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Author Topic: Admin access to modems - second cable?  (Read 1362 times)

Weaver

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  • Retd s/w dev; A&A; 4x7km ADSL2 lines; Firebrick
Admin access to modems - second cable?
« on: September 17, 2018, 04:33:24 AM »
In order to get access to the admin UID of my modems I am wondering if I could simply run a second ethernet cable from each one to my main LAN switch. That is provided they have several ethernet interfaces on them and they all do the right thing.

Is that possible?

I would have to sort out the admin i/f IP addresses so that they do not clash, by reconfiguring the modems. At the moment they’re all identical, and are not in the LAN range.

If I can do that then I do not need to sort out the problem of access through the Firebrick nor pollute its configuration with a whole load of unnecessary complexity.
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j0hn

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Re: Admin access to modems - second cable?
« Reply #1 on: September 17, 2018, 08:48:40 AM »
Yes that is possible but it is entirely unnecessary.

With the correct config on your Firebrick you can access each individual modem through its existing single LAN cable.
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Ixel

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Re: Admin access to modems - second cable?
« Reply #2 on: September 17, 2018, 03:00:56 PM »
I did something like this with my DrayTek devices. However, the DrayTek devices also ended up broadcasting PPPoE connection attempts for some reason so I had to isolate the 'second cable' on each of them using a VLAN tag on my EdgeSwitch. Now they can no longer see each other, just the FireBrick, EdgeSwitch and my virtual machine which monitors and records DSL statistics from both of the DrayTek devices.
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Weaver

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  • Posts: 11459
  • Retd s/w dev; A&A; 4x7km ADSL2 lines; Firebrick
Re: Admin access to modems - second cable?
« Reply #3 on: September 17, 2018, 03:18:19 PM »
@Ixel - I was concerned about broadcast frames. I need to refresh on PPPoE. I would have thought the router sends out a PADI packet via an Ethernet broadcast which is essentially aimed at the modem, but I don’t see why there should be a broadcast coming out of the modem and thus getting into my main LAN and polluting it. Any thoughts?
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johnson

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Re: Admin access to modems - second cable?
« Reply #4 on: September 18, 2018, 12:57:30 AM »
A 2 cable solution, i.e 1 for the PPPoE session and 1 for admin/stats access works fine with zyxel modems, but you need to set up separate "Interface Groups" from the web gui as per:

https://kitz.co.uk/routers/zyxel_VMG8324-B10A_bridge.htm

Otherwise as Ixel mentioned, the modem is expecting to negotiate a PPPoE session over any cable plugged in. Each of these groups are assigned a different IP address that you can change under the "Home Networking" tab.
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Weaver

  • Senior Kitizen
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  • Posts: 11459
  • Retd s/w dev; A&A; 4x7km ADSL2 lines; Firebrick
Re: Admin access to modems - second cable?
« Reply #5 on: September 18, 2018, 06:55:48 AM »
Well spotted, I had forgotten about that article.
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