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Author Topic: Modem monitoring (again)  (Read 247 times)

Weaver

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  • Retd sw dev; A&A; 3 × 7km ADSL2; IPv6; Firebrick
Modem monitoring (again)
« on: January 13, 2018, 08:15:55 PM »

[warning : bad day today, now extremely heavily drugged up with new load of pain medication, so v fuzzy and. 😵 ]

I just an intriguing thought. Seeing as I happen to have a spare router, I have a spare Firebrick, an FB2500, I could perhaps put it to some good use. What if I plug a small switch into one of the modems? Then I run several further ethernet cables:

i. First cable goes from the new small switch back to the main Firebrick, to the WAN port that the modem is supposed to be connected to. That restores normal service from the modem.

ii. Second cable goes from the small switch to the secondary Firebrick.

iii. The secondary Firebrick now has a second cable to the main LAN large switch.

The secondary Firebrick picks up stuff from the modem and re-routes it, but also possibly uses its optional NAT rewriting abilities to change IPv4 addresses. It certainly can rewrite source addresses and ports but the worry is whether it can do the same for destination addresses. I could do with a little guidance here.

Between the secondary Firebrick and its modem let us use an IPv4 subnet of <whatever?>, perhaps an RFC1918 address range. We could perhaps just use the range that the modem defaults to for its IPv4 admin http interface. If I can get the Firebrick to receive incoming packets from the main LAN and route them to the modem, NAT'ing on the way, then a box on the main LAN could talk to the modem and monitor it.

Main LAN is a subnet that has a static public, globally-routable (non-rfc1918) ‘straight’ IPv4 /26, and for IPv6 it has a static, globally-routable, public /64.

I get the feeling that I’m being incredibly stupid here and all I'm really asking for is what a domestic CPE does anyway, with the modem being the ‘home LAN’ and my main LAN being the ‘internet’. Is that correct?

(Insanity check: I dont see the point of putting the modem into a /29 or smaller that lies inside the main LAN's /26 and getting the Firebrick to re-route from one port to another as I think ?I'm just going to confuse the Firebrick because of interfaces that have overlapping address ranges. I presume that would be madness?)

If I get this set up correctly, I could use the web admin i/f of the modem to see some numbers. I could perhaps telnet into it.

Wasn't there an extensive thread about exactly the latter done by one of our superb researcher kitizens some years back?

The Dlink DSL-320B-Z1 in question doesn't have Broadcom-type firmware in it, but I dimly remember that you can get the usual extensive range of stats out of the thing, albeit using commands that are perhaps somewhat differ [?] than those from the standard well-known Broadcom litany. But if memory serves our earlier researcher did a lot of work already in documenting them.

I don't have an existing library or software tool that I can use productively on the iPad that can speak telnet (nor even straight TCP). I have a Python development system for and interpreter for the iPad, but I have zero clue about Python and wouldn't know where to begin. I might be able to possibly find something from somewhere though. Shudders.

I could perhaps more likely write something for the Rasberry Pi if I ever get it going again, but I've never done any Linux C programming. I'm a big fan of the D language (a more advanced C++), I have two excellent D compilers, GDC (GCC family), LDC (LLVM family) and both produce superb code quality. Perhaps I can dig out some friendly networking library there.

But a box to talk to a modem and monitor it would be fun. I would need a UI of some sort.
« Last Edit: January 13, 2018, 08:30:56 PM by Weaver »
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burakkucat

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Re: Modem monitoring (again)
« Reply #1 on: January 13, 2018, 10:22:56 PM »

I can certainly "see" what you would like to do but I am not third generation Firebrick literate. (There is a second generation Watchfront Firebrick FB105 in "The Grotto", at the Cattery, for use on special occasions. (E.g. When performing a "cat-in-the-middle" traffic sniffing session, etc.))

When the Dlink DSL-320B-Z1 is configured as a bridge, what happens to the LAN ports? Are they all in parallel and equivalent? Or are all bar one disabled?

I can't put my paws on it at the moment but I am sure Chysalis has written a guide how to have both the Ethernet frames, from the bridge, and from modem status monitoring pass over the same Ethernet cable.
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Weaver

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Re: Modem monitoring (again)
« Reply #2 on: January 13, 2018, 11:24:24 PM »

I could do with some help digging out that encyclopaedic old thread about this model.

@Burakkucat, I can send you one of these modems to play with if you are interested? I'm sure I have lots of spares.

As far as I can see from squinting at an image of the back of what I think might be one of these models, dug up by google, it doesn't have any extra ethernet ports, so no built-in switch.

Does all that I am doing amount to inventing the exact equivalent of the ‘domestic’-type CPE then?
« Last Edit: January 13, 2018, 11:26:52 PM by Weaver »
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burakkucat

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Re: Modem monitoring (again)
« Reply #3 on: January 14, 2018, 12:12:42 AM »

I could do with some help digging out that encyclopaedic old thread about this model.

I'll try to see if I can find it . . . Did you contribute to the thread? If yes, then checking every one of your posts will eventually lead to it.

Quote
@Burakkucat, I can send you one of these modems to play with if you are interested? I'm sure I have lots of spares.

To be honest, I have too much "on the go" and don't feel that I could contribute much.

Quote
As far as I can see from squinting at an image of the back of what I think might be one of these models, dug up by google, it doesn't have any extra ethernet ports, so no built-in switch.

Ah, right. So it is of similar construction to the Huawei SmartAX MT882, of which I am familiar. In the case of the latter, when configured as a pure bridge and connected to my circuit, it acts as an ATM end-point and converts to/from G.992.3 from/to Ethernet frames. It has an IPv4 address in its own right. Both Ethernet frames appear at the solitary 8P8C socket and it depends upon which sort of device is there connected as to what can be done. I can attach a device acting as a local PPP client (I prefer to think of that abbreviation as Peer-to-Peer Protocol rather than Point-to-Point Protocol) and begin a session with the remote Juniper device or I can attach a device in the same sub-net as the MT882 and access its internals via the configuration interface.

Quote
Does all that I am doing amount to inventing the exact equivalent of the ‘domestic’-type CPE then?

Yes and no, would be my (Sir Humphrey-like) answer. Creation of a block diagram, with the various bits of gubbins annotated as to what's what, may help you to express exactly what you would like to do and may help others to offer viable suggestions.
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Weaver

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Re: Modem monitoring (again)
« Reply #4 on: January 14, 2018, 01:30:41 AM »

I found the thread thanks to Kitz's sophisticated search function
    http://forum.kitz.co.uk/index.php/topic,17065.0.html

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burakkucat

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Re: Modem monitoring (again)
« Reply #5 on: January 14, 2018, 02:39:28 PM »

I found the thread thanks to Kitz's sophisticated search function
    http://forum.kitz.co.uk/index.php/topic,17065.0.html

Excellent! That is one thing off my ever expanding ToDo list.  :)
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Weaver

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  • Retd sw dev; A&A; 3 × 7km ADSL2; IPv6; Firebrick
Re: Modem monitoring (again)
« Reply #6 on: January 16, 2018, 01:57:37 AM »

I now discover some guidance from the hero G.DMT at
    http://forum.kitz.co.uk/index.php?topic=17065.msg314522#msg314522
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burakkucat

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Re: Modem monitoring (again)
« Reply #7 on: January 16, 2018, 03:56:25 AM »

I now discover some guidance from the hero G.DMT at
    http://forum.kitz.co.uk/index.php?topic=17065.msg314522#msg314522


Ah, yes. I can see something there that could well assist you with your quest.  :)
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