[AusNOG] Oddity

[Damian Guppy]

what happens when you unplug the cisco?

--Damian


On Fri, May 9, 2014 at 6:49 PM, Karl Auer <kauer at biplane.com.au> wrote:

> This is weird. Or at least, I think it's weird.
>
> Client has a phone tail (J11) coming into a little Netcomm NB6 ADSL2+
> router/modem. The Netcomm is on, and the ADSL light is lit up. The
> Netcomm is not attached by any means to anything else (and is not a
> wireless router). Specifically, there is no Ethernet connection to the
> Netcomm. Just power and an RJ11.
>
> Client has another link to the Internet. I'm not sure what it is, but
> since he can definitely get to the Internet and the Netcomm is not
> locally networked with anything, it seems to me I can be reasonably sure
> it's not the Netcomm, right? Hm. Read on.
>
> There's a Cisco 800 series router sitting there too; it's showing DSL
> "CD" on, and RX/TX is showing lots of activity. Another RJ11 tail runs
> into the Cisco, and this has an old piece of cardboard tied to it saying
> "New ADSL connection" and a phone number (yes - THAT sort of client).
> I'm guessing that's the Internet connection, but it's only a guess. It
> can't be the Netcomm, so it must be the Cisco, right?
>
> Well, maybe not. The client has a symmetrical DSL link from Telstra to
> an office in another town. Maybe the Cisco is handling that? In which
> case what's handling the Internet connection?
>
> Anyway, none of that is weird, that's just general ignorance. No; what's
> weird is that if I turn off the Netcomm, the client loses Internet
> connectivity. The Cisco's CD light stays on.
>
> About the only explanation I can think of is that somehow the external
> IP address of the Netcomm is involved in routing traffic to the client.
> I can't imagine how, though. I just can't believe that the Netcomm IS
> the Internet connection - with no Ethernet connected, no PPP light
> showing and (obviously) no Ethernet activity.
>
> I'm not seeking help here, I'm just fascinated by the fact that this
> Netcomm, not networked locally at all, can somehow affect the local
> network's Internet connectivity on (presumably) a completely other ADSL
> link. I didn't think that was possible, but clearly it is.
>
> Obviously I'm about to learn something :-)
>
> Regards, K.
>
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Karl Auer (kauer at biplane.com.au)
> http://www.biplane.com.au/kauer
> http://twitter.com/kauer389
>
> GPG fingerprint: EC67 61E2 C2F6 EB55 884B E129 072B 0AF0 72AA 9882
> Old fingerprint: B862 FB15 FE96 4961 BC62 1A40 6239 1208 9865 5F9A
>
>
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