Re: [tlug] Problems with au ADSL/network setup

[Jens Oliver John <lists@example.com>]

(First post here, hello all.)

It seems very unlikely that the modem messes with the network behind the
router, because I assume that the modem is plugged into the router's WAN
port and the network is therefore NATed -> the router is the one which
does DHCP for the network Wifi and LAN? Any DHCP packets from the modem
should not find their way into the network behind the router.

The Wifi continues to work, which implies that connected clients still
use the router as the gateway and the router's DHCP works correctly in
the Wifi --- if the Wifi is being operated separately from the wired
network, then it seems plausible that one of your friend's devices in
the cable network is messing with the DHCP or spoofing ARP messages
which would need to get fixed. I would run wireshark and try to identify
misbehaving network clients.

If the Wifi is fully switched with the wired network, then I am at a
loss for explanation? Did you test the routers + modem combinations at
your friend's with the full LAN connected or with a minimal setup (just
modem + 1 router + 1 computer trying to access the admin interface)?

In any case I'd run wireshark and look what happens in the network. To
sniff between router and modem, insert an extra switch and sniff from
there?

Regards
Jens.

On Fri, Nov 22, 2013 at 09:17:26PM +0900, Stefan A. wrote:
> Hi all,
> 
> A friend of mine is having problems with his home internet connection
> and asked me for help, but I can't for the life of me figure out what
> is wrong and so I was hoping someone on here may be able to give advice.
> 
> The problem: My friend uses some older type of au ADSL with a modem
> which he rented from his provider. The modem only has one Ethernet LAN
> port and no wifi (au charges extra for wifi), so he connected an IOData
> WN-G54/R4 router to the modem a few years ago to share his connection
> between several local systems (by cable) and his smartphone/tablet
> (wifi). This worked well until a few months ago, when he couldn't reach
> his router's admin interface anymore. Suspecting that the router was at
> fault, which was by now pretty old and didn't support WPA2 anyway, I
> gave him a spare Buffalo WHR-G301N router. But after hooking it up to
> his modem, I was baffled to find that the same thing happened. The
> modem seems to overwrite the IP addresses allocated by the router(s)
> shortly after connecting them, making it impossible to reach the
> router's admin interface. Wifi is still working, but my friend reports
> that it breaks down occasionally, making a reboot of the (Buffalo)
> router necessary.
> 
> Although I played around with the modem and the routers for some time,
> I was unable to determine what was going on. Frankly, I am at a loss at
> how such a weird combination of problems can even occur, although
> hardware issues (or gremlins) may play a role here. I was about to
> recommend throwing out all that old garbage, upgrading to Hikari (since
> his connection is quite slow) and getting a new router from au,
> although that means they would charge him extra for wifi, which I find
> petty. What are your thoughts/recommendations?
> 
> Stefan
> -- 
> Stefan A. <stefan.a@example.com>
> 
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