[HLUG] Limit to number of computers connected to BT broadband?

Sat Jul 22 11:27:25 UTC 2017

Julian,

Assuming that fibre is similar to ADSL in that your ISP assigns a
single public IP address to your modem/router and that every PC on
your LAN only has a private IP address in the 192.168.1.0/24 range and
has to rely on NAT being performed at the router in order to access
the internet... how does BT even know how many different PCs on your
LAN are making DNS requests? (Assuming that each PC on the LAN has the
modem/router's private IP address set as their DNS server and it's
only the modem/router itself making DNS requests to BT's DNS server?)

George,

As Steve said, it may be worth working methodically down the chain of
series connected routers to see if you can pinpoint a particular node
at which the problems occur.

Physically connect a computer (no wireless!) to the first router in
your chain of routers - the one that connects directly to your
broadband or fibre.
- Ping the IP addresses of each router in your chain of routers. Note
any failures.
- Ping an external IP address. e.g. 216.58.206.46 (google.com)
- Ping an external hostname e.g. google.com
now move your computer and connect it directly to the second router in
your chain of routers and repeat the all tests. You may need to flush
your computer's DNS cache between tests but unfortunately the command
to do this depends on your distro. Google it, I'm afraid! (In Windows
it is ipconfig /flushdns from a command prompt run in administrator
mode.)

I presume that out of all the routers you have linked in series, only
the one that directly connected to your incoming fibre connection
(Master) is configured with
- PPPoE mode (or whatever BT requires for a fibre/ADSL connection)?
- A unique private IP address (e.g. 192.168.1.1)
- An appropriate subnet mask (e.g. 255.255.255.0)
- A public DNS server's IP address (likely BT's DNS server)
- DHCP server enabled (set address range as appropriate)

The other three routers (Slaves) in the series should *probably* each
be configured with
- unique static IP addresses (e.g. 192.168.1.2 , 192.168.1.3 , 192.168.1.4)
- The same subnet mask (e.g. 255.255.255.0)
- gateway IP address set to the private IP of your Master router (e.g.
192.168.1.1)
- DNS server's IP address set to the private IP of your Master router
(e.g. 192.168.1.1)
- DHCP server disabled

This setup should give ensure you have only one router handling DHCP
and DNS requests for your entire LAN

Client PCs on your LAN should usually get their private IP addresses
via DHCP. This should ensure propagation of correct, working
networking settings from the Master router that is also acting as a
DHCP server.
If you must set a client PC to have a static private IP address, it
should be unique, it should be on the same subnet as above (e.g.
192.168.1.?), should have the same subnet mask as above (e.g.
255.255.255.0), and its gateway and DNS server addresses should both
be that of your Master router (e.g. 192.168.1.1 in the example above)

Possible other problems could be:
1. Some or all PCs or routers on your LAN are already trying to use
DNS servers other than BT's own and you've got "BT Parental Controls"
or "BT Protect" enabled for your BT account. BT won't allow the use of
different DNS servers while those options are enabled on as all the
filtering and blocking that those services provide requires the use of
their own DNS servers. Log into your BT account to find out if you've
got those and if they're enabled.
2. BT's DNS servers could just be having a bad day. See Julian's point
about using Google or OpenDNS instead.
3. You've accidentally assigned the same static private IP address to
one or more devices (routers or PCs) on your LAN.
4. You've got more than one of your routers acting as DHCP servers on
your LAN. Turn DHCP server functionality off on all but one of your
routers.

Write down all your ISP's connection settings before you start, just
in case you have to reset your master router to its factory defaults!
Take detailed notes of what changes you make to which devices and what
effect they have.
Some devices may require network services be restarted before changes
take effect, or may even require a reboot.

hope this helps,
Richard

On 22 July 2017 at 10:18, Julian Robbins via Herefordshire
<herefordshire at mailman.lug.org.uk> wrote:
> Hi everyone
>
> It may be that your hitting a limit for the max number of devices connected
> to a single fibre line for your isp wrt to the the number of devices
> getting DNS.
>
> You probably use upstream DNS from your isp.
>
> If they are setting a limit of number of devices on your account you could
> set one or more routers to use a different DNS like Google DNS on 8.8.8.8
> or 8.8.4.4 or open DNS perhaps
>
> That should fix your problem
>
> Julian
>
>
>
> On 22 Jul 2017 8:07 am, "Steve Horsfield via Herefordshire" <
> herefordshire at mailman.lug.org.uk> wrote:
>
>> Can all the devices see each other i.e. have you got one complete network?
>> Where in the series are the non-connecting devices, near or far from the
>> gateway device?
>>
>> Steve Horsfield
>>
>> On 22 July 2017 at 00:19, George DiceGeorge via Herefordshire <
>> herefordshire at mailman.lug.org.uk> wrote:
>>
>> > Ive got BT broadband,
>> >
>> > I had 4 routers linked together in series
>> >
>> > and at the end we were getting 20 meg on one computer
>> > and quite a few other devices connected
>> >
>> > but other devices couldnt get connected
>> >
>> > reporting DNS errors
>> > "The DNS server isn’t responding "
>> >
>> > Is there a limit to the number of devices i should chain and connect?
>> >
>> > Ive got more guests coming tomorrow
>> > and we want to connect more
>> > and skype etc....
>> >
>> > 2 of the routers are old linksys WRT54G s
>> >
>> > advice please
>> >
>> >
>> > george
>> >
>> >
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