth without re-booting - at home I close
the lid and the machine goes into hibernation, I go to the office, open
the lid, and it wakes up, finds the wireless access point, gets a new IP
address (192.168.1.xxx), finds the office router, and happily accesses
the Internet.  The reverse - going from office to home - doesn't work
so well.  The laptop wakes up, gets an IP address (192.168.0.xxx), and
seems to know that the router is at 192.168.0.1 - but it only works for
a while, if at all.  Taking wlan0 down and bringing it back up makes
it work for a while, then it stops.  If I plug in an Ethernet cable,
everything is happy.  More or less - pings to the Internet take 5
seconds each, and pings to machines on my LAN (including my WAP/router)
come back "Destination Host Unreachable", even if I specify an IP
address instead of a hostname.

The route command takes 10 seconds to come back with:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref   Use Iface
default         192.168.0.1     0.0.0.0         UG    0      0       0 eth0
192.168.0.0     *               255.255.255.0   U     0      0       0 wlan0
192.168.0.0     *               255.25.255.0    U     0      0       0 eth0

If I unplug the Ethernet cable, the route command returns "wlan0" under
the Iface column on the default line, and loses the last eth0 line.

The copy of Windows XP I have running under VirtualBox on my laptop
doesn't have any trouble accessing machines on my LAN - or the
Internet - as long as the Ethernet cable is connected.  My wife's
laptop, which runs Windows 7, can access my LAN wirelessly.

The wireless network at the office broadcasts its ESSID, while my
home network doesn't.  Could this make a difference?

There must be some sort of configuration problem in my laptop.
Any suggestions as to where to look?  Is there a good guide to
setting up wlreless networking, expecially for laptops that move
from one network to another?

Thanks for any pointers anyone can provide...

-- 
/~\  cgibbs@kltpzyxm.invalid (Charlie Gibbs)
\ /  I'm really at ac.dekanfrus if you read it the right way.
 X   Top-posted messages will probably be ignored.  See RFC1855.
/ \  HTML will DEFINITELY be ignored.  Join the ASCII ribbon campaign!

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#2764

On 02 Mar 14, in the Usenet newsgroup comp.os.linux.networking, in article
<2523.209T780T11284469@kltpzyxm.invalid>, Charlie Gibbs wrote:

>I have a laptop running CrunchBang Waldorf:

Not familiar with it

>The reverse - going from office to home - doesn't work so well.  The
>laptop wakes up, gets an IP address (192.168.0.xxx), and seems to
>know that the router is at 192.168.0.1 - but it only works for
>a while, if at all.  Taking wlan0 down and bringing it back up makes
>it work for a while, then it stops.  If I plug in an Ethernet cable,
>everything is happy.  More or less

Problem has existed for 20+ years, but people keep repeating it.

>The route command takes 10 seconds to come back with:

Try "/sbin/route -n" (telling it to not make a DNS lookup).  "ping"
also has a -n option.

>Kernel IP routing table
>Destination  Gateway      Genmask         Flags Metric Ref  Use Iface
>default      192.168.0.1  0.0.0.0         UG    0      0      0 eth0
>192.168.0.0  *            255.255.255.0   U     0      0      0 wlan0
>192.168.0.0  *            255.25.255.0    U     0      0      0 eth0

So, is 192.168.0.x on eth0 or wlan0.   ONE, NOT BOTH.  When the kernel
sees two routes to the same destination, it chooses the one that was
declared last, because it assumes you screwed up making the first
declaration, and the second one is the correction.   You can prove
this by running a packet sniffer on each interface, and seeing which
one is getting which packets.

Solution:  change wlan0 _OR_ eth0 to some other address range.  Or
simply don't use two interfaces.

        Old guy

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#2765

In article <slrnlh7v58.aq6.ibuprofin@fermi.phx.az.us>,
ibuprofin@painkiller.example.tld.invalid (Moe Trin) writes:

> On 02 Mar 14, in the Usenet newsgroup comp.os.linux.networking, in
> article <2523.209T780T11284469@kltpzyxm.invalid>, Charlie Gibbs wrote:
>
>> I have a laptop running CrunchBang Waldorf:
>
> Not familiar with it

It's a lean distribution built on Debian.

> So, is 192.168.0.x on eth0 or wlan0.   ONE, NOT BOTH.

But it is both - eth0 gets 192.168.0.24, wlan0 gets 192.168.0.23.

> When the kernel sees two routes to the same destination, it chooses
> the one that was declared last, because it assumes you screwed up
> making the first declaration, and the second one is the correction.
> You can prove this by running a packet sniffer on each interface,
> and seeing which one is getting which packets.

Yup, eth0 was getting all the packets.

> Solution:  change wlan0 _OR_ eth0 to some other address range.
> Or simply don't use two interfaces.

cjg@cjglap-crunchbang:$ sudo ifconfig eth0 down

Presto!

As for why it worked at the office, I never bothered plugging in an
Ethernet cable there, and wlan0 picked up an address of 192.168.1.xxx
instead of 192.168.0.xxx, so there was no conflict.

Thanks for the help.  I was primarily using the wired connection to
my laptop at home because I haven't been able to get VirtualBox to
bridge to a wireless connection, and I need my laptop to have access
to machines on my LAN as well as to the Internet, both natively and
through the virtual WinXP machine.  Unfortunately, this means that
I get wireless access to my LAN from the Linux host at the cost of
any network access from the virtual machine.

It could be worse, I suppose.  The WinXP VM is for work, so if I
want to use it I'll go into my home office, plug in the Ethernet
cable, bring up eth0, and do work.  If I want to play somewhere
else in the house, I'll unplug the cable, set eth0 down, and
have full wireless access from the Linux side.  It beats borrowing
my wife's laptop, which is a singularly unpleasant experience
seeing as it runs Windows 7 and has a really crappy keyboard.

-- 
/~\  cgibbs@kltpzyxm.invalid (Charlie Gibbs)
\ /  I'm really at ac.dekanfrus if you read it the right way.
 X   Top-posted messages will probably be ignored.  See RFC1855.
/ \  HTML will DEFINITELY be ignored.  Join the ASCII ribbon campaign!

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#2766

On 03 Mar 14, in the Usenet newsgroup comp.os.linux.networking, in article
<2365.210T2464T6965521@kltpzyxm.invalid>, Charlie Gibbs wrote:

>ibuprofin@painkiller.example.tld.invalid (Moe Trin) writes:

>> Charlie Gibbs wrote:

>>> I have a laptop running CrunchBang Waldorf:

>> Not familiar with it

>It's a lean distribution built on Debian.

About a month ago, Distrowatch.com reported

   DistroWatch database summary
     * Number of all distributions in the database: 768
     * Number of active distributions in the database: 290
     * Number of dormant distributions: 58
     * Number of discontinued distributions: 420
     * Number of distributions on the waiting list: 348

I simply don't try to keep track of them all.

>> So, is 192.168.0.x on eth0 or wlan0.   ONE, NOT BOTH.

>But it is both - eth0 gets 192.168.0.24, wlan0 gets 192.168.0.23.

Therein lies the problem. By default, the interfaces will each get a
"network route" for what is thought to be connected. Your tool[s]
brought up 192.168.0.24 as a /24 (255.255.255.0 mask), so everything
with a 192.168.0.xxx address is assumed to be connected/reachable via
that interface.  Another tool brought up 192.168.0.23. and we have the
same assumption - 192.168.0.xxx address is assumed to be
connected/reachable via _that_ interface. Somebody must be wrong.  It's
possible to have identical routes on both interfaces, but that requires
a dynamic routing daemon such as "routed", "gated" or "zebra" on all
hosts to sort things out - severe pain in the neck to do so.

>Yup, eth0 was getting all the packets.

Is CrunchBang using a "let me do this for you" type of network tool
such as Network Manager?  They try to second guess, and often get it
wrong.  What is often missing from the tool is a "sanity checker".

>cjg@cjglap-crunchbang:$ sudo ifconfig eth0 down

>Presto!

Yup - that will do it.

>As for why it worked at the office, I never bothered plugging in an
>Ethernet cable there, and wlan0 picked up an address of 192.168.1.xxx
>instead of 192.168.0.xxx, so there was no conflict.

When IP was developed (early 1980), multiple interfaces on a computer
were quite rare. The networking code in Linux was based on that
assumption. It will work quite well with multiple interfaces, but it
takes a tiny bit more effort - a LOT more if the same network is on
both interfaces.  Dynamic addressing service (BOOTP, later replaced by
DHCP) was much later (1988) and provided as a means of sharing scarce
IP addresses among multiple hosts.  RFC1597 (from 1994, replaced by
RFC1918 in 1996) provided for "private" IP space, which eliminated the
scarcity, but microsoft took advantage of the dynamic configuration to
simplify setup for the average user (who couldn't spell "IP" if asked).

The simple minded solution is separate networks.   At home, my wired
network is 192.168.1.x, and the router to the world is at 192.168.1.1.
The wireless network is on 192.168.3.x, and only 192.168.3.10 has a
second network card for 192.168.1.x.  Hosts on the 192.168.3.x, network
use 192.168.3.10 as their route to the world. The second NIC on that
box is listed as the route to 192.168.3.x for those on the wired LAN.

Ethernet hosts
default      192.168.1.1    0.0.0.0        UG    0      0       0 eth0
192.168.1.0  0.0.0.0        255.255.255.0  U     0      0       0 eth0
192.168.3.0  192.168.1.10   255.255.255.0  UG    0      0       0 eth0

192.168.[13].10
default      192.168.1.1    0.0.0.0        UG    0      0       0 eth0
192.168.1.0  0.0.0.0        255.255.255.0  U     0      0       0 eth0
192.168.3.0  0.0.0.0        255.255.255.0  U     0      0       0 wlan0

Wireless hosts
default      192.168.3.10   0.0.0.0        UG    0      0       0 wlan0
192.168.3.0  0.0.0.0        255.255.255.0  U     0      0       0 wlan0

Thus, there is no confusion of how to get where.   The wireless hosts
know they can talk directly to each-other, and if they want to talk to
a wired host (or the world) they send packets to 192.168.3.10 which
is acting as a router and will forward them.  Ethernet hosts know about
the other wired systems, know to send packets to 193.168.1.10 (the other
side of 192.168.3.10) to be forwarded to the wireless systems, and
everything else goes to 192.168.1.1.

>It could be worse, I suppose.

Planing ahead is often easier  ;-)   Incidentally, the '-n' option to
ping and route is to stop them from trying to look up the hostnames
for _display_ purposes.

>The WinXP VM is for work, so if I want to use it I'll go into my home
>office, plug in the Ethernet cable, bring up eth0, and do work.  If I
>want to play somewhere else in the house, I'll unplug the cable, set
>eth0 down, and have full wireless access from the Linux side.

It's nice being retired - but I haven't used windows since about 1990.
Not knowing what you are trying to do network-wise, I can't say much,
but having wired and wireless networks separated might do the job for
you. In the example above, host .10 on both networks is the primary
file-server, and seeing as how it wasn't all _that_ busy, I added the
second interface, and let it do routing between the two networks as
well.  My Ethernet uses fixed addresses, and the router/file-server
also ran a DHCP server for the wireless side (but using fixed addresses
based on MAC addresses).  That way, the laptops were asking for a
dynamic address/setup - which allowed them to work at the local
hot-spots, and yet gave them "known" addresses when they were at home.

        Old guy

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#2767

In article <slrnlhcbau.kum.ibuprofin@fermi.phx.az.us>,
ibuprofin@painkiller.example.tld.invalid (Moe Trin) writes:

> On 03 Mar 14, in the Usenet newsgroup comp.os.linux.networking,
> in article <2365.210T2464T6965521@kltpzyxm.invalid>, Charlie Gibbs
> wrote:
>
>> cjg@cjglap-crunchbang:$ sudo ifconfig eth0 down
>>
>> Presto!
>
> Yup - that will do it.

<snip>

> The simple minded solution is separate networks.   At home, my wired
> network is 192.168.1.x, and the router to the world is at 192.168.1.1.
> The wireless network is on 192.168.3.x, and only 192.168.3.10 has a
> second network card for 192.168.1.x.  Hosts on the 192.168.3.x, network
> use 192.168.3.10 as their route to the world. The second NIC on that
> box is listed as the route to 192.168.3.x for those on the wired LAN.

I suspected that something like that might be the answer.  But it's
not really worth the effort to set up.  The only time I really need
to put the laptop's virtual machine on the network is when I back up
my main development box (another VM) - the laptop has compilers and
copies of my test beds so I can even do development on it as a
freestanding box, and copy everything back over at another time.
Meanwhile, the Linux side is fully operational wirelessly, so I
can wander around the house with it, and even ssh -X into my main
Linux box.

Thanks again for the help.

-- 
/~\  cgibbs@kltpzyxm.invalid (Charlie Gibbs)
\ /  I'm really at ac.dekanfrus if you read it the right way.
 X   Top-posted messages will probably be ignored.  See RFC1855.
/ \  HTML will DEFINITELY be ignored.  Join the ASCII ribbon campaign!

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