Let's say that your ISP is company A. Then the packets leaving your router
pass through servers belonging to A. At some point you change your ISP to
company B. Then the packets will go through the servers belonging to B. Which
device(s) decide where to send the packets leaving your router and how does
it/they know to which provider to send them ? I understand that there are
probably many different set ups , I'm just asking for an idea how it might
work.

--
vlaho.ninja/prog

Spiros Bousbouras wrote:

> Let's say that your ISP is company A. Then the packets leaving your router
> pass through servers belonging to A. At some point you change your ISP to
> company B. Then the packets will go through the servers belonging to B.

For xDSL networks, your packets reach routers operated by A or B,
because your router authenticates and creates a PPP tunnel to A or B,
all traffic then travels through the tunnel.

</shortversion>

Andy Burns wrote:

> For xDSL networks, your packets reach routers operated by A or B,
> because your router authenticates and creates a PPP tunnel to A or B,
> all traffic then travels through the tunnel.

For ADSL the wiring will need to be changed in the exchange (aka central
office) to connect you to company B's equipment, for VDSL it's usually a
logical change, by the line provider to let you reach company B, rather
than a physical wiring change.

On Sun, 25 Jul 2021 10:52:07 +0100
Andy Burns <usenet@andyburns.uk> wrote:
> Spiros Bousbouras wrote:
>
> > Let's say that your ISP is company A. Then the packets leaving your router
> > pass through servers belonging to A. At some point you change your ISP to
> > company B. Then the packets will go through the servers belonging to B.
>
> For xDSL networks, your packets reach routers operated by A or B,
> because your router authenticates and creates a PPP tunnel to A or B,
> all traffic then travels through the tunnel.

How does my router know whether to communicate with the routers of A or B ?
How does it know their IP addresses for example ?

Regarding authentication , how does it know the right credentials ? For
example en.wikipedia.org/wiki/Challenge-Handshake_Authentication_Protocol
says
CHAP requires that both the client and server know the plaintext of the
secret, although it is never sent over the network.

So I guess that my router and the router of the ISP must know some common
secret. How does this get established ?

Spiros Bousbouras wrote:
> On Sun, 25 Jul 2021 10:52:07 +0100
> Andy Burns <usenet@andyburns.uk> wrote:
>> Spiros Bousbouras wrote:
>>
>>> Let's say that your ISP is company A. Then the packets leaving your router
>>> pass through servers belonging to A. At some point you change your ISP to
>>> company B. Then the packets will go through the servers belonging to B.
>>
>> For xDSL networks, your packets reach routers operated by A or B,
>> because your router authenticates and creates a PPP tunnel to A or B,
>> all traffic then travels through the tunnel.
>
> How does my router know whether to communicate with the routers of A or B ?
> How does it know their IP addresses for example ?

depends, you're not giving many clues in terms of which continent you're
on, or what connection type you have, these things do vary a bit.

If it's ADSL, your router hasn't got much choice, the wires from your
house lead straight to the equipment (DSLAM) for your ISP

> Regarding authentication , how does it know the right credentials ? For
> example en.wikipedia.org/wiki/Challenge-Handshake_Authentication_Protocol
> says
> CHAP requires that both the client and server know the plaintext of the
> secret, although it is never sent over the network.

In this country, only BT doesn't require authentication, because they
know which phone line you're on and use that instead

> So I guess that my router and the router of the ISP must know some common
> secret. How does this get established ?

all other ISPs either require you to put a username and password in
the router, or they pre-configure it before they send the router out to
you, or use an automatic configuration system TR-069 which uses an
identifier (e.g. serial number) of the router to setup the parameters
for you.

Spiros Bousbouras <spibou@gmail.com> wrote:
> On Sun, 25 Jul 2021 10:52:07 +0100
> Andy Burns <usenet@andyburns.uk> wrote:
>> Spiros Bousbouras wrote:
>>
>> > Let's say that your ISP is company A. Then the packets leaving
>> > your router pass through servers belonging to A. At some point
>> > you change your ISP to company B. Then the packets will go
>> > through the servers belonging to B.
>>
>> For xDSL networks, your packets reach routers operated by A or B,
>> because your router authenticates and creates a PPP tunnel to A or
>> B, all traffic then travels through the tunnel.
>
> How does my router know whether to communicate with the routers of A
> or B ? How does it know their IP addresses for example ?

You tell it via the "default route" you setup when you configure it.

On Sun, 25 Jul 2021 16:22:08 -0000 (UTC)
Rich <rich@example.invalid> wrote:
> Spiros Bousbouras <spibou@gmail.com> wrote:
> > On Sun, 25 Jul 2021 10:52:07 +0100
> > Andy Burns <usenet@andyburns.uk> wrote:
> >>
> >> For xDSL networks, your packets reach routers operated by A or B,
> >> because your router authenticates and creates a PPP tunnel to A or
> >> B, all traffic then travels through the tunnel.
> >
> > How does my router know whether to communicate with the routers of A
> > or B ? How does it know their IP addresses for example ?
>
> You tell it via the "default route" you setup when you configure it.

I never did any such configuring on my current router. But , since it was
provided by my ISP , it probably came preconfigured. But this leads to
another question : what if someone enters a route not for an ISP they are
subscribing to ? I'm guessing that some authentication will fail but if they
somehow manage to crack the authentication process then they can get internet
access without paying an ISP , right ? I was reading earlier
en.wikipedia.org/wiki/TR-069 and
www.pcworld.com/article/2463480/many-home-routers-supplied-by-isps-can-be-compromised-en-masse-researchers-say.html

and they say that routers are crackable. The setting is different but if an
outsider can crack a router then I'm guessing that the owner can too.

On 7/25/21 3:42 AM, Spiros Bousbouras wrote:
> Let's say that your ISP is company A. Then the packets leaving your
> router pass through servers belonging to A. At some point you change
> your ISP to company B. Then the packets will go through the servers
> belonging to B.

Please clarify the timing that you're talking about when you say "at
some point". Are you referring to a one time change - say ISP B is new
and offers a sale to get you to switch to them, or are you referring to
some special connection that uses both ISP A and ISP B /concurrently/
(depending on various configurations)?

The former is trivial and usually involves someone; ISP A, ISP B, or
common (telco) carrier C, making a change to ""re-wire your connection
from A to B.

The latter is possible, but usually is a much more complex configuration.

There is also an additional varient where you have two completely
independent connections, one to ISP A (xDSL) /and/ one to ISP B (DOCSIS).

> Which device(s) decide where to send the packets leaving your router
> and how does it/they know to which provider to send them ?

It depends.

> I understand that there are probably many different set ups , I'm
> just asking for an idea how it might work.

I hope the first scenario describes itself.

The second scenario depends on the access technology, how it's
configured, and what ISPs A and B support.

The third scenario is decided by your router picking which ISP
connection to use; A or B.

Please ask clarifying questions.

--
Grant. . . .
unix || die

On 7/25/21 3:57 AM, Andy Burns wrote:
> For ADSL the wiring will need to be changed in the exchange (aka central
> office) to connect you to company B's equipment, for VDSL it's usually a
> logical change, by the line provider to let you reach company B, rather
> than a physical wiring change.

That may be the case where you are. But where I'm from there is no
strict /need/ for any physical change.

Where I'm from the DSLAMs are almost always owned by the common carrier
telephone company (the Incumbent Local Exchange Carrier / ILEC). They
would logically change the configuration for a given line's DSLAM port
so that the connection changes from ISP A to ISP B. Quite like you're
alluding to with VDSL.

DOCSIS is a little bit different. Purportedly the DOCSIS /technology/
supports multiple ISP's sharing a head end and utilizing a common
outside plant Hybrid Fiber / Coax (HFC) network. However, I've never
heard of this being done in practice. This works quite similar to a
standard layer 2 switched Ethernet network. Each ISP simply looks like
a different Ethernet device across the DOCSIS / HFC network.

--
Grant. . . .
unix || die

On Sun, 25 Jul 2021 15:31:18 +0100
Andy Burns <usenet@andyburns.uk> wrote:
> Spiros Bousbouras wrote:
> > On Sun, 25 Jul 2021 10:52:07 +0100
> > Andy Burns <usenet@andyburns.uk> wrote:
> >> For xDSL networks, your packets reach routers operated by A or B,
> >> because your router authenticates and creates a PPP tunnel to A or B,
> >> all traffic then travels through the tunnel.
> >
> > How does my router know whether to communicate with the routers of A or B ?
> > How does it know their IP addresses for example ?
>
> depends, you're not giving many clues in terms of which continent you're
> on, or what connection type you have, these things do vary a bit.

I'm asking for my general education so any reply for any location and any
set up would be interesting to me.

> If it's ADSL, your router hasn't got much choice, the wires from your
> house lead straight to the equipment (DSLAM) for your ISP
>
> > Regarding authentication , how does it know the right credentials ? For
> > example en.wikipedia.org/wiki/Challenge-Handshake_Authentication_Protocol
> > says
> > CHAP requires that both the client and server know the plaintext of the
> > secret, although it is never sent over the network.
>
> In this country, only BT doesn't require authentication, because they
> know which phone line you're on and use that instead

Where "this country" means the U.K. So if it's an xDSL network then it is
physically possible for the packets to travel from any home router to several
ISPs. Who owns the routers which decide which ISP the packets go to ? Is
it BT ?

On Sun, 25 Jul 2021 12:23:56 -0600
Grant Taylor <gtaylor@tnetconsulting.net> wrote:
> On 7/25/21 3:42 AM, Spiros Bousbouras wrote:
> > Let's say that your ISP is company A. Then the packets leaving your
> > router pass through servers belonging to A. At some point you change
> > your ISP to company B. Then the packets will go through the servers
> > belonging to B.
>
> Please clarify the timing that you're talking about when you say "at
> some point". Are you referring to a one time change - say ISP B is new
> and offers a sale to get you to switch to them,

Yes , this is the scenario I was thinking but , as I've said in a different
post , I'm asking for my general education so hearing about other scenarios
is fine.

> or are you referring to
> some special connection that uses both ISP A and ISP B /concurrently/
> (depending on various configurations)?

On 7/25/21 8:31 AM, Andy Burns wrote:
> If it's ADSL, your router hasn't got much choice, the wires from your
> house lead straight to the equipment (DSLAM) for your ISP

ADSL in particular, and xDSL in general as I understand it, supports
common DSLAMs. (See my reply a few minutes ago for more details.)

ATM based DSL supports multiple PVCs across the single physical
connection. -- This would be called a Service Access Loop in ATM
parlance. -- Thus ATM based DSL /technically/ /supports/ concurrent
connections to multiple ISPs through the use of different PVCs.

I have used ATM DSL modems that supported up to eight different PVCs.
As in the modem itself established the PVC using the PVI and SVI
provided by the router.

> In this country, only BT doesn't require authentication, because they
> know which phone line you're on and use that instead

That's because there is association with the physical port on the DSLAM
with the phone line that is connected. This pre-defined circuit makes
it from the DSLAM through the provider's telco network to the router on
the far side. The router has different logical interfaces that
represent the physical DSLAM port. So there is a one-for-one mapping.
As long as the association / mapping is maintained properly, you can
easily know that logical port XYZ123 is phone number ABC-9876.

> all other ISPs either require you to put a username and password in the
> router, or they pre-configure it before they send the router out to you,

That may be the case where you are. But where I'm from, all three of
the ADSL ISPs (1 x ILEC and 2 x independent) used the one-for-one
mapping described above. The PPPoE / DHCP / static configuration is
actually (bridged / encapsulated) Ethernet frame riding across the DSL
network -- which is more akin to point-to-point logical Ethernet links
in this regard -- to the ISP who provides the counterpart for PPPoE /
DHCP / static configuration.

> or use an automatic configuration system TR-069 which uses an identifier
> (e.g. serial number) of the router to setup the parameters for you.

Things started with DHCP & static configuration and then progressed to
PPPoE where I'm from. The PPPoE enabled providers to care less (or not
at all) about the one-for-one mapping described above and instead rely
on PPPoE's authentication capabilities. Thus the DSL became even more
of a point-to-point Ethernet LAN. Or, more accurately point (ISP) to
multi-point (DSL subscribers) as subscriber to subscriber still needed
to pass through the ISP's head end, for both layer 2 and layer 3.

--
Grant. . . .
unix || die

On 7/25/21 12:30 PM, Spiros Bousbouras wrote:
> I'm asking for my general education so any reply for any location
> and any set up would be interesting to me.

That ask actually makes it harder to answer. That's sort of like asking
for a general description of how you get from New York to Los Angeles.
There are many different modes of travel; plain, train, automobile,
walking, boat, etc. Then there are many routes that could be used; east
to west (~direct), or east to west (indirect around the world).

Heck, there's even a chance that you could use a propulsion system to
jump almost straight up, slightly south trajectory, such that when you
came down the Earth would have rotated under you that you now land on
the west coast. The southerly trajectory is to account for the
latitudinal differences.

You *REALLY* do need to refine your question /some/ to get more
meaningful answers.

> So if it's an xDSL network then it is physically possible for the
> packets to travel from any home router to several ISPs.

Yes, it is (physically and logically) possible for a home router to send
packets to multiple ISPs /if/ the DSL network has been properly configured.

I'm wording this as if it's an ATM DSL connection, but the same concepts
exist with other types of DSL connections. Similar concepts also apply
to other types of connections.

Where I'm from, the ILEC owns the DSLAMs. So, ISP customers need their
phone line to be connected to a DSLAM. This is /usually/ requested by
the ISP, but I've heard of situations where the customer requests this
directly. The DSLAM is connected to the ATM network (think cloud). The
ISP is also connected to the ATM network. The ATM network owner
provisions a PVC from the DSLAM to the ISP for the given customer. Thus
when the ISP customer sends traffic, it goes over the DSL to the DSLAM,
through the ATM network to the ISP, and the ISP sees the traffic coming
in on the logical interface that represents the customer. The ISP then
routes the traffic through their IP network out to the Internet.

Aside: Depending on the size and / or complexity of the ISP's network,
there may be other networking technologies used between their ATM router
where DSL customer circuits terminate, through the ISP's core network,
out to the Internet.

There is no /technical/ reason why you can't have multiple PVCs from the
same DSLAM port that represents the subscriber's phone line, each going
to different ISPs. You could extend this to be two different PVCs to
the same ISP. Presumably, each PVC would terminate in different
locations. Though technically they could terminate in the same location
as separate virtual circuits for different types of traffic.

> Who owns the routers which decide which ISP the packets go to ? Is
> it BT ?

It depends.

You could make an argument that it's the DSLAM / ATM network owner's
equipment / configuration there of that decide which ISP the packets go to.

You could also make an argument that it's the customer's equipment that
picks the PVC (VPI & VCI) that traffic is sent down and that the DSLAM /
ATM network is simply passing things according to the PVC information.

Usually, there is only one PVC configured and the DSLAM / ATM network
operator is who decides how to ""route things.

Aside:
- The term "switching" is used at the ATM level in lieu of "routing".
- "Routing" is normally applied to IP packets at layer 3.
- The term "cell" is used at the ATM level in lieu of "packet".
- "Packets" usually refers to units of IP information at layer 3.

--
Grant. . . .
unix || die

Grant Taylor wrote:

> On 7/25/21 8:31 AM, Andy Burns wrote:
>> If it's ADSL, your router hasn't got much choice, the wires from your
>> house lead straight to the equipment (DSLAM) for your ISP
>
> ADSL in particular, and xDSL in general as I understand it, supports
> common DSLAMs.  (See my reply a few minutes ago for more details.)

For ADSL smaller ISPs here likely use BT's DSLAMs, larger ISPs have
provided their own, that's changing as more move to VDSL and use common
MSANs where the fibre backhaul reaches the street cabinet.

> ATM based DSL supports multiple PVCs across the single physical
> connection.

But do any providers make use of that? Technically it's possible but
here it's never used. It might have been nice to provision a home ISP
and a work ISP on the same line using different VCI/VPI numbers, most
providers used the same VCI/VPI nunbers, I can only think of one that
even used different numbers, then decide on a split of bandwidth for
each, but in practice most home ADSL users want more bandwidth than is
available, so you either end up using home's bandwidht for work, or
having a separate line.

>  --  This would be called a Service Access Loop in ATM
> parlance.  --  Thus ATM based DSL /technically/ /supports/ concurrent
> connections to multiple ISPs through the use of different PVCs.

But do they *use* that where you are either?

> I have used ATM DSL modems that supported up to eight different PVCs. As
> in the modem itself established the PVC using the PVI and SVI provided
> by the router.
>
>> In this country, only BT doesn't require authentication, because they
>> know which phone line you're on and use that instead
>
> That's because there is association with the physical port on the DSLAM
> with the phone line that is connected.  This pre-defined circuit makes
> it from the DSLAM through the provider's telco network to the router on
> the far side.  The router has different logical interfaces that
> represent the physical DSLAM port.  So there is a one-for-one mapping.
> As long as the association / mapping is maintained properly, you can
> easily know that logical port XYZ123 is phone number ABC-9876.
>
>> all other ISPs either require you to put a username and password in
>> the router, or they pre-configure it before they send the router out
>> to you,
>
> That may be the case where you are.  But where I'm from, all three of
> the ADSL ISPs (1 x ILEC and 2 x independent) used the one-for-one
> mapping described above.

Yep, but the only ISP that uses that here is the one who is BT, the
owner of the kit in the exchanges (ok there's an arm's length separation
between BT Openreach who own the kit and the wires, and BT Internet who
are the ISP)

> The PPPoE / DHCP / static configuration is
> actually (bridged / encapsulated) Ethernet frame riding across the DSL
> network -- which is more akin to point-to-point logical Ethernet links
> in this regard -- to the ISP who provides the counterpart for PPPoE /
> DHCP / static configuration.

I'm sure it varies around the planet, here ADSL uses ATM and PPPoE, VDSL
uses PPPoE

>> or use an automatic configuration system TR-069 which uses an
>> identifier (e.g. serial number) of the router to setup the parameters
>> for you.
>
> Things started with DHCP & static configuration and then progressed to
> PPPoE where I'm from.

PPoE still uses authentication here.

> The PPPoE enabled providers to care less (or not
> at all) about the one-for-one mapping described above and instead rely
> on PPPoE's authentication capabilities.  Thus the DSL became even more
> of a point-to-point Ethernet LAN.  Or, more accurately point (ISP) to
> multi-point (DSL subscribers) as subscriber to subscriber still needed
> to pass through the ISP's head end, for both layer 2 and layer 3.

On 7/25/21 1:03 PM, Andy Burns wrote:
> For ADSL smaller ISPs here likely use BT's DSLAMs, larger ISPs have
> provided their own, that's changing as more move to VDSL and use common
> MSANs where the fibre backhaul reaches the street cabinet.

I suspect the elephant in the room is the difference in population
density where you are vs where I am (from).

Where I'm from there is a lot of rural area where a single DSLAM may
have trouble covering line length to connect to 32 houses. So 8 and 16
port DSLAMs were common. In such sparse areas, each ISP deploying their
own DSLAM would be *EXTREMELY* inefficient if not wasteful.

> But do any providers make use of that? Technically it's possible but
> here it's never used.

It depends how you look at things.

The ILEC in my home town was particularly obstinate, and well known in
the country for being such. My understanding, based on reading that
I've done, is that more cooperative ILECs / CLECs /would/ do multiple
PVCs on xDSL connections. These LECs were usually found on the east &
west costs. I was stuck in the middle of the U.S.A. where we seemed to
be a decade behind in technology deployments.

If you remove the xDSL aspect from the link and instead focus on ATM
SALs, yes, such was done in my home town. Particularly with companies
like ISPs connecting into the ATM network to receive PVCs from all of
their customers. I'm told that such was also done for corporate /
enterprise companies for PVCs out to branch offices. After all, there
is exceedingly little difference between an ISP's connections to
residential users and an Enterprise's connections to branch offices. At
least form an ATM network operator's point of view.

> It might have been nice to provision a home ISP and a work ISP on
> the same line using different VCI/VPI numbers,

I tilted at this windmill from the standpoint of my customers. I tried
to get the phone company to provision a PVC from each of my customers
locations to a common ISP and then between their locations. The idea
was to divide the traffic such that site-to-site traffic went over one
PVC and site-to-Internet traffic went over a different PVC.
Unfortunately / sadly, I never got the cooperation from the ILEC. So
instead, all site-to-site traffic went over the PVC to the ISP where it
tromboned to other sites.

> most providers used the same VCI/VPI nunbers,

VPI 8 and VCI 35 were quite common in the mid-west. I remember hearing
of other common pairs for different regions of the U.S.A.

The very nature of how ATM works means that all the customers could use
the same VPI / VCI pair without conflicting with each other. :-)

> I can only think of one that even used different numbers, then decide
> on a split of bandwidth for each, but in practice most home ADSL
> users want more bandwidth than is available, so you either end up
> using home's bandwidht for work, or having a separate line.

I had a number of customers that had an xDSL connection for the servers
(on the Internet with static IPs) and a DOCSIS connection for general
Internet surfing (access to the Internet via NAT). Then it simply
became a configuration of which default gateway does this device use;
..254 for DOCSIS / NAT or .253 for xDSL. (DHCP provided .254. Servers /
specific clients were configured with .253 for special use cases.)
There was usually some sort of fail over outgoing access to the Internet
on each router in case it's local / preferred connection was down.

> But do they *use* that where you are either?

I never heard about it being used on ADSL connections in my area. I did
hear about it being used on ADSL connections on the coasts.

Voice over DSL was an option on the coasts. My ILEC laughed at me when
I asked about VoDSL in my area.

> Yep, but the only ISP that uses that here is the one who is BT, the
> owner of the kit in the exchanges (ok there's an arm's length separation
> between BT Openreach who own the kit and the wires, and BT Internet who
> are the ISP)

We have a similar arms reach / legal business entities owned by the same
corporate overlord, between the ILEC who owned the cable plant and
DSLAMs and the and the ILEC with their ISP hat on.

I saw cases where the same ISP would use more than one different method
depending on the customer. Basic DHCP / static for some customers and
PPPoE for other customers. I don't recall what the differentiation was.
It may have been a multi-year migration. I did my best to avoid PPPoE
because of the complications related to MTU / MSS.

> I'm sure it varies around the planet, here ADSL uses ATM and PPPoE, VDSL
> uses PPPoE

ADSL started as Frame Relay, migrated to ATM, and then migrated to
something more IP native. (I don't know the particulars about the last
configuration as I changed job roles.)

> PPoE still uses authentication here.

I'm not aware of PPPoE, or it's underlying PPP protocol, /not/ using
/authentication/. Even if the credentials are null, they are still used
by the underlying PPP protocol.

Aside: Yes, "PPP protocol" is accurate because "PPP" is a proper name
identifying specific technology. I could have said "underlying Point
to Point Protocol" if I wanted to expand it.

--
Grant. . . .
unix || die

Grant Taylor wrote:

> I did my best to avoid PPPoE because of the complications related to MTU
> / MSS.

I run openWRT on a VDSL capable router, specifically so I can force
baby-jumbo on the VLAN of the WAN interface, to keep up at 1500 bytes ...

Spiros Bousbouras <spibou@gmail.com> wrote:
>Where "this country" means the U.K. So if it's an xDSL network then it is
>physically possible for the packets to travel from any home router to several
>ISPs. Who owns the routers which decide which ISP the packets go to ? Is
>it BT ?

BT determines where the cables are connected up. In the case of DSL,
the DSLAM can be connected to any one of a number of outgoing networks.
In the case of other kinds of telco service, likely someone has to go
out and punch down cross-connect wires from one place to another.

But either it is a virtual or a physical wire from one point to another.
It's not a cloud, it's a single line.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Grant Taylor <gtaylor@tnetconsulting.net> wrote:
>Where I'm from there is a lot of rural area where a single DSLAM may
>have trouble covering line length to connect to 32 houses. So 8 and 16
>port DSLAMs were common. In such sparse areas, each ISP deploying their
>own DSLAM would be *EXTREMELY* inefficient if not wasteful.

Where I am, we have low population density, but only one DSL provider,
namely the telco that owns the local loops. So that's who owns the
DSLAM and when you get out onto the vast and dizzying internet, you are
doing so from an IP address owned by them. This is typical of much of
rural America.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Scott Dorsey <kludge@panix.com> wrote:
> Grant Taylor <gtaylor@tnetconsulting.net> wrote:
> >Where I'm from there is a lot of rural area where a single DSLAM may
> >have trouble covering line length to connect to 32 houses. So 8 and 16
> >port DSLAMs were common. In such sparse areas, each ISP deploying their
> >own DSLAM would be *EXTREMELY* inefficient if not wasteful.
>
> Where I am, we have low population density, but only one DSL provider,
> namely the telco that owns the local loops. So that's who owns the
> DSLAM and when you get out onto the vast and dizzying internet, you are
> doing so from an IP address owned by them. This is typical of much of
> rural America.

In the UK, in more rural areas it's less common for non-BT ISPs to have
DSLAMs at the exchange (central office). Exchanges are typically every few
miles, and in particularly rural areas may serve few customers (probably >32
though, with a line length of a few km). So your line terminates in a BT
Openreach-owned DSLAM, but then runs over a virtual tunnel to your ISP (I'm
not sure if it's an ethernet VLAN or something else). Exchanges were
typically sizeable windowless buildings with Strowger switches, nowadays
they can be simple equipment cabinets by the roadside (particularly with
VDSL where each cabinet becomes a mini exchange).

You contract service from your ISP, who routes your packets onto the
internet. Your ISP subcontracts your DSL local loop from BT Openreach. If
you have a fault on your local loop you have to contact your ISP who raises
a ticket with Openreach.

Before VDSL, if your exchange became populated enough, your ISP may decide
to install their own DSLAM, and so your loop is physically jumpered onto
their rack rather than the Openreach one. That saves them some money as
they don't have to rent Openreach's DSLAM (just their power and rack space)
and they aren't running a million tunnels back to their datacentre as they
can terminate directly at their equipment in the exchange. They then just
have to rent fibre backhaul from your exchange to their datacentre.

All of this is transparent to the customer - for anyone with an Openreach
connection (almost everyone, since BT were the nationalised telco) they have
a choice of ISPs. The details only matter to the speed you get, the price
you pay, and some edge cases when switching from one ISP to another.

Theo

Spiros Bousbouras <spibou@gmail.com> writes:

>> You tell it via the "default route" you setup when you configure it.
>
> I never did any such configuring on my current router. But , since it was
> provided by my ISP , it probably came preconfigured.

There is a protocol commonly used for this sort of thing, it's called
DHCP. Basically your router sends and receives broadcast packets and
accepts any responses which contain an IP address and default
route.

DHCP's not the only option, PPP is also used apparently since others
mentioned it. My country implemented ADSL usually with RFC1483 where
ethernet packets are stuffed into ATM cells. Awful for efficiency, about
15% wasted on framing total (TCP+IP+Ethernet+ATM headers). Although I
assume PPP doesn't help with that much.

> But this leads to another question : what if someone enters a route
> not for an ISP they are subscribing to ?

Your router only talks to the ISP's router and the ISP's router will
likely drop such packets on the floor. Routers route what they're
configured to route where they are configured to route it. And if no
route exist, well, your bits aren't going to go anywhere.

On 7/25/21 11:42 AM, Spiros Bousbouras wrote:
> I never did any such configuring on my current router. But , since
> it was provided by my ISP , it probably came preconfigured.

Yes, many ISPs that provide equipment tend to pre-configure as much of
it as they can with reasonable effort.

> But this leads to another question : what if someone enters
> a route not for an ISP they are subscribing to ?

I suspect that the worst that will happen is that things simply won't work.

> I'm guessing that some authentication will fail but if they somehow
> manage to crack the authentication process then they can get internet
> access without paying an ISP , right ?

The nature of how ISP networks work tends to be myopic, despite
technical capability for sharing.

Chances are extremely good that, without someone at the ISP or telco
reconfiguring something, there is nothing that an ISP subscriber can do
to access another ISP's network. As in traffic will never make it from
the circuits associated with ISP A over to ISP B.

> I was reading earlier en.wikipedia.org/wiki/TR-069

I don't think that TR-069 will be of any use if there is not a
functional communications path.

> and they say that routers are crackable.

Almost always.

> The setting is different but if an outsider can crack a router then
> I'm guessing that the owner can too.

Usually. Though I've found that often, external actors are more
motivated than equipment owners.

--
Grant. . . .
unix || die

On 7/26/21 10:04 AM, Anssi Saari wrote:
> DHCP's not the only option, PPP is also used apparently since others
> mentioned it.

I think you mean PPP-over-Ethernet, or PPPoE.

Yes, PPPoE uses PPP as the base protocol, but there is more to PPPoE
that means that it can't be used interchangeable with (just) PPP.

> My country implemented ADSL usually with RFC1483 where ethernet
> packets are stuffed into ATM cells. Awful for efficiency, about 15%
> wasted on framing total (TCP+IP+Ethernet+ATM headers). Although I
> assume PPP doesn't help with that much.

My understanding is that PPPoE also uses RFC 1483 Ethernet Bridging.
It's TCP+IP+PPPoE+Ethernet+ATM in that case.

There are other was to put IP, and likely PPP(oE) on ATM, but they are
seldom done as (over) Ethernet has become the defacto standard.

> Your router only talks to the ISP's router ....

Likely not even that.

The OPs router will send frames into the ether looking for the router
it's configured to talk to. It will extremely likely be unable to find
said router, thus won't talk to any router.

> Routers route what they're configured to route where they are
> configured to route it. And if no route exist, well, your bits aren't
> going to go anywhere.

Agreed. However, "default gateways" on the ISP's router tend to mean
that they will route just about everything (unless they've been
configured to reject something).

Aside: "gateway" and "router" are the same thing in this context.
Different terms that imply when the different terms for the same thing
was used.

--
Grant. . . .
unix || die

Grant Taylor <gtaylor@tnetconsulting.net> writes:

> There are other was to put IP, and likely PPP(oE) on ATM, but they are
> seldom done as (over) Ethernet has become the defacto standard.
>
>> Your router only talks to the ISP's router ....
>
> Likely not even that.

I was really trying to keep this mostly on the IP level since that's
what the OP asked about. The physical level isn't really relevant to
him. I guess I should've made that clear. And left out all the stuff
about the low level stuff.

> The OPs router will send frames into the ether looking for the router
> it's configured to talk to. It will extremely likely be unable to
> find said router, thus won't talk to any router.

I have no idea what you mean here. How does he get online then? And what
does his router actually connect to then? On the IP level? In my
understanding communication on IP level is computer to router to router
to router to eventual server.

On 25/07/2021 19:30, Spiros Bousbouras wrote:
> I'm asking for my general education so any reply for any location and any
> set up would be interesting to me.

There's a good explanation of how BT implemented ADSL in the UK here.
<https://kitz.co.uk/adsl/equip.htm>

It's a bit dated in that it only covers up to ADSL but it's not wrong.

The only area where it falls down a bit is that when it refers to ISPs
it does so in terms of larger ISPs that provide their own kit. It's
perfectly possible for a small ISP to buy in everything from BT or one
of the larger ISPs (or both at the same time for different exchanges)
and merely handle the billing relationship with the householder.

Typically these are ones that want to concentrate on, for example,
providing web hosting and business web services rather than being a
'hardcore' ISP.

Finally there is a last type of ISP, less common now, which is a purely
virtual ISP run on behalf of a large supermarket chain or energy
supplier / utility company.

--
Bruce Horrocks
Surrey, England