[TriLUG] OT broadband question

Wed Jan 15 13:25:54 EST 2003

Ryan,

While waiting for Sprint, still waiting actually, to install my DSL service
I've been using Earthlink (dial-up) for about 4 months now.  Seems they
started blocking port 25 (smtp) unless your client was configured to use
their smtp server (smtp.earthlink.net).  I have my own domain at Intermedia
and use the pop/smtp servers on the domain, which is Intermedia's mail
server.  It took me hours to figure this out as I've never heard of a MAJOR
ISP blocking that port (though I have seen smaller ones do it.). I guess the
thought of Earthlink blocking that port never crossed my mind during trouble
shooting.

I wonder if Earthlink will do the same when I get my DSL from Sprint as
Earthlink provides the Internet access for all Sprint DSL subscribers?

Thanks

>>> Rob Baker <<<
Webcentric Applications Developer

-----Original Message-----
From: Ryan Leathers [mailto:Ryan.Leathers at globalknowledge.com] 
Sent: Wednesday, January 15, 2003 11:25 AM
To: 'trilug at trilug.org'
Subject: RE: [TriLUG] OT broadband question

In a nutshell the rest of this post says "No DSL providers filter stuff by
IP address or port number"

I have provided technical consulting to several DSL hardware vendors and
service providers - and am feeling unexplainably enthusiastic over this
topic this morning.  This entire discussion gets a bit cloudy inasmuch as a
DSL provider may also be an ISP and vice versa.  For purposes of clarity I
discuss them as separate entities.  

To my knowledge, no DSL service providers make forwarding decisions on
anything but layer2 although certain hardware vendors (notably Cisco,
Paradyne) include the ability to do so at layer3 and to some extent at
layer4.  In simple terms DSL is a physical layer technology which delivers
some number of bits over copper wire.  It so happens that most often the
bits are organized as Ethernet frames and in many cases this
Ethernet frame encapsulates a PPP frame.   PPP provides for
authentication, and forwarding is sometimes based on this prior to frame
delivery to an ISP POP (Redback or Shasta for example).  Whether a dynamic
IP address is provided in response to a DHCP lease request over an Ethernet
frame or in response to a PPP authentication through PPPoE the DSL service
provider will probably not even see it let alone make forwarding decisions
on it.  Instead, forwarding will be handled at layer2 in the DSLAM (or PPP
concentrator as described above) where either MAC or VCC addresses are
associated with customer ports (wire pairs).  Generally the DSLAM employs
some sort of MUX forwarding which eliminates the possibility of layer2
broadcast/discovery across its ports channeling everything through an uplink
interface.  This ensures that customers will be subject to whatever security
restrictions are imposed by the ISP.  The DSL modem (ATU-R) speaks Layer1 on
its provider interface and layer2 on its customer interface.  The modem
itself has no ability to filter.  An ISP may very well decide to filter
traffic (at their POP or upstream) based on port number or address, but
again, DSL has nothing to do with this so a change of ISP's might yield the
desired capabilities rather than a change of technologies.  In some cases an
ISP might provide a combination modem/router.  These can be managed remotely
and traffic can be filterd, shaped, etc., once again without the knowledge
of the DSL provider.  

It may also be interesting to note that while the Telecom standards bodies
were deliberating over DSL standards that would give them compatibility with
the Q.931 family of standards the Cable industry got together and whomped up
a broadband protocol that paid no heed to the Nx64 proponents.  Today,
DOCSIS supports QoS suitable for voice application and is every bit as
viable as the DSL protocols for residential applications.  DSL may yet
provide multi-line Nx64 over a single pair to business customers but the
CLECs who tried this a couple of years ago are all bankrupt now.  

Ryan 

-----Original Message-----
From: Chris Bullock [mailto:cgbullock at cox.net]
Sent: Wednesday, January 15, 2003 8:40 AM
To: trilug at trilug.org
Subject: [TriLUG] OT broadband question

Ben Pitzer wrote:

>DSL or cable?  Very important distinction in this instance.
>
Cable through cox communications.
--cgb

>
>Regards,
>Ben Pitzer
>
>---------------------------------------------
>
>"Those that can give up essential liberty to obtain a little temporary
>safety  deserve neither liberty nor safety."  --Ben Franklin--
>
>
>
>
>
>
> 
>
>>-----Original Message-----
>>From: trilug-admin at trilug.org [mailto:trilug-admin at trilug.org]On
Behalf
>>Of Chris Bullock
>>Sent: Tuesday, January 14, 2003 6:32 PM
>>To: trilug at trilug.org
>>Subject: [TriLUG] OT broadband question
>>
>>
>>I know we have some broadband employees in the group so helpfully
>>someone can answer my question.  I wanted to set up a small 
>>mail/webserver at my house but my ISP blocks a lists of ports, 80 and 
>>25 being the key ones I need.  They claim that the ports are blocked 
>>at the modem not at the routers.  How is this?  Does the modem receive 
>>a TFTP on the initial activation?  Just wanted to know for curiosity.
>>
>>thanks
>>
>>Chris
>>
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>>   
>>
>
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