Wireshark-users: Re: [Wireshark-users] Using Wireshark for a DSL "link no surf" problem
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From: "Frank Bulk" <frnkblk@xxxxxxxxx>
Date: Wed, 18 Jun 2014 23:03:05 -0500

Normally if a modem is in bridging mode it doesn’t hand out IP addresses.  Something is not right here.

 

If you were my customer we’d have a tech onsite to assist a long time ago.

 

Frank

 

From: wireshark-users-bounces@xxxxxxxxxxxxx [mailto:wireshark-users-bounces@xxxxxxxxxxxxx] On Behalf Of Kok-Yong Tan
Sent: Wednesday, June 18, 2014 4:41 PM
To: Community support list for Wireshark
Subject: Re: [Wireshark-users] Using Wireshark for a DSL "link no surf" problem

 

Hmm…you've got a point.   I'll give it a shot when I get back. 

 

I've found that if I configure my firewall to ask for an IP, I get an IP in the private subnet of 192.168.1.0/24 and I've discovered that this is the out-of-band management subnet.  It then allows me to tap into the DSL modem at 192.168.1.1.   I also tried to do this by disconnecting my firewall from the DSL modem and then attaching my laptop directly to the DSL modem.  This is confirmed by a Tier 2 tech support rep at the ISP.  I get no IP in the public subnet. 

-- 

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On Jun 18, 2014, at 14:31 , Pedro Tumusok <pedro.tumusok@xxxxxxxxx> wrote:



You said your modem is in bridge mode, so any traffic arriving on the WAN port should be forwarded out the LAN port, so just do it on that. If you see any L2 data ie arp etc then the PVC are correct.

 

Have you tried configuring your firewall to ask for an IP instead of a static setup.

 

Pedro

 

On Wed, Jun 18, 2014 at 11:21 PM, Kok-Yong Tan <ktan@xxxxxxxxxxxxxxxxxxx> wrote:

Okay. Then my DSLAM interface is definitely up because I've got a solid (non blinking) green light on the LED for the DSL connection.  

 

Problem is: How to do a packet capture since I can only access traffic off the ethernet (RJ45) port and not the DSL (RJ11/RJ14) port?

 

-- 

Reality Artisans, Inc.              #   Network Wrangling and Delousing
P.O. Box 565, Gracie Station        #   Apple Certified Consultant
New York, NY 10028-0019            #   Apple Consultants Network member
<http://www.realityartisans.com> #   Apple Developer Connection member

 

On Jun 18, 2014, at 14:12 , Pedro Tumusok <pedro.tumusok@xxxxxxxxx> wrote:



If the DSL Led is on, on your modem, the DSLAM interface is up.

If the PVC is changed, then you should not see any L2 data, do a packet capture and see if you can see data coming from your modem.

 

Pedro

 

On Wed, Jun 18, 2014 at 8:58 PM, Kok-Yong Tan <ktan@xxxxxxxxxxxxxxxxxxx> wrote:

Yes, I understand why they gave me a /24 but with a /24, all it takes is for somebody else on the same subnet to accidentally (not intentionally or maliciously for obvious reasons) take my static IP and thus blow me out of the water without affecting them too much.  I had this happen once.  With a subnet between /24 and /30, they'd notice when their accidentally typo-ed IP address didn't work because it didn't match their gateway info.  

 

-- 

Reality Artisans, Inc.              #   Network Wrangling and Delousing
P.O. Box 565, Gracie Station        #   Apple Certified Consultant
New York, NY 10028-0019            #   Apple Consultants Network member
<http://www.realityartisans.com> #   Apple Developer Connection member

 

On Jun 18, 2014, at 10:59 , "Jamie O. Montgomery" <Jamie.Montgomery@xxxxxxxxxxxxx> wrote:



PPPoE is used for authentication. If you have a static IP, they know who has it and you don't need authentication. PPPoE would be the termination point for the address, but since it will reside on your firewall, the modem needs to bridge the dsl network to the Ethernet network on the public side if the firewall

 

They give you a /24 because they'd be burning up more IPv4 addresses giving you a smaller subnet. Other static IP customers use addresses in that subnet along with you. 

Jamie Montgomery | Comporium

Network Facilities Engineering | Engineering Associate II

www.comporium.com

jamie.montgomery@xxxxxxxxxxxxx



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On Jun 18, 2014, at 1:34 PM, "Kok-Yong Tan" <ktan@xxxxxxxxxxxxxxxxxxx> wrote:

No, the DSL modem is bridging, not routing.  I've been assigned two static IPs (although they've given me a /24 net mask!!!) and my firewall is assigned one of them.  The firewall is connected directly to the DSL modem by Cat6 patch cable.  The other IP is unused (I use it for testing VPN configurations).

 

I'm not sure but since the Broadxent Briteport is a PPPoE modem, I assume PPPoE.  But the tech says that's not correct (WTF?).  And he can't explain what they use.  Sigh.

-- 

Reality Artisans, Inc.              #   Network Wrangling and Delousing
P.O. Box 565, Gracie Station        #   Apple Certified Consultant
New York, NY 10028-0019            #   Apple Consultants Network member
<http://www.realityartisans.com> #   Apple Developer Connection member

 

On Jun 17, 2014, at 22:13 , Pedro Tumusok <pedro.tumusok@xxxxxxxxx> wrote:



Well if the tech can see stuff, its not what I thought might be the problem, which was PVC settings.

 

But does your modem get an IP address, ie is it setup as a router or does your computer get the ip address?

Are you using PPPoA/PPPoE etc?

 

On Wed, Jun 18, 2014 at 5:52 AM, Frank Bulk <frnkblk@xxxxxxxxx> wrote:

Some Comtrend modems can do a port mirror of the WAN (DSL) side.

Frank


-----Original Message-----
From: wireshark-users-bounces@xxxxxxxxxxxxx
[mailto:wireshark-users-bounces@xxxxxxxxxxxxx] On Behalf Of Kok-Yong Tan
Sent: Tuesday, June 17, 2014 4:53 PM
To: Community support list for Wireshark
Subject: Re: [Wireshark-users] Using Wireshark for a DSL "link no surf"
problem


> On Jun 17, 2014, at 14:28, Jaap Keuter <jaap.keuter@xxxxxxxxx> wrote:
>
>> On 06/17/2014 08:42 PM, Kok-Yong Tan wrote:
>> Is it possible to use Wireshark to troubleshoot a DSL "link no surf"
problem?  The ISP insists it's a CPE issue but the problem only started
after their Tier 1 tech monkeyed with the DSLAM and/or the CPE (remotely) in
some manner.  I find it suspicious that the problem was intermittent packet
loss until they tinkered, whereupon the problem became a "link no surf"
issue (i.e., there's Layer 2 connectivity but zero Layer 3 traffic passing).
>
> Depends on what you can trace in the CPE, as in, how close to the DSL
interface.
> Otherwise you'll need capture hardware on the DSL....
>
> Good luck,
> Jaap
>

I can get up to the DSL modem itself.  In hindsight, I'm thinking this isn't
going to be of much use and the only way to debug this is with capture
hardware on the DSL side as you suggested.  Drat.
--
Sent from my iPad2 with greater chance of typographical, grammatical and
other disasters.  Your indulgence is even more humbly requested.

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--
Best regards / Mvh
Jan Pedro Tumusok

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--
Best regards / Mvh
Jan Pedro Tumusok

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--
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Jan Pedro Tumusok

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