Cable Modem Activity

Cable Modem Activity

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Subject Author Date
Cable Modem Activity Citizen Bob 08-09-2007
Posted by Citizen Bob on August 9, 2007, 10:47 pm
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What is causing thee activity on my cable modem when my computer is
not doing anything on the network.

The modem is connected to a Linksys router. In particular, the RCV
light is constantly blinking on the modem as is the ACT light on the
router. But the LINK/.ACT light on the router is not blinking. There
is no SEND activity.

What is sending those packets to my modem? Are they addressed only to
my IP address or are they part my Class C subnet from my ISP?


--

"Beer is proof that God loves us and wants us to be happy."
--Benjamin Franklin

Posted by Gene S. Berkowitz on August 9, 2007, 11:59 pm
says...
> What is causing thee activity on my cable modem when my computer is
> not doing anything on the network.
>
> The modem is connected to a Linksys router. In particular, the RCV
> light is constantly blinking on the modem as is the ACT light on the
> router. But the LINK/.ACT light on the router is not blinking. There
> is no SEND activity.
>
> What is sending those packets to my modem? Are they addressed only to
> my IP address or are they part my Class C subnet from my ISP?

The traffic you see are Address Resolution Protocol (ARP) packets.
They are used to find the hardware address that resolves to a particular
IP address. Extremely common, and harmless. Your router only passes
ARP requests within your sub-net.

--Gene

Posted by Tom Stiller on August 10, 2007, 7:20 am

> says...
> > What is causing thee activity on my cable modem when my computer is
> > not doing anything on the network.
> >
> > The modem is connected to a Linksys router. In particular, the RCV
> > light is constantly blinking on the modem as is the ACT light on the
> > router. But the LINK/.ACT light on the router is not blinking. There
> > is no SEND activity.
> >
> > What is sending those packets to my modem? Are they addressed only to
> > my IP address or are they part my Class C subnet from my ISP?
>
> The traffic you see are Address Resolution Protocol (ARP) packets.
> They are used to find the hardware address that resolves to a particular
> IP address. Extremely common, and harmless. Your router only passes
> ARP requests within your sub-net.
>

Or malware probes. My router logs between 1,000 and 2,500 bogus
connection attempts per day (about 90% for ports 1026, 1027, and 1028).
Multiply that by the number of subscribers on the loop and you have a
substantial load.

--
Tom Stiller

PGP fingerprint = 5108 DDB2 9761 EDE5 E7E3 7BDA 71ED 6496 99C0 C7CF

Posted by Citizen Bob on August 10, 2007, 7:29 am
On Fri, 10 Aug 2007 07:20:38 -0400, Tom Stiller

>> The traffic you see are Address Resolution Protocol (ARP) packets.
>> They are used to find the hardware address that resolves to a particular
>> IP address. Extremely common, and harmless. Your router only passes
>> ARP requests within your sub-net.

>Or malware probes. My router logs between 1,000 and 2,500 bogus
>connection attempts per day (about 90% for ports 1026, 1027, and 1028).

I have used WallWatcher with my Linksys and have also seen such
traffic.

>Multiply that by the number of subscribers on the loop and you have a
>substantial load.

My question is whether I am seeing traffic sent to my specific IP
address only or if I am seeing traffic that is sent to the whole
address range of the subnet I am on.

Your comment implies that my modem is seeing traffic that is sent to
the whole address range of the subnet I am on.


--

"Beer is proof that God loves us and wants us to be happy."
--Benjamin Franklin

Posted by Tom Stiller on August 10, 2007, 10:57 am
spam@uce.gov (Citizen Bob) wrote:

> On Fri, 10 Aug 2007 07:20:38 -0400, Tom Stiller
>
> >> The traffic you see are Address Resolution Protocol (ARP) packets.
> >> They are used to find the hardware address that resolves to a particular
> >> IP address. Extremely common, and harmless. Your router only passes
> >> ARP requests within your sub-net.
>
> >Or malware probes. My router logs between 1,000 and 2,500 bogus
> >connection attempts per day (about 90% for ports 1026, 1027, and 1028).
>
> I have used WallWatcher with my Linksys and have also seen such
> traffic.
>
> >Multiply that by the number of subscribers on the loop and you have a
> >substantial load.
>
> My question is whether I am seeing traffic sent to my specific IP
> address only or if I am seeing traffic that is sent to the whole
> address range of the subnet I am on.
>
> Your comment implies that my modem is seeing traffic that is sent to
> the whole address range of the subnet I am on.

I'm not sure how the provider distributes the traffic, but the cable is
a shared medium. The modem has to see all the traffic on its loop in
order to select and pass on that which is intended for a particular
subscriber.

--
Tom Stiller

PGP fingerprint = 5108 DDB2 9761 EDE5 E7E3 7BDA 71ED 6496 99C0 C7CF

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