[clue-tech] DSL providers

[Nate Duehr]

On 2/15/07, William <wwcluetech1 at kimballstuff.com> wrote:

> Qwest is the "line" provider, representing the "physical link layer" of
> the network protocol.  Run a traceroute outside your LAN to see for
> yourself that Qwest is not routing TCP/UDP traffic.  The first hop
> outside your LAN is *not* a Qwest router [unless Qwest is *also* your
> ISP].  For example, I use FRII DSL with Qwest as my line provider.
> After passing through my firewall, then my perimeter router, my "first
> hop outside my LAN" is FRII's DSL consumer gateway -- I never see any
> Qwest hops [unless I happen to be running a traceroute into Qwest's
> network on purpose, but that puts Qwest's routers at the end of the
> route, not the start].

Welllllll... not to belabor this TOO much, because it doesn't matter -- but...

Qwest *is* actually providing routing -- and there's plenty of routers
involved between your DSL connection and FRII... you just can't SEE
them because you're on what's called a "Virtual Private Connection"
over ATM.

>From the standpoint of your IP connection, it's transparent to the end
points, other than the PPPoA configuration and login information...
and the PPPoA is just going all the way to FRII to authenticate.  But
in-between there definitely are *routers*... but they're not routing
IP... at least not from what you can see, anyway...

The traffic going from the DSLAM  to FRII is routed via Qwest's ATM
cloud...  :-)

When they provision your circuit, that's why they need to know the
"ISP"... they have to nail up the end-points of the ATM connection to
you and your provider.  When they aren't told a provider, they nail
that end point up to their own routers... MSN and/or their own core.

> To illustrate with an alternative example:  When we all used dial-up
> modems, we didn't think of our telephone company as our ISP.  The
> twisted-pair copper line was just the physical link between us and our ISP.

Agreed.  The ISP is the company that provides you access to the
Internet backbone via IP.

[Another interesting side-note to this is that the MTU of a PPPoA
connection isn't big enough to hold a full 1500 MTU Ethernet frame.
It fragments.  You can often help your through-put on Qwest DSL by
setting your MTU's appropriately for the lowest-common-denominator
transport -- in this case PPPoA -- so you're not fragmenting every
packet that has a full payload at the DSL "modem".]

Nate