unbelievable network problem

I have a cable modem connection to the internet. I have a linksys router
which goes into the modem, and my pcs connected to the router. The router
gets the IP address through dhcp, always xx.yy.zz.226.

Lately, due to bad weather, there were some power outages at the ISP, and
the network went down. Since then, my connection drops every few hours or
so.

To rule out problems with the router, I plugged in my pc straight into the
modem. I configure eth0 with dhcp. Now I get xx.yy.zz.8. If I still try
the router I get the old xx.yy.zz.226. Don't know why I'm getting
different addresses, when the ISP knows me by the mac address of the cable
modem. Anyway...

Still the connection drops every few hours, and I noticed it always
happens when the ISP (or someone!) sends out arp packets (Who has ... tell ...).

If I /etc/rc.d/init.d/network restart, the connection comes back up, with
xx.yy.zz.8 (the same address that eth0 always gets through dhcp).

Then I thought, maybe someone else on the network claims they have
xx.yy.zz.8, so I said let's configure eth0 MANUALLY (not dhcp) with the
STATIC IP that the router always gets: xx.yy.zz.226.

And that works too!

Don't know how, or for how long. The only explanation I can think of is
that both xx.yy.zz.226 and xx.yy.zz.8 happened to be unassigned by the
dhcp server. However, when the ISP updates its arp tables, it seems that
someone else claims to have my ip, and I loose the connection.

Does anybody have any insight about what might be going on? I'm even
considering horror scenarios with hunt arp poisoning, but I suspect more
misconfiguration on the ISP side.

In article <(E-Mail Removed)>,
(E-Mail Removed) says...
>
>I have a cable modem connection to the internet. I have a linksys router
>which goes into the modem, and my pcs connected to the router. The router
>gets the IP address through dhcp, always xx.yy.zz.226.
>
>Lately, due to bad weather, there were some power outages at the ISP, and
>the network went down. Since then, my connection drops every few hours or
>so.
>
>To rule out problems with the router, I plugged in my pc straight into the
>modem. I configure eth0 with dhcp. Now I get xx.yy.zz.8. If I still try
>the router I get the old xx.yy.zz.226. Don't know why I'm getting
>different addresses, when the ISP knows me by the mac address of the cable
>modem. Anyway...
>
>Still the connection drops every few hours, and I noticed it always
>happens when the ISP (or someone!) sends out arp packets (Who has ... tell ...).
>
>If I /etc/rc.d/init.d/network restart, the connection comes back up, with
>xx.yy.zz.8 (the same address that eth0 always gets through dhcp).
>
>Then I thought, maybe someone else on the network claims they have
>xx.yy.zz.8, so I said let's configure eth0 MANUALLY (not dhcp) with the
>STATIC IP that the router always gets: xx.yy.zz.226.
>
>And that works too!
>
>Don't know how, or for how long. The only explanation I can think of is
>that both xx.yy.zz.226 and xx.yy.zz.8 happened to be unassigned by the
>dhcp server. However, when the ISP updates its arp tables, it seems that
>someone else claims to have my ip, and I loose the connection.
>
>Does anybody have any insight about what might be going on? I'm even
>considering horror scenarios with hunt arp poisoning, but I suspect more
>misconfiguration on the ISP side.
>
Hello from the Eighth Doctor
Look at it this way, depending on who your ISP is, ComCast, TWC, Cox, or really
any Cable TV service provider who thinks they can deliver I'net access via their
Cable TV lines, could be at fault.

So, who's your provider? Without knowing that, we can suppose anything.
---
Gregg drwho8 atsign att dot net
"This signature loves cats, the bigger the better."

On 2005-07-23, Amadeus W. M. <(E-Mail Removed)> wrote:
> To rule out problems with the router, I plugged in my pc straight into the
> modem. I configure eth0 with dhcp. Now I get xx.yy.zz.8. If I still try
> the router I get the old xx.yy.zz.226. Don't know why I'm getting
> different addresses

Maybe your cable modem remember the mac id of the router.

> dhcp server. However, when the ISP updates its arp tables, it seems that
> someone else claims to have my ip, and I loose the connection.

Then contact your ISP.

Davide

--
kill -9 them all, let reboot -rf now sort them out
--Peter Gutmann

Amadeus W. M. wrote:

> To rule out problems with the router, I plugged in my pc straight into the
> modem. I configure eth0 with dhcp. Now I get xx.yy.zz.8. If I still try
> the router I get the old xx.yy.zz.226. Don't know why I'm getting
> different addresses, when the ISP knows me by the mac address of the cable
> modem. Anyway...

The DHCP server is talking to your computer or router and not the cable
modem. If it sees a different MAC address, it will assign a different IP
address. To get the same address for both devices, clone the computer's
MAC address to the router.

When you say the connection drops, do you mean that eth0 no longer has an
address? Has been turned down? A bit better description would come in
handy.

On Sat, 23 Jul 2005 06:49:40 -0400, James Knott wrote:

> Amadeus W. M. wrote:
>
>> To rule out problems with the router, I plugged in my pc straight into the
>> modem. I configure eth0 with dhcp. Now I get xx.yy.zz.8. If I still try
>> the router I get the old xx.yy.zz.226. Don't know why I'm getting
>> different addresses, when the ISP knows me by the mac address of the cable
>> modem. Anyway...
>
> The DHCP server is talking to your computer or router and not the cable
> modem. If it sees a different MAC address, it will assign a different IP
> address. To get the same address for both devices, clone the computer's
> MAC address to the router.
>

So how come the connection works when I give my eth0 statically, the IP
address that the router normally gets through dhcp? Could it be that
since my router is out of the loop, its address remains unassigned, so I'm
free to use it on eth0?

> When you say the connection drops, do you mean that eth0 no longer has an
> address? Has been turned down? A bit better description would come in
> handy.

eth0 still has an ip address, but I get no answer when I try to connect
anywhere. As if the response packets to my IP are being routed to some
other IP.

Again, I assign eth0 a static ip (the one the router would get),
and I put the appropriate default gateway in the routing table. Of course,
things stay this way at my end, until I change them.

> Hello from the Eighth Doctor
> Look at it this way, depending on who your ISP is, ComCast, TWC, Cox, or really
> any Cable TV service provider who thinks they can deliver I'net access via their
> Cable TV lines, could be at fault.
>
> So, who's your provider? Without knowing that, we can suppose anything.
> ---

Millenium.

For the last few years I had ATT, SBC, Comcast, Qwest, Road Runner, and
now Millenium. Without a doubt, Millenium is the worst nightmare. Aside
from these problems that I'm having now, every time it rains, the modem
goes offline, so I get cut off from the ISP.

On Sat, 23 Jul 2005 08:13:09 +0200, Davide Bianchi wrote:

> On 2005-07-23, Amadeus W. M. <(E-Mail Removed)> wrote:
>> To rule out problems with the router, I plugged in my pc straight into the
>> modem. I configure eth0 with dhcp. Now I get xx.yy.zz.8. If I still try
>> the router I get the old xx.yy.zz.226. Don't know why I'm getting
>> different addresses
>
> Maybe your cable modem remember the mac id of the router.
>
>> dhcp server. However, when the ISP updates its arp tables, it seems that
>> someone else claims to have my ip, and I loose the connection.
>
> Then contact your ISP.
>
> Davide

You think I didn't? They're useless, they don't know anything beyond
unplug the modem, turn off the computer, and reboot.

On 2005-07-23, Amadeus W. M. <(E-Mail Removed)> wrote:
> You think I didn't? They're useless, they don't know anything beyond
> unplug the modem, turn off the computer, and reboot.

Look, as far as I can see from what you said, the problem is not on your
side. You've paid for a service, you should get the service. If your ISP
doesn't want to give the service terminate your contract and go to another
ISP more willing to give you what you want. When enough peoples vote with
their feet, the lusemonkey goes out of business and the world become a
better place.

Davide

--
Five is a sufficiently close approximation to infinity.
-- Robert Firth

Amadeus W. M. wrote:

>> Then contact your ISP.
>>
>> Davide
>
> You think I didn't? They're useless, they don't know anything beyond
> unplug the modem, turn off the computer, and reboot.

Next time, reboot the modem out the window. ;-)

Amadeus W. M. wrote:

> On Sat, 23 Jul 2005 06:49:40 -0400, James Knott wrote:
>
>> Amadeus W. M. wrote:
>>
>>> To rule out problems with the router, I plugged in my pc straight into
>>> the modem. I configure eth0 with dhcp. Now I get xx.yy.zz.8. If I still
>>> try the router I get the old xx.yy.zz.226. Don't know why I'm getting
>>> different addresses, when the ISP knows me by the mac address of the
>>> cable modem. Anyway...
>>
>> The DHCP server is talking to your computer or router and not the cable
>> modem. If it sees a different MAC address, it will assign a different IP
>> address. To get the same address for both devices, clone the computer's
>> MAC address to the router.
>>
>
> So how come the connection works when I give my eth0 statically, the IP
> address that the router normally gets through dhcp? Could it be that
> since my router is out of the loop, its address remains unassigned, so I'm
> free to use it on eth0?

You "own" the IP address for the duration of the DHCP lease. So, until the
lease has expired, there should be no one else using the address. However,
some systems might not like seeing a computer, with an unassigned address.

>
>> When you say the connection drops, do you mean that eth0 no longer has an
>> address? Has been turned down? A bit better description would come in
>> handy.
>
> eth0 still has an ip address, but I get no answer when I try to connect
> anywhere. As if the response packets to my IP are being routed to some
> other IP.

What happens if you ping the ISPs router? Watch what happens, using
something like Ethereal.

>
> Again, I assign eth0 a static ip (the one the router would get),
> and I put the appropriate default gateway in the routing table. Of course,
> things stay this way at my end, until I change them.

A few years ago, I had a similar problem, but sending out an occasional ping
cleared the problem, which I suspected was with their arp cache. If
pinging the router clears the problem, you might configure your system to
ping the ISPs router on a periodic basis.