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uk.telecom.broadband (UK broadband) (uk.telecom.broadband) Discussion of broadband services, technology and equipment as provided in the UK. Discussions of specific services based on ADSL, cable modems or other broadband technology are also on-topic. Advertising is not allowed.

(BT Broadband) home NW newbie, wired ADSL router-modem and Linux



 
 
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  #1  
Old August 21st 04, 11:53 PM posted to uk.telecom.broadband
a.n.other
external usenet poster
 
Posts: 3
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux


I've been using BT Broadband (i.e. the BT retail product) on a single
(W98) PC via a BT Voyager USB ADSL modem happily for a good while now.

I'm thinking of setting up a modest home network for the first time. I
think going wireless is a step too far for me at the moment, and I can
live with cables, so am thinking in terms of e.g. a Netgear DG834 wired
router modem.

Initially, I'd be adding probably one other Windows PC, but before too
long hopefully, a Linux (probably Redhat 9 or maybe Fedora FC 2) box.

I've found several very helpful guides on the web to setting up this kind
of thing, and it seems fairly doable for the Windows PCs, but I have a
question regarding connecting the Linux box.

I've used UNIX machines on the LAN at work for years, and increasingly so
Linux boxes. However, they all have static IP addresses and well-defined
gateway addresses.

I'm not clear how that will work when connected to BT Broadband via my
proposed router. I've read on the web that you can theoretically use DHCP,
and that the router (if smart enough) will automatically get the required
gateway address from the ISP, but this seems to depend on the ISP. Is this
likely to work with BT Broadband and this router?

Or is the gateway address actually something I can, and need to configure
myself in the router? (or a default?). I'd think this is still somewhat
dependent on the ISP though. Perhaps I should just phone up BT Btoadband
and ask, but I'm wary of getting passed to some premium phone number which
I can't afford.

Thanks for any pointers.



--

  #2  
Old August 22nd 04, 03:17 AM posted to uk.telecom.broadband
Sunil Sood
external usenet poster
 
Posts: 1,590
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux


"a.n.other" wrote in message
news:[email protected]
I'm not clear how that will work when connected to BT Broadband via my
proposed router. I've read on the web that you can theoretically use DHCP,
and that the router (if smart enough) will automatically get the required
gateway address from the ISP, but this seems to depend on the ISP. Is this
likely to work with BT Broadband and this router?


Yes.

Or is the gateway address actually something I can, and need to configure
myself in the router? (or a default?). I'd think this is still somewhat
dependent on the ISP though. Perhaps I should just phone up BT Btoadband
and ask, but I'm wary of getting passed to some premium phone number which
I can't afford.


If you wanted to give your PC's static (internal) IP addresses instead you
could..

Which ISP you use doesn't matter.

Regards
Sunil


  #3  
Old August 22nd 04, 03:53 AM posted to uk.telecom.broadband
MM
external usenet poster
 
Posts: 9
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux


"a.n.other" wrote in message
news:[email protected]

I've been using BT Broadband (i.e. the BT retail product) on a single
(W98) PC via a BT Voyager USB ADSL modem happily for a good while now.

I'm thinking of setting up a modest home network for the first time. I
think going wireless is a step too far for me at the moment, and I can
live with cables, so am thinking in terms of e.g. a Netgear DG834 wired
router modem.

Initially, I'd be adding probably one other Windows PC, but before too
long hopefully, a Linux (probably Redhat 9 or maybe Fedora FC 2) box.

I've found several very helpful guides on the web to setting up this kind
of thing, and it seems fairly doable for the Windows PCs, but I have a
question regarding connecting the Linux box.

I've used UNIX machines on the LAN at work for years, and increasingly so
Linux boxes. However, they all have static IP addresses and well-defined
gateway addresses.

I'm not clear how that will work when connected to BT Broadband via my
proposed router. I've read on the web that you can theoretically use DHCP,
and that the router (if smart enough) will automatically get the required
gateway address from the ISP, but this seems to depend on the ISP. Is this
likely to work with BT Broadband and this router?

Or is the gateway address actually something I can, and need to configure
myself in the router? (or a default?). I'd think this is still somewhat
dependent on the ISP though. Perhaps I should just phone up BT Btoadband
and ask, but I'm wary of getting passed to some premium phone number which
I can't afford.

Thanks for any pointers.



--


Most consumer grade stuff is very easy to setup. The DG834 will detect the
connection type - all you have to do is give it your BT username and
password - thats it. By default its internal DHCP server is on, and any PC
you plug into it will get an address in the range. Im not familiar with
Linux, but I guess youd just set your TCP stack to get a DHCp assigned
address - thats it...no more to it than that.

cheers
Mark


  #4  
Old August 22nd 04, 02:28 PM posted to uk.telecom.broadband
poster
external usenet poster
 
Posts: 1,542
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux

On 21 Aug 2004 in uk.telecom.broadband, "a.n.other" wrote:

I've been using BT Broadband (i.e. the BT retail product) on a single
(W98) PC via a BT Voyager USB ADSL modem happily for a good while now.


I'm not clear how that will work when connected to BT Broadband via my
proposed router. I've read on the web that you can theoretically use DHCP,
and that the router (if smart enough) will automatically get the required
gateway address from the ISP, but this seems to depend on the ISP. Is this
likely to work with BT Broadband and this router?


Cannot answer for what info you can get from that router, but as far as DHCP
is concerned, pretty much all the routers support it (enabled by default).
Getting the details using DHCP should certainly be fine for Windows, no idea
about the Linux box(es) but if you are going to use them as servers then you
would most likely (!) want fixed IPs for each one to be able to let the ADSL
router send data to them depending on port number. For example, I run a web
server application on PC #3, and incoming mail can arrive on PC #4 while any
PC can connect to any other using VNC (but I have fixed IP addresses so know
which PC is which, and from the internet, can connect to specific PCs (with
firewall rules to restrict where access can be achieved!).

For peace of mind, I'd suggest using fixed IP addresses for every type of
O.S. you use, simply so you can 'ping' a machine and know which it is if
for no other reason - can help if you end up with a hub at one end of the
house and the ADSL router at the other - it is then very easy to track data
through your network, watching for flashing LEDs from system A to system B
to check the cables etc etc. Here's an extract from my router's system
log, showing the DNS entries it has picked up from the ISP.

8/21/2004 00:37:13 PPP CHAP Authentication success
8/21/2004 00:37:13 PPP1: PPP IP address is 80.41.2.186
8/21/2004 00:37:13 PPP1: PPP Gateway IP address is 212.74.111.188
8/21/2004 00:37:13 PPP1: DNS Primary IP address is 80.225.252.186
8/21/2004 00:37:13 PPP1: DNS Secondary IP address is 80.225.252.178
8/21/2004 00:37:13 NAT/NAPT Session Start: VC# 0, WAN IP is 80.41.2.186
8/21/2004 00:37:13 Initialized NAT Virtual Servers.
8/21/2004 00:37:13 NAPT: many-to-one default session is up.
8/21/2004 00:37:14 PPP1 Session is up.

Or is the gateway address actually something I can, and need to configure
myself in the router? (or a default?). I'd think this is still somewhat
dependent on the ISP though.


On my LAN, Ive set the gateway address to be the router (10.0.0.100) while
the gateway address shown in the log above is nothing I need know - it is
the ISP end of my connection (but I've never needed to know it or had to
find it out, in the past 30 months or so, using ADSL)

Perhaps I should just phone up BT Btoadband and ask, but I'm wary of
getting passed to some premium phone number which I can't afford.


They might support specific routers (eg ones they supply) but all you need
to know are the primary and secondary DNS entries if you set up your PCs
to use fixed IP addresses, a fixed gateway address (that used for the
Netgear or any other ADSL modem/router) and then your choice of IPs for
the PCs themselves. I use 10.0.0.xxx for simplicity and ease or memory!!
  #5  
Old August 22nd 04, 03:21 PM posted to uk.telecom.broadband
sarah
external usenet poster
 
Posts: 26
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux

MM wrote:

all you have to do is give it your BT username and
password - thats it


I don't think BT Broadband uses a username and password
  #6  
Old August 22nd 04, 07:41 PM posted to uk.telecom.broadband
David Bradley
external usenet poster
 
Posts: 329
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux

On Sun, 22 Aug 2004 13:28:31 +0100, poster
wrote:

On 21 Aug 2004 in uk.telecom.broadband, "a.n.other" wrote:

I've been using BT Broadband (i.e. the BT retail product) on a single
(W98) PC via a BT Voyager USB ADSL modem happily for a good while now.


I'm not clear how that will work when connected to BT Broadband via my
proposed router. I've read on the web that you can theoretically use DHCP,
and that the router (if smart enough) will automatically get the required
gateway address from the ISP, but this seems to depend on the ISP. Is this
likely to work with BT Broadband and this router?


Cannot answer for what info you can get from that router, but as far as DHCP
is concerned, pretty much all the routers support it (enabled by default).
Getting the details using DHCP should certainly be fine for Windows, no idea
about the Linux box(es) but if you are going to use them as servers then you
would most likely (!) want fixed IPs for each one to be able to let the ADSL
router send data to them depending on port number. For example, I run a web
server application on PC #3, and incoming mail can arrive on PC #4 while any
PC can connect to any other using VNC (but I have fixed IP addresses so know
which PC is which, and from the internet, can connect to specific PCs (with
firewall rules to restrict where access can be achieved!).

For peace of mind, I'd suggest using fixed IP addresses for every type of
O.S. you use, simply so you can 'ping' a machine and know which it is if
for no other reason - can help if you end up with a hub at one end of the
house and the ADSL router at the other - it is then very easy to track data
through your network, watching for flashing LEDs from system A to system B
to check the cables etc etc. Here's an extract from my router's system
log, showing the DNS entries it has picked up from the ISP.

8/21/2004 00:37:13 PPP CHAP Authentication success
8/21/2004 00:37:13 PPP1: PPP IP address is 80.41.2.186
8/21/2004 00:37:13 PPP1: PPP Gateway IP address is 212.74.111.188
8/21/2004 00:37:13 PPP1: DNS Primary IP address is 80.225.252.186
8/21/2004 00:37:13 PPP1: DNS Secondary IP address is 80.225.252.178
8/21/2004 00:37:13 NAT/NAPT Session Start: VC# 0, WAN IP is 80.41.2.186
8/21/2004 00:37:13 Initialized NAT Virtual Servers.
8/21/2004 00:37:13 NAPT: many-to-one default session is up.
8/21/2004 00:37:14 PPP1 Session is up.

Or is the gateway address actually something I can, and need to configure
myself in the router? (or a default?). I'd think this is still somewhat
dependent on the ISP though.


On my LAN, Ive set the gateway address to be the router (10.0.0.100) while
the gateway address shown in the log above is nothing I need know - it is
the ISP end of my connection (but I've never needed to know it or had to
find it out, in the past 30 months or so, using ADSL)

Perhaps I should just phone up BT Btoadband and ask, but I'm wary of
getting passed to some premium phone number which I can't afford.


They might support specific routers (eg ones they supply) but all you need
to know are the primary and secondary DNS entries if you set up your PCs
to use fixed IP addresses, a fixed gateway address (that used for the
Netgear or any other ADSL modem/router) and then your choice of IPs for
the PCs themselves. I use 10.0.0.xxx for simplicity and ease or memory!!


I am surprised by some of responses given to the OP. I would say that
for the Windows OS then DHCP is a sensible choice as you will never
have a conflict of IP addresses. Also you won't have to enter the DNS
server IPs into each PC. However, there could be a need for a few of
the connected devices requiring a fixed IP address, such as Linux or
Unix boxes, or maybe printers. A mixed enviroment of both DHCP and
fixed IP numbers is permissable and quite easy to set up in the
router.

The router diagnostics will tell you where the DHCP IPs have been
issued and if everything is left powered up, the allocated numbers
will not change.

Your internal network should desirably have IP numbers in a "private
range" and these a
10.0.0.0 --- 10.255.255.255
172.16.0.0 --- 172.31.255.255
192.168.0.0 --- 192.168.255.255
There is a strong merit for simple networks to be in the 192.168.y.x
range where 'y' is best chosen between 10 and 253 and 'x' between 2
and 49 for use as fixed IPs and and above 50 for DHCP use. This
range of IP numbers is known as a Class 'C' address and therefore the
Netmask would be usually 255.255.255.0 It seems to be standard
practice for the router to be either 192.168.x.0 or 192.168.x.1 and I
see no reason to depart from this convention.

If you ever get into the realms of VPN you will find that making the
right choices now will save a lot of unpicking of IP numbers at a
later date.

Your router will contain your login details and, if this information
is correct, will make a successfull connection to your ISP which will
populated your router with a public IP address and DNS numbers plus a
few other bits of information. [If you have a fixed IP address this
is entered into the router].

Those 'boxes' that you have given fixed IP numbers to, may also
require you to add a gateway IP address; this being the IP number of
the router.

I have connected a router to BT Broadband and used only the login id,
no passwortd was required. It was, however, noted in the instructions
that if the choice of router "demanded" a password, then BT could be
used. When typing in the login id it is surprisingly easy to make a
mistake - I had to have six goes before I got it right!

I assume you know all about LPR printing so that you can have a common
printer for both your Windows and Linus/Unix boxes. However it is
interesting to note that some routers now come with a built in USB
port for printers.

All the above may help the OP in setting up his equipment; no doubt
there will be others who will have a pop at me for what is said here
but that's life on a newsgroup. You can't please everyone all of the
time!

David Bradley

  #7  
Old August 22nd 04, 11:39 PM posted to uk.telecom.broadband
a.n.other
external usenet poster
 
Posts: 3
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux

On Sun, 22 Aug 2004, David Bradley wrote:

I am surprised by some of responses given to the OP. I would say that
for the Windows OS then DHCP is a sensible choice as you will never
have a conflict of IP addresses. Also you won't have to enter the DNS
server IPs into each PC. However, there could be a need for a few of
the connected devices requiring a fixed IP address, such as Linux or
Unix boxes, or maybe printers. A mixed enviroment of both DHCP and
fixed IP numbers is permissable and quite easy to set up in the
router.

The router diagnostics will tell you where the DHCP IPs have been
issued and if everything is left powered up, the allocated numbers
will not change.

Your internal network should desirably have IP numbers in a "private
range" and these a
10.0.0.0 --- 10.255.255.255
172.16.0.0 --- 172.31.255.255
192.168.0.0 --- 192.168.255.255
There is a strong merit for simple networks to be in the 192.168.y.x
range where 'y' is best chosen between 10 and 253 and 'x' between 2
and 49 for use as fixed IPs and and above 50 for DHCP use. This
range of IP numbers is known as a Class 'C' address and therefore the
Netmask would be usually 255.255.255.0 It seems to be standard
practice for the router to be either 192.168.x.0 or 192.168.x.1 and I
see no reason to depart from this convention.

If you ever get into the realms of VPN you will find that making the
right choices now will save a lot of unpicking of IP numbers at a
later date.

Your router will contain your login details and, if this information
is correct, will make a successfull connection to your ISP which will
populated your router with a public IP address and DNS numbers plus a
few other bits of information. [If you have a fixed IP address this
is entered into the router].

Those 'boxes' that you have given fixed IP numbers to, may also
require you to add a gateway IP address; this being the IP number of
the router.



Many thanks for the comprehensive advice!
I haven't fully understood it all yet, but I now feel a lot more confident
about moving forward on this.


I have connected a router to BT Broadband and used only the login id,
no passwortd was required. It was, however, noted in the instructions
that if the choice of router "demanded" a password, then BT could be
used. When typing in the login id it is surprisingly easy to make a
mistake - I had to have six goes before I got it right!


Thanks for that. I was a bit worried about the router demanding a
password, since I don't currently use one, and was not even sure how to
set it up.


I assume you know all about LPR printing so that you can have a common
printer for both your Windows and Linus/Unix boxes. However it is
interesting to note that some routers now come with a built in USB
port for printers.


At work, I'm used to network-connected printers (usually accessible from
Microsoft and Linux print-servers), so the idea of a networked printer
definitely appeals. My present one is not USB, but the one I plan to buy
is; neither has an ethernet card possibility though.

All the above may help the OP in setting up his equipment; no doubt
there will be others who will have a pop at me for what is said here
but that's life on a newsgroup. You can't please everyone all of the
time!


You have certainly given me the confidence that what I want to do should
be not too difficult, given a bit more study and a bit of patience, so
many thanks.

Thanks too for all other contributions. Even if I haven't understood them
all fully yet, be sure that I will study them carefully and I'm sure will
learn from all of them.

Regards,

NWM
--

  #8  
Old August 23rd 04, 12:13 AM posted to uk.telecom.broadband
David Bradley
external usenet poster
 
Posts: 329
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux

On Sun, 22 Aug 2004 22:28:56 GMT, will kemp
wrote:

On Sat, 21 Aug 2004 22:53:47 +0100, a.n.other wrote:

I'm not clear how that will work when connected to BT Broadband via my
proposed router. I've read on the web that you can theoretically use DHCP,
and that the router (if smart enough) will automatically get the required
gateway address from the ISP, but this seems to depend on the ISP. Is this
likely to work with BT Broadband and this router?

Or is the gateway address actually something I can, and need to configure
myself in the router? (or a default?). I'd think this is still somewhat
dependent on the ISP though.


there are a few different ways such a network connection could be
configured. one possibility that has been suggested is to give all
computers their own internet-routable ip addresses. this isn't really all
that practical in these days of ip address shortage - and it's not
necessary either, except in certain circumstances (which probably don't
apply to what you're doing).

to understand how this stuff works, you have to first understand the
difference between ip addresses that are routable via the internet and ip
addresses which are only routable locally.

in general, any computer connected to the internet can connect to any
other ip address - the information on how to get from one to the other is
kept by routers along the way. however, there are 3 (if i remember
correctly) blocks of ip addresses which are reserved for local network
use. packets addressed to ip addresses in these blocks should (a) never be
sent out of the local network to the internet and (b) if they do get out
to the internet, should be dropped by the first router they come to and
not passed on.

10.0.0.0/8 and 192.168.0.0/16 are two of these blocks. i' m pretty sure
there's a third one, but can't for the life of me remember what it is.
anyway, 10.0.0.0/8 is generally used as a single subnet (used to be called
a "class 'A'" subnet), with 4,294,967,296 addresses in it. the
192.168.0.0/16 ("class 'B'") block is normally used as 256 "/24" ("class
'C'") subnets (with 256 addresses in each one). the most commonly used
ones would be 192.168.0.0/24 and 192.168.1.0/24 - one or the other of
these is almost always used for local networks like the one you want to
set up.

i realise the above numbers probably look like gobbledygook! in
particular, what on earth are all those "/24" etc bits all about??? well,
to fully understand ip addressing, you need to have a reasonable grasp of
binary - and i'll leave you to find out about that yourself! (if you don't
already know it.)

basically, each of the numbers separated by dots in an ip address (e.g.
192.168.0.27) are 8-bit binary numbers (usually known in this context as
"octets"). an 8-bit binary number can have a (decimal) value from 0 to 255
- in other words, 256 different values.

the part of the network address after the "/" (e.g. "/24") tells you how
many bits are fixed in the network address - kinda like the "fixed" bit of
a phone number, i.e. the dialling code.

with the 10.0.0.0/8 subnet, only 8 bits are fixed - corresponding to the
first octet ("10"). all the remaining 24 bits (3 octets) are variable, and
therefore available for assigning to individual "hosts" (computers) on
that network. this gives us addresses in the range 10.0.0.0 to
10.255.255.255 (which, according to my calculator, is 4,294,967,296
addresses!)

with the 192.168.0.0/24 subnet, 24 bits are fixed - the first 3 octets,
("192.168.0"). this leaves only the last octet available for assigning
individual addresses - which is 256 addresses, 192.168.0.0 to
192.168.0.255 .

to complicate things a bit further, the first and the last addresses in
the subnet are reserved for the "network address" (the first address, e.g.
192.168.0.0) and the "broadcast address" (the last address, e.g.
192.168.0.255). i'm not going to explain the point of these here though,
but it does mean that a block with 256 addresses, say, only really has 254
addresses available for assigning to hosts.

anyway.....

the alternative to having a separate internet-routable ip address for each
host on your local network is to have one single internet-routable address
for the router or gateway and use one of the reserved subnets for all your
hosts on the local network. then you need software on the router or
gateway to translate local network addresses into your internet-routable
ip address in a way that they can be translated back when packets come in
for that address (and i'm not going to explain this here either!). this is
known as NAT (network address translation).

so then you can add as many hosts to your local network as you like -
without having to obtain internet-routable ip addresses for them - and
they can all communicate with each other using your local net addresses
and with the rest of the internet via NAT on the gateway system.

there are two ways you can allocate addresses on the local network -
dynamically (via dhcp) or statically (by editing the computer's network
config). it's not particularly important which you use, but static config
is probably easiest if you haven't got many hosts and dynamically is
probably easiest if you've got lots.

i don't know anything about the router you mention, but if it can do NAT
and can be configured to have a local net address on the local net side
(as opposed to the internet side), it should be fairly simple to set up
what you want with a mixture of linux and windows and macs and whatever
else you might want to hang off it.

i hope the above makes *some* kind of sense. please feel free to ask for
clarification though!

i'd recommend having a read of some of the documentation on the linux
documentation project's website - in particular the "linux network
administrator's guide": http://www.tldp.org/LDP/nag2/index.html . there's
a lot of useful information on that site, particularly in the HOWTOs - and
some of it's not just useful for linux administration.

will


I can't fault anything you say here, there's a mini mistake here and
there but no matter, but is this not a bit OTT for a newbie who IMHO
is just looking for some basic guidlines?

Any decent router will have a configuration page which only requires a
tiny bit of information to spring into action. Knowing this minumum
information is really all that is required here. So let's make some
suggestions:

1) Give the router the ip address of 192.168.35.1
2) Provide a netmask address of 255.255.255.0
3) Start the DHCP range from 192.168.35.50
4) Give static IP addresses to the Linux/Unix boxes in the range
192.168.35.10 to 192.168.35.49
5) Use the static IP addresses in the range 192.168.35.2 to
192.168.35.9 for printers and perhaps a playstation.
6) If your router is not populated with the DNS server IPs by the ISP
add these in manually.
7) On the Windows PCs, choose DHCP and DNS automattically
8) On the Windows PCs, add the Gateway IP [May not be strictly
necessary, but no harm is done if it is there].
9) On the Linux boxes give fixed IP addresses [a different one for
each machine!] from your fixed range defined in the router.
10) On the Linux boxes, provide the Netmask, DNS IPs and Gateway IP.

Of course, within the router you need to provide a valid userid and
maybe a password, but that's it. No more time wasting reading this
that and the other; just 10 steps to get all your boxes up and running
on the Internet.

For those PCs running Xp, if you open a command window [START RUN
then type in command] and then enter ipconfig /all this will determine
if the PC has all the information it needs. There's similar commands
for other versions of windows and operating systems and maybe someone
else can supply these. A simple test to see if you all is well is
from the command window type; ping www.bbc.co.uk; if it returns the ip
address of 212.58.224.56 then your cooking on gas.

If the above test does not work then ping 192.168.23.1 - it should
return a response that a certain number of bytes have been
transmitted.

If that does not work, then your network has a physical or software
fault or poor configuration at which point you may need some help.

I hope this is of some use and look forward to knowing how you get on.

David Bradley

  #9  
Old August 23rd 04, 12:24 AM posted to uk.telecom.broadband
David Bradley
external usenet poster
 
Posts: 329
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux

On Sun, 22 Aug 2004 22:42:36 GMT, will kemp
wrote:

On Sun, 22 Aug 2004 18:41:23 +0100, David Bradley wrote:

Your internal network should desirably have IP numbers in a "private
range" and these a
10.0.0.0 --- 10.255.255.255
172.16.0.0 --- 172.31.255.255


ah! that's it! i knew there was a third one! ;-)

192.168.0.0 --- 192.168.255.255
There is a strong merit for simple networks to be in the 192.168.y.x
range where 'y' is best chosen between 10 and 253 and 'x' between 2


why do you reckon between 10 and 253 is best?

will


There are a couple of personal reasons for this. So many routers are
left at their default setting of either 0 or 1 that can so easily help
the hacker and the other is that there is less likelyhood of a need to
make a change if, and when, you enter the world of VPNs.

For the word "best" used by me, perhaps say "a worthwhile idea" might
have been better said. I have no wish to upset the purists.

David Bradley

  #10  
Old August 23rd 04, 12:28 AM posted to uk.telecom.broadband
will kemp
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Posts: 67
Default (BT Broadband) home NW newbie, wired ADSL router-modem and Linux

On Sat, 21 Aug 2004 22:53:47 +0100, a.n.other wrote:

I'm not clear how that will work when connected to BT Broadband via my
proposed router. I've read on the web that you can theoretically use DHCP,
and that the router (if smart enough) will automatically get the required
gateway address from the ISP, but this seems to depend on the ISP. Is this
likely to work with BT Broadband and this router?

Or is the gateway address actually something I can, and need to configure
myself in the router? (or a default?). I'd think this is still somewhat
dependent on the ISP though.


there are a few different ways such a network connection could be
configured. one possibility that has been suggested is to give all
computers their own internet-routable ip addresses. this isn't really all
that practical in these days of ip address shortage - and it's not
necessary either, except in certain circumstances (which probably don't
apply to what you're doing).

to understand how this stuff works, you have to first understand the
difference between ip addresses that are routable via the internet and ip
addresses which are only routable locally.

in general, any computer connected to the internet can connect to any
other ip address - the information on how to get from one to the other is
kept by routers along the way. however, there are 3 (if i remember
correctly) blocks of ip addresses which are reserved for local network
use. packets addressed to ip addresses in these blocks should (a) never be
sent out of the local network to the internet and (b) if they do get out
to the internet, should be dropped by the first router they come to and
not passed on.

10.0.0.0/8 and 192.168.0.0/16 are two of these blocks. i' m pretty sure
there's a third one, but can't for the life of me remember what it is.
anyway, 10.0.0.0/8 is generally used as a single subnet (used to be called
a "class 'A'" subnet), with 4,294,967,296 addresses in it. the
192.168.0.0/16 ("class 'B'") block is normally used as 256 "/24" ("class
'C'") subnets (with 256 addresses in each one). the most commonly used
ones would be 192.168.0.0/24 and 192.168.1.0/24 - one or the other of
these is almost always used for local networks like the one you want to
set up.

i realise the above numbers probably look like gobbledygook! in
particular, what on earth are all those "/24" etc bits all about??? well,
to fully understand ip addressing, you need to have a reasonable grasp of
binary - and i'll leave you to find out about that yourself! (if you don't
already know it.)

basically, each of the numbers separated by dots in an ip address (e.g.
192.168.0.27) are 8-bit binary numbers (usually known in this context as
"octets"). an 8-bit binary number can have a (decimal) value from 0 to 255
- in other words, 256 different values.

the part of the network address after the "/" (e.g. "/24") tells you how
many bits are fixed in the network address - kinda like the "fixed" bit of
a phone number, i.e. the dialling code.

with the 10.0.0.0/8 subnet, only 8 bits are fixed - corresponding to the
first octet ("10"). all the remaining 24 bits (3 octets) are variable, and
therefore available for assigning to individual "hosts" (computers) on
that network. this gives us addresses in the range 10.0.0.0 to
10.255.255.255 (which, according to my calculator, is 4,294,967,296
addresses!)

with the 192.168.0.0/24 subnet, 24 bits are fixed - the first 3 octets,
("192.168.0"). this leaves only the last octet available for assigning
individual addresses - which is 256 addresses, 192.168.0.0 to
192.168.0.255 .

to complicate things a bit further, the first and the last addresses in
the subnet are reserved for the "network address" (the first address, e.g.
192.168.0.0) and the "broadcast address" (the last address, e.g.
192.168.0.255). i'm not going to explain the point of these here though,
but it does mean that a block with 256 addresses, say, only really has 254
addresses available for assigning to hosts.

anyway.....

the alternative to having a separate internet-routable ip address for each
host on your local network is to have one single internet-routable address
for the router or gateway and use one of the reserved subnets for all your
hosts on the local network. then you need software on the router or
gateway to translate local network addresses into your internet-routable
ip address in a way that they can be translated back when packets come in
for that address (and i'm not going to explain this here either!). this is
known as NAT (network address translation).

so then you can add as many hosts to your local network as you like -
without having to obtain internet-routable ip addresses for them - and
they can all communicate with each other using your local net addresses
and with the rest of the internet via NAT on the gateway system.

there are two ways you can allocate addresses on the local network -
dynamically (via dhcp) or statically (by editing the computer's network
config). it's not particularly important which you use, but static config
is probably easiest if you haven't got many hosts and dynamically is
probably easiest if you've got lots.

i don't know anything about the router you mention, but if it can do NAT
and can be configured to have a local net address on the local net side
(as opposed to the internet side), it should be fairly simple to set up
what you want with a mixture of linux and windows and macs and whatever
else you might want to hang off it.

i hope the above makes *some* kind of sense. please feel free to ask for
clarification though!

i'd recommend having a read of some of the documentation on the linux
documentation project's website - in particular the "linux network
administrator's guide": http://www.tldp.org/LDP/nag2/index.html . there's
a lot of useful information on that site, particularly in the HOWTOs - and
some of it's not just useful for linux administration.

will

 




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