[TriLUG] OT broadband question

Andrew Perrin clists at perrin.socsci.unc.edu
Wed Jan 15 14:28:28 EST 2003 

This may be their intention, but it is not always implemented. Note the
transcript below from my home computer, which is on an earthlink cable
setup:

aperrin at dhcp-1032-2404:~$ telnet smtp.unc.edu 25
Trying 152.2.1.243...
Connected to smtpsrv12.isis.unc.edu.
Escape character is '^]'.
220 smtp.unc.edu ESMTP Sendmail 8.12.2/8.12.2; Wed, 15 Jan 2003 14:27:06
-0500 (EST)
quit
221 2.0.0 smtp.unc.edu closing connection
Connection closed by foreign host.


ap

----------------------------------------------------------------------
Andrew J Perrin - http://www.unc.edu/~aperrin
Assistant Professor of Sociology, U of North Carolina, Chapel Hill
clists at perrin.socsci.unc.edu * andrew_perrin (at) unc.edu


On Wed, 15 Jan 2003, Ryan Leathers wrote:

> Yes Sir,
> 
> Earthlink's policy is to block port 25 for all dial, DSL, and cable
> customers.
> Mindspring used to do this and when Earthlink absorbed them a couple
> years ago they adopted the policy.
> The intent is to limit the spam that might otherwise originate from
> Earthlink customers.
> 
> Details on their policy may be found at
> http://help.earthlink.net/port25/
> Though some of the language on this page seems to indicate that this is
> only for dial users rest assured that the blocking is not transport
> technology dependant.  DSL and cable users will "benefit" just as much
> as dial users from this filtering.  The fact that Sprint is the DSL
> provider or that they do/do not use barbed wire to reach you makes no
> difference.  See my previous post regarding this point...
> 
> Ryan
> 
> 
> -----Original Message-----
> From: Robert Baker [mailto:rbaker at smithlaw.com]
> Sent: Wednesday, January 15, 2003 1:26 PM
> To: 'trilug at trilug.org'
> Subject: RE: [TriLUG] OT broadband question
> 
> 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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> >>TriLUG Organizational FAQ:
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> >>
> >>  
> >>
> >
> >_______________________________________________
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> >
> >
> >
> 
> 
> 
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