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Router sequence of operations



 
 
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  #1  
Old November 22nd 14, 09:44 AM posted to uk.telecom.broadband
Graham J[_2_]
external usenet poster
 
Posts: 723
Default Router sequence of operations

Can anybody help me with an authoritative reference explaining exactly
what happens as a router makes or loses an internet connection, please?

Modem component sees the ADLS or VDSL signal, trains, and after about a
minute achieves sync.

Router component sees this, sends the PPP authentication, and in due
course receives an IP address, DNS, and routing information. We know
this sometimes takes several tries - so it could be a minute or two.

This sequence is much the same whether the modem and router are separate
components, or integrated into a single box. It's also similar for ADSL
and FTTC using VDSL.

If the modem loses sync, then the connection fails, and the process
repeats - the modem re-acquires sync, then the router re-authenticates.

So:

While the connection is up, does the router ever repeat the
authentication process?

Does it ever happen that sync is maintained - but the PPP session is lost?

If so, what prompts the router to restart the authentication process?

TIA

--
Graham J


  #2  
Old November 22nd 14, 12:41 PM posted to uk.telecom.broadband
The Natural Philosopher
external usenet poster
 
Posts: 2,728
Default Router sequence of operations

On 22/11/14 09:44, Graham J wrote:
Can anybody help me with an authoritative reference explaining exactly
what happens as a router makes or loses an internet connection, please?

Modem component sees the ADLS or VDSL signal, trains, and after about a
minute achieves sync.

Router component sees this, sends the PPP authentication, and in due
course receives an IP address, DNS, and routing information. We know
this sometimes takes several tries - so it could be a minute or two.

This sequence is much the same whether the modem and router are separate
components, or integrated into a single box. It's also similar for ADSL
and FTTC using VDSL.

If the modem loses sync, then the connection fails, and the process
repeats - the modem re-acquires sync, then the router re-authenticates.

So:

While the connection is up, does the router ever repeat the
authentication process?

yes.

Does it ever happen that sync is maintained - but the PPP session is lost?


yes

If so, what prompts the router to restart the authentication process?


it gets a bad response or no resposnse at the PPP level


Some detail:

The training process is one of selecting narrow bands of frequencies
that work, or don't work. These frequencies are in the LW/MW/SW radio
band are all are subject to interference from a variety of sources, ADSL
on adjacent lines being one, and MW transmitters another.

Once the basic ADSL link is UP, you are connected to the DSLAM at the
exchange.

The next step is to send PPP over ATM frames to the ISP of choice. You
do this by FIRST sending your name/password to BTs own Radius servers
which proxy for your ISP, and accept your connection, and then BT sets
up an ATM virtual circuit over its backhaul to the ISP itself where you
log in again, and get a basic IP link set up and get given your DHCP
info - what IP addrress to use and if you use it, what DNS servers to use.

That's why there is a bit of ATM configuration in your router - VCI etc etc.

NOW: its possible for sync to the DSLAM to fail, if noise on the line
happens, and you will then re-sync to the exchange without upsetting tor
VPC back to the ISP. So you can get retrains occasionally.

It is also possible for the ISP to disconnect and require
re-authentication (actually with CHAP you are constantly
re-authenticating anyway) and the ISP may issue you with a new IP
address and or DNS target as well.

Quality routers will have diagnostics and logs to show this process in
action and information about what frequencies are in use and whether or
not the ATM based backhaul is working OK.

HTH.


TIA



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. - Erwin Knoll
  #3  
Old November 22nd 14, 02:46 PM posted to uk.telecom.broadband
Graham J[_2_]
external usenet poster
 
Posts: 723
Default Router sequence of operations

The Natural Philosopher wrote:

[snip]

If the modem loses sync, then the connection fails, and the process
repeats - the modem re-acquires sync, then the router re-authenticates.

So:

While the connection is up, does the router ever repeat the
authentication process?

yes.


Is there a specification that routers should adhere to saying how
frequently the authentication process should be repeated?

Does it ever happen that sync is maintained - but the PPP session is
lost?


yes

If so, what prompts the router to restart the authentication process?


it gets a bad response or no response at the PPP level


What you write is tautological. If it doesn't restart the
authentication process then it will not send a PPP request.

So what causes the router to send a PPP request, it the PPP session is
already up?

Some detail:

The training process is one of selecting narrow bands of frequencies
that work, or don't work. These frequencies are in the LW/MW/SW radio
band are all are subject to interference from a variety of sources, ADSL
on adjacent lines being one, and MW transmitters another.

Once the basic ADSL link is UP, you are connected to the DSLAM at the
exchange.


Understood.

The next step is to send PPP over ATM frames to the ISP of choice. You
do this by FIRST sending your name/password to BTs own Radius servers
which proxy for your ISP, and accept your connection, and then BT sets
up an ATM virtual circuit over its backhaul to the ISP itself where you
log in again, and get a basic IP link set up and get given your DHCP
info - what IP addrress to use and if you use it, what DNS servers to use.

That's why there is a bit of ATM configuration in your router - VCI etc
etc.


Understood.

NOW: its possible for sync to the DSLAM to fail, if noise on the line
happens, and you will then re-sync to the exchange without upsetting the
VPC back to the ISP. So you can get retrains occasionally.


Yes, I've seen that happen

It is also possible for the ISP to disconnect and require
re-authentication (actually with CHAP you are constantly
re-authenticating anyway


How frequently?

) and the ISP may issue you with a new IP
address and or DNS target as well.


[snip]

The case in point is an Openreach-supplied VDSL modem connected to the
Ethernet port on a Vigor 2820 router; at a site which is unattended.

From time to time the connection fails. (Actually twice in the first
two weeks of service, both times mid-morning, first for about an hour,
the second time for about 15 minutes.) The router only shows how long
the WAN connection has been up, and the VDSL modem tells us nothing
useful, given that there is nobody on site to look at its green lights.
I have nothing at the site that will receive syslog output.

The ISP (Zen Internet) can only confirm that the service disconnected.
The information they get from Openreach tells them the number of
disconnections in the previous 24 hours, but nothing useful like exactly
when, or whether the cause was authentication failure, or sync failure.
Neither can Openreach tell them the error counts on the VDSL service,
or SNR margin and loop attenuation; and of course I can't find that out
from the VDSL modem; so I can't tell whether the connection is marginal.

I monitor using F8Lure so I see the exact disconnection and reconnection
times.

So I'm looking for information to understand all the possible failure
mechanisms.

--
Graham J


  #4  
Old November 22nd 14, 03:26 PM posted to uk.telecom.broadband
The Natural Philosopher
external usenet poster
 
Posts: 2,728
Default Router sequence of operations

On 22/11/14 14:46, Graham J wrote:
The Natural Philosopher wrote:

[snip]

If the modem loses sync, then the connection fails, and the process
repeats - the modem re-acquires sync, then the router re-authenticates.

So:

While the connection is up, does the router ever repeat the
authentication process?

yes.


Is there a specification that routers should adhere to saying how
frequently the authentication process should be repeated?

Does it ever happen that sync is maintained - but the PPP session is
lost?


yes

If so, what prompts the router to restart the authentication process?


it gets a bad response or no response at the PPP level


What you write is tautological. If it doesn't restart the
authentication process then it will not send a PPP request.

it is sending PPP packets all the time, some are keepalives and some
contain CHAP authentication packets. And some contain user data.

http://en.wikipedia.org/wiki/Point-t...tocol_over_ATM
http://en.wikipedia.org/wiki/Challen...ation_Protocol


So what causes the router to send a PPP request, it the PPP session is
already up?

timers...? at either end.

Some detail:

The training process is one of selecting narrow bands of frequencies
that work, or don't work. These frequencies are in the LW/MW/SW radio
band are all are subject to interference from a variety of sources, ADSL
on adjacent lines being one, and MW transmitters another.

Once the basic ADSL link is UP, you are connected to the DSLAM at the
exchange.


Understood.

The next step is to send PPP over ATM frames to the ISP of choice. You
do this by FIRST sending your name/password to BTs own Radius servers
which proxy for your ISP, and accept your connection, and then BT sets
up an ATM virtual circuit over its backhaul to the ISP itself where you
log in again, and get a basic IP link set up and get given your DHCP
info - what IP addrress to use and if you use it, what DNS servers to
use.

That's why there is a bit of ATM configuration in your router - VCI etc
etc.


Understood.

NOW: its possible for sync to the DSLAM to fail, if noise on the line
happens, and you will then re-sync to the exchange without upsetting the
VPC back to the ISP. So you can get retrains occasionally.


Yes, I've seen that happen

It is also possible for the ISP to disconnect and require
re-authentication (actually with CHAP you are constantly
re-authenticating anyway


How frequently?


I would say minutes not hours. It all depends on how the gear is set up.


) and the ISP may issue you with a new IP
address and or DNS target as well.


[snip]

The case in point is an Openreach-supplied VDSL modem connected to the
Ethernet port on a Vigor 2820 router; at a site which is unattended.

From time to time the connection fails. (Actually twice in the first
two weeks of service, both times mid-morning, first for about an hour,
the second time for about 15 minutes.) The router only shows how long
the WAN connection has been up, and the VDSL modem tells us nothing
useful, given that there is nobody on site to look at its green lights.
I have nothing at the site that will receive syslog output.

The ISP (Zen Internet) can only confirm that the service disconnected.
The information they get from Openreach tells them the number of
disconnections in the previous 24 hours, but nothing useful like exactly
when, or whether the cause was authentication failure, or sync failure.


Zen should be able top see that and also tthe router may log what
happened in its own logs.

Neither can Openreach tell them the error counts on the VDSL service,
or SNR margin and loop attenuation; and of course I can't find that out
from the VDSL modem; so I can't tell whether the connection is marginal.

I monitor using F8Lure so I see the exact disconnection and reconnection
times.

So I'm looking for information to understand all the possible failure
mechanisms.

get a VDSL router that can do some logging.



--
Everything you read in newspapers is absolutely true, except for the
rare story of which you happen to have first-hand knowledge. - Erwin Knoll
  #5  
Old November 22nd 14, 03:47 PM posted to uk.telecom.broadband
grinch
external usenet poster
 
Posts: 68
Default Router sequence of operations

On 22/11/14 14:46, Graham J wrote:
The Natural Philosopher wrote:

[snip]


The case in point is an Openreach-supplied VDSL modem connected to the
Ethernet port on a Vigor 2820 router; at a site which is unattended.



From time to time the connection fails. (Actually twice in the first
two weeks of service, both times mid-morning, first for about an hour,
the second time for about 15 minutes.) The router only shows how long
the WAN connection has been up, and the VDSL modem tells us nothing
useful, given that there is nobody on site to look at its green lights.



I have nothing at the site that will receive syslog output.


The 2820 can syslog to a usb stick in its usb port and gives good
info to the state of the PPP session. As it is not directly connected to
the actual VDSL I don't think you will get any line stats from it.

Set the time up using an NTP server then you know the time is correct

It has the ability to send keepalives and also to ping a given IP
address, if it cant ping said address I am not sure if it will try to
re-authenticate again, try google for their website, but I think it is
www.draytek.co.uk.

The ISP (Zen Internet) can only confirm that the service disconnected.
The information they get from Openreach tells them the number of
disconnections in the previous 24 hours, but nothing useful like exactly
when, or whether the cause was authentication failure, or sync failure.
Neither can Openreach tell them the error counts on the VDSL service,
or SNR margin and loop attenuation; and of course I can't find that out
from the VDSL modem; so I can't tell whether the connection is marginal.

I monitor using F8Lure so I see the exact disconnection and reconnection
times.

So I'm looking for information to understand all the possible failure
mechanisms.



try google for PPP CHAP VDSL IP PPPoE XTALK REIN

Have a rummage round in wikipedia you should find an explanation of how
dsl works just ignore what connectivity method it uses adsl/vdsl

There are routers which directly use the vdsl so you don't need the BT
modem such as a Cisco 867 but that is against the BT t&Cs.
  #6  
Old November 22nd 14, 04:16 PM posted to uk.telecom.broadband
Graham J[_2_]
external usenet poster
 
Posts: 723
Default Router sequence of operations

The Natural Philosopher wrote:

[snip]


http://en.wikipedia.org/wiki/Point-t...tocol_over_ATM
http://en.wikipedia.org/wiki/Challen...ation_Protocol


Thanks - and to quote:

"At random intervals the authenticator sends a new challenge to the peer"


The ISP (Zen Internet) can only confirm that the service disconnected.
The information they get from Openreach tells them the number of
disconnections in the previous 24 hours, but nothing useful like exactly
when, or whether the cause was authentication failure, or sync failure.


Zen should be able top see that


I asked them, and specifically - no - they can't see the cause of the
failure. They might be able to determine if the line is in sync when
the connection has failed, but that relies on me seeing the fault and
ringing them to ask.

get a VDSL router that can do some logging.


I have a Vigor 2860 ready to take to the site for just that purpose.


--
Graham J


  #7  
Old November 22nd 14, 04:31 PM posted to uk.telecom.broadband
Graham J[_2_]
external usenet poster
 
Posts: 723
Default Router sequence of operations

grinch wrote:
[snip]


I have nothing at the site that will receive syslog output.


The 2820 can syslog to a usb stick in its usb port and gives good
info to the state of the PPP session. As it is not directly connected to
the actual VDSL I don't think you will get any line stats from it.

Set the time up using an NTP server then you know the time is correct


Might be useful - but necessitates a trip to the site to plug in the USP
stick, and a second trip to collect it.

When the connection is up I have remote management of the router. Can I
then use the router to interrogate the contents of the USB stick? OK I
will have to read the manual and try it on a test router.


It has the ability to send keepalives and also to ping a given IP
address, if it cant ping said address I am not sure if it will try to
re-authenticate again, try google for their website, but I think it is
www.draytek.co.uk.


It uses this mechanism to decide whether to bring up a backup WAN
connection using 3G. Also it maintains a VPN. Not clear that it
invokes a re-authentication cycle.

--
Graham J

  #8  
Old November 22nd 14, 05:43 PM posted to uk.telecom.broadband
grinch
external usenet poster
 
Posts: 68
Default Router sequence of operations

On 22/11/14 16:31, Graham J wrote:
grinch wrote:
[snip]


I have nothing at the site that will receive syslog output.


The 2820 can syslog to a usb stick in its usb port and gives good
info to the state of the PPP session. As it is not directly connected to
the actual VDSL I don't think you will get any line stats from it.

Set the time up using an NTP server then you know the time is correct


Might be useful - but necessitates a trip to the site to plug in the USP
stick, and a second trip to collect it.





When the connection is up I have remote management of the router. Can I
then use the router to interrogate the contents of the USB stick? OK I
will have to read the manual and try it on a test router.


No you can read it remotely once installed but put a reasonable sized
USB stick as if memory serves it's about 10MB per day .

Please don't take that as fact I have not used my 2820 since I got vdsl
installed 2 years ago.You can of course delete days when nothing happens






It has the ability to send keepalives and also to ping a given IP
address, if it cant ping said address I am not sure if it will try to
re-authenticate again, try google for their website, but I think it is
www.draytek.co.uk.


It uses this mechanism to decide whether to bring up a backup WAN
connection using 3G. Also it maintains a VPN. Not clear that it
invokes a re-authentication cycle.


Why not suck it and see I don't think it will break anything

  #9  
Old November 26th 14, 12:47 PM posted to uk.telecom.broadband
Martin Brown
external usenet poster
 
Posts: 343
Default Router sequence of operations

On 22/11/2014 16:16, Graham J wrote:
The Natural Philosopher wrote:

[snip]


http://en.wikipedia.org/wiki/Point-t...tocol_over_ATM
http://en.wikipedia.org/wiki/Challen...ation_Protocol


Thanks - and to quote:

"At random intervals the authenticator sends a new challenge to the peer"


The ISP (Zen Internet) can only confirm that the service disconnected.
The information they get from Openreach tells them the number of
disconnections in the previous 24 hours, but nothing useful like exactly
when, or whether the cause was authentication failure, or sync failure.


Zen should be able top see that


I asked them, and specifically - no - they can't see the cause of the
failure. They might be able to determine if the line is in sync when
the connection has failed, but that relies on me seeing the fault and
ringing them to ask.


Most of the failures I encounter on my rural line are where the sync is
nominally fine but the transport mechanism and SNR margin has failed.
Analysis of the SNR margins shows completely insane values but the modem
fails to do anything useful about it and presses on regardless. In this
state all packets get dropped on the floor by timeout/retries.

User disconnect and reconnect notably fail to do anything useful at all!

The modem can be roused from this state only by cycling the power or a
full hardware reset from its hidden "advanced" menu. If you could detect
this bad state at the far end and force a reboot that might help.

My previous routers had similar behaviour but slightly worse SNR so I
use the present one despite its rare but annoying need for hard reset. I
don't know what it is about rural lines but they have interesting
faults. I have had two days without dialtone where only one phone would
ring and although CLID was displayed answering the phone didn't work!

Another peculiarity I have seen with some routers is that to make them
be stable for streaming video or audio you have to disable plug & play.
I have no idea why this works but it does!

get a VDSL router that can do some logging.


I have a Vigor 2860 ready to take to the site for just that purpose.


You might want to consider putting the errant router on a clock to cycle
the power once a day. I am just celebrating being back online after two
days with no dialtone or ADSL due to OpenReach handiwork.

I am hoping for no further disruption for a while.

--
Regards,
Martin Brown
  #10  
Old November 26th 14, 03:46 PM posted to uk.telecom.broadband
Graham J[_2_]
external usenet poster
 
Posts: 723
Default Router sequence of operations

Martin Brown wrote:
[snip]


I
don't know what it is about rural lines but they have interesting
faults. I have had two days without dialtone where only one phone would
ring and although CLID was displayed answering the phone didn't work!


Have exactly this fault in North Lopham (Norfolk) since yesterday. No
dial tone, just a faint clicking sound. Incoming calls ring the phone,
but can't be answered - the caller continues to hear ring tone.

ADSL is just about connecting at dial-up speeds.

ISP tells me that it is a widespread fault which will require "traffic
management" to cure - not expected to be fixed until Friday.

I suspect exchange equipment failure ...

--
Graham J


 




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