[PLUG] Response to your DCANet DSL Problems - WAS: Puzzling networking problem

["Andy Smith" <ajs@dca.net>]

Hello,

I have read with interest your reports of problematic connectivity using
your DCANet DSL service.  My name is Andy Smith and I'm the senior
engineer at DCANet.  I've also been lurking around PLUG for quite a
while now.

I'm happy to offer some explanations as to how or why your routing
problems have persisted.  There are a number of possibilities when it
comes to ADSL.  Since this is the PLUG list I feel I can go into some
technical detail which you may find interesting.

Your DSL circuit is a Verizon ADSL circuit, which means Verizon provides
the loop, and they carry your traffic back over their ATM network to
DCANet's facility in Philadelphia.  For every central office that
services Verizon ADSL, there is an ATM PVC (VPI / VCI) built from that
CO to our ATM port (which in this case is OC-3).  Some central offices
have multiple PVC's depending on the DSL density, DSLAM configuration,
etc.  Whether you get the IP service from DCANet, Verizon, or some other
ISP, the basic Layer-2 ATM network is the same.

Sometimes in this whole process, and lately more frequently, Verizon
will re-provision which ATM PVC your particular traffic traverses.  This
happens with no warning to us or to anyone else.  The problem is that
our router has a route for your particular IP address pointed to the
specific ATM PVC that your ADSL modem lives on.  Usually the end user
just has to release / renew DHCP (or, reboot, which does the same
thing).  When the computer comes back up and requests the IP address via
DHCP, our router knows to install the /32 route pointed to the ATM PVC
from which the DHCP request arrived.  All is well.

Even though the IP address is assigned with DHCP, we still abide by our
long standing policy / feature of assigning static IP to end users.  So
you'll get the same IP address every time from the DHCP server.  The
router will automatically install the route to the particular ATM PVC
you are on at the moment.  If you are interested, this feature of Cisco
IOS is called 'Route Bridge Encapsulation' (RBE).

I checked my router config, and your IP addresses have static routes
defined.  One way we could try and troubleshoot this for you would be to
remove these static routes, and have you switch to using DHCP for IP
acquisition.  This will solve the potential problem of Verizon changing
the ATM network on us, and will hopefully eliminate this as a possible
source of trouble.   Feel free to contact myself if you would like
assistance with this.

Finally I think it should be pointed out that Verizon ADSL is exactly
that -- Verizon ADSL.  It's the least-common-denominator broadband
service available.  Here at DCANet we try and make it a usable 'power
user' type service to appeal to the more tech savvy users, with static
IP, routed netblocks, no PPPoE, reverse DNS options, no port filtering,
no content monitoring, etc.  It's a raw and pure IP connection which is
the way Internet access was meant to be delivered.  Don't expect to do
anything mission critical on Verizon ADSL though.  It's not intended for
it, and it's not something that should be depended upon for highly
available service.  We do what we can on our side to make Verizon ADSL a
good product but at some point we're at the mercy of how Verizon runs
their own network.

If you need a circuit for critical services, or something that is more
stable and more reliable, we can certainly talk to you about loops from
Covad, AT&T, Worldcom, Verizon T1, etc.  The prices on traditional T1
circuits have really dropped in the last few years, to the point where
they may be acceptable to certain users.

Also I really have to take issue with you calling a member of my staff
'incompetent' or saying that they do not have an 'understanding of how
to solve problems' in a public forum.  We're all adults here.  I can
understand your frustration and I do hope that we can resolve your
issues to your satisfaction.  

Please let me know if I can be of assistance.  Thanks
 


Andrew Smith
Consult Dynamics / DCANet
215 440 1500 x153
302 654 1019 x107
 

___________________________________________________________________________
Philadelphia Linux Users Group         --        http://www.phillylinux.org
Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce
General Discussion  --   http://lists.phillylinux.org/mailman/listinfo/plug