Two Routers, One NAT

26 Dec 2006 12:03 PM

Nipi

I would like to share this experience and ask one question about one
home network configuration.
I have two routers at home, one provided by the ISP, not wireless,
which I will call router "A"
and another wireless one i recently got for the laptop, I will call it
router "B"
The router A is connected directly to the ISP and there are two
computers connected to the internet through it. And since I can't
connect the router B to the ISP cable directly (their decision) I first
connected the WAN port of router B to one LAN port of router A, which
allowed my laptop to access the internet but i didn't like it that way
because this had to put the laptop behind two NATs.
So i thought of another configuration, to use the router B like a
"wireless HUB only" by connecting one of its LAN ports (instead of the
WAN port) to the router A, which I figured would make the laptop able
to access the ISP's router A directly.
Here came the problem, I noticed that not only the laptop (which is
connected directly to router B) is taking an IP address from the router
B's DHCP, but also the two computers which are connected to the router
A!, and of course this made them all unable to access the internet,
because router B has nothing on the WAN port.
I could solve this problem with one of two methods, either force all
the computers to take IPs from router A, by specifying fixed IPs within
router A's range and use its IP as default gateway, or by completely
disabling the DHCP service on router B, which is a better idea since i
don't need it if i'm using it only like a HUB.
But my question is, what made all the computers including those
connected directly to router A, to connect and take IPs only from the
router B, and on what does it depend that a computer chooses one router
if more than one are on the same network?
(All the computers are running windows XP)

26 Dec 2006 3:14 PM

David Hettel

Your second configuration is not a valid configuration. You can not simply
connect two routers lan ports together and expect it to work. What you need
to do is disable both DHCP and NAT on router B. Not knowing the brand or
model of router B I would advise you to goggle on router B model number and
disable DHCP.

--
David Hettel

Please post any reply as a follow-up message in the news group for everyone
to see. I'm sorry, but I don't answer questions addressed directly to me in
E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com

DISCLAIMER: This posting is provided "AS IS" with no warranty of any kind,
either expressed or implied, made in relation to the accuracy, reliability
or content of this post. The author shall not be liable for any direct,
indirect, incidental or consequential damages arising out of the use of, or
inability to use, information or opinions expressed in this post and confers
no rights.

Show quoteHide quote

"Nipi" <yame***@gmail.com> wrote in message
news:1167134615.790613.283590@a3g2000cwd.googlegroups.com...
>I would like to share this experience and ask one question about one
> home network configuration.
> I have two routers at home, one provided by the ISP, not wireless,
> which I will call router "A"
> and another wireless one i recently got for the laptop, I will call it
> router "B"
> The router A is connected directly to the ISP and there are two
> computers connected to the internet through it. And since I can't
> connect the router B to the ISP cable directly (their decision) I first
> connected the WAN port of router B to one LAN port of router A, which
> allowed my laptop to access the internet but i didn't like it that way
> because this had to put the laptop behind two NATs.
> So i thought of another configuration, to use the router B like a
> "wireless HUB only" by connecting one of its LAN ports (instead of the
> WAN port) to the router A, which I figured would make the laptop able
> to access the ISP's router A directly.
> Here came the problem, I noticed that not only the laptop (which is
> connected directly to router B) is taking an IP address from the router
> B's DHCP, but also the two computers which are connected to the router
> A!, and of course this made them all unable to access the internet,
> because router B has nothing on the WAN port.
> I could solve this problem with one of two methods, either force all
> the computers to take IPs from router A, by specifying fixed IPs within
> router A's range and use its IP as default gateway, or by completely
> disabling the DHCP service on router B, which is a better idea since i
> don't need it if i'm using it only like a HUB.
> But my question is, what made all the computers including those
> connected directly to router A, to connect and take IPs only from the
> router B, and on what does it depend that a computer chooses one router
> if more than one are on the same network?
> (All the computers are running windows XP)
>

26 Dec 2006 7:38 PM

Nipi

Didn't i say that i disabled the DHCP, and that it's working fine now,
my only question was not how to make it work but why the router B is
only gives IP, but I got my answer i think because most posts said one
thing, that it has to do only with the speed of response.

David Hettel wrote:
Show quoteHide quote

> Your second configuration is not a valid configuration. You can not simply
> connect two routers lan ports together and expect it to work. What you need
> to do is disable both DHCP and NAT on router B. Not knowing the brand or
> model of router B I would advise you to goggle on router B model number and
> disable DHCP.
>
> --
> David Hettel
>
> Please post any reply as a follow-up message in the news group for everyone
> to see. I'm sorry, but I don't answer questions addressed directly to me in
> E-mail or news groups.
>
> Microsoft Most Valuable Professional Program
> http://mvp.support.microsoft.com
>
> DISCLAIMER: This posting is provided "AS IS" with no warranty of any kind,
> either expressed or implied, made in relation to the accuracy, reliability
> or content of this post. The author shall not be liable for any direct,
> indirect, incidental or consequential damages arising out of the use of, or
> inability to use, information or opinions expressed in this post and confers
> no rights.
>
>
>
> "Nipi" <yame***@gmail.com> wrote in message
> news:1167134615.790613.283590@a3g2000cwd.googlegroups.com...
> >I would like to share this experience and ask one question about one
> > home network configuration.
> > I have two routers at home, one provided by the ISP, not wireless,
> > which I will call router "A"
> > and another wireless one i recently got for the laptop, I will call it
> > router "B"
> > The router A is connected directly to the ISP and there are two
> > computers connected to the internet through it. And since I can't
> > connect the router B to the ISP cable directly (their decision) I first
> > connected the WAN port of router B to one LAN port of router A, which
> > allowed my laptop to access the internet but i didn't like it that way
> > because this had to put the laptop behind two NATs.
> > So i thought of another configuration, to use the router B like a
> > "wireless HUB only" by connecting one of its LAN ports (instead of the
> > WAN port) to the router A, which I figured would make the laptop able
> > to access the ISP's router A directly.
> > Here came the problem, I noticed that not only the laptop (which is
> > connected directly to router B) is taking an IP address from the router
> > B's DHCP, but also the two computers which are connected to the router
> > A!, and of course this made them all unable to access the internet,
> > because router B has nothing on the WAN port.
> > I could solve this problem with one of two methods, either force all
> > the computers to take IPs from router A, by specifying fixed IPs within
> > router A's range and use its IP as default gateway, or by completely
> > disabling the DHCP service on router B, which is a better idea since i
> > don't need it if i'm using it only like a HUB.
> > But my question is, what made all the computers including those
> > connected directly to router A, to connect and take IPs only from the
> > router B, and on what does it depend that a computer chooses one router
> > if more than one are on the same network?
> > (All the computers are running windows XP)
> >

26 Dec 2006 4:36 PM

Doug Sherman [MVP]

It's a race and the results are unpredictable. DHCP clients use broadcast
packets to request an IP address. In your case router B happened to be the
first to respond.

Doug Sherman
MCSE, MCSA, MCP+I, MVP

Show quoteHide quote

"Nipi" <yame***@gmail.com> wrote in message
news:1167134615.790613.283590@a3g2000cwd.googlegroups.com...
> I would like to share this experience and ask one question about one
> home network configuration.
> I have two routers at home, one provided by the ISP, not wireless,
> which I will call router "A"
> and another wireless one i recently got for the laptop, I will call it
> router "B"
> The router A is connected directly to the ISP and there are two
> computers connected to the internet through it. And since I can't
> connect the router B to the ISP cable directly (their decision) I first
> connected the WAN port of router B to one LAN port of router A, which
> allowed my laptop to access the internet but i didn't like it that way
> because this had to put the laptop behind two NATs.
> So i thought of another configuration, to use the router B like a
> "wireless HUB only" by connecting one of its LAN ports (instead of the
> WAN port) to the router A, which I figured would make the laptop able
> to access the ISP's router A directly.
> Here came the problem, I noticed that not only the laptop (which is
> connected directly to router B) is taking an IP address from the router
> B's DHCP, but also the two computers which are connected to the router
> A!, and of course this made them all unable to access the internet,
> because router B has nothing on the WAN port.
> I could solve this problem with one of two methods, either force all
> the computers to take IPs from router A, by specifying fixed IPs within
> router A's range and use its IP as default gateway, or by completely
> disabling the DHCP service on router B, which is a better idea since i
> don't need it if i'm using it only like a HUB.
> But my question is, what made all the computers including those
> connected directly to router A, to connect and take IPs only from the
> router B, and on what does it depend that a computer chooses one router
> if more than one are on the same network?
> (All the computers are running windows XP)
>

26 Dec 2006 5:13 PM

Jack (MVP-Networking).

Hi
Hopefully you make sure that the Core IP of the second Router is on the same
subnet as the first Router.
Wireless Router as a Switch with an Access Point -
http://www.ezlan.net/router_AP.html
Wireless Router are actually small computers with cup. OS (firmware) and
memory.
So it depending on the core speed of the device and what residual info is
still in memory that would cause one unit to kick up first.
Jack (MVP-Networking).

Show quoteHide quote

"Nipi" <yame***@gmail.com> wrote in message
news:1167134615.790613.283590@a3g2000cwd.googlegroups.com...
>I would like to share this experience and ask one question about one
> home network configuration.
> I have two routers at home, one provided by the ISP, not wireless,
> which I will call router "A"
> and another wireless one i recently got for the laptop, I will call it
> router "B"
> The router A is connected directly to the ISP and there are two
> computers connected to the internet through it. And since I can't
> connect the router B to the ISP cable directly (their decision) I first
> connected the WAN port of router B to one LAN port of router A, which
> allowed my laptop to access the internet but i didn't like it that way
> because this had to put the laptop behind two NATs.
> So i thought of another configuration, to use the router B like a
> "wireless HUB only" by connecting one of its LAN ports (instead of the
> WAN port) to the router A, which I figured would make the laptop able
> to access the ISP's router A directly.
> Here came the problem, I noticed that not only the laptop (which is
> connected directly to router B) is taking an IP address from the router
> B's DHCP, but also the two computers which are connected to the router
> A!, and of course this made them all unable to access the internet,
> because router B has nothing on the WAN port.
> I could solve this problem with one of two methods, either force all
> the computers to take IPs from router A, by specifying fixed IPs within
> router A's range and use its IP as default gateway, or by completely
> disabling the DHCP service on router B, which is a better idea since i
> don't need it if i'm using it only like a HUB.
> But my question is, what made all the computers including those
> connected directly to router A, to connect and take IPs only from the
> router B, and on what does it depend that a computer chooses one router
> if more than one are on the same network?
> (All the computers are running windows XP)
>

26 Dec 2006 8:32 PM

Nipi

Jack (MVP-Networking). wrote:

> Hi
> Hopefully you make sure that the Core IP of the second Router is on the same
> subnet as the first Router.
> Wireless Router as a Switch with an Access Point -
> http://www.ezlan.net/router_AP.html
> Wireless Router are actually small computers with cup. OS (firmware) and
> memory.
> So it depending on the core speed of the device and what residual info is
> still in memory that would cause one unit to kick up first.
> Jack (MVP-Networking).

The article describes exactly what i went through, however there is one
thing that isn't correct at least in my case.
The article says that i will need a crossover cable if i connect the
routers using two LAN ports, and a normal (straight patch) cable if
one port is uplink, but i used the same cable (normal one) in both
cases and it worked.

In addition to that, I have one question, you mentioned and the article
as well, that the router B which is used as a switch, should have an IP
of the same subnet as the main router, why?
My second router has a completely different IP (192.168.2.1) while the
first is (192.168.0.254) and everything is working, except that i can't
access the router B to configure it if needed, so unless if this is the
only reason why that's needed, i don't see a point.

26 Dec 2006 10:30 PM

John Wunderlich

"Nipi" <yame***@gmail.com> wrote in
news:1167165174.788108.311080@48g2000cwx.googlegroups.com:

> The article describes exactly what i went through, however there
> is one thing that isn't correct at least in my case.
> The article says that i will need a crossover cable if i connect
> the routers using two LAN ports, and a normal (straight patch)
> cable if one port is uplink, but i used the same cable (normal
> one) in both cases and it worked.

Time marches on. The "correct" way is as stated in the article.
Manufacturer's found the problem of cross vs non-cross cabling was
confusing and they devised a way for their hardware to auto-sense the
connection and internally agree on an in-out configuration -- so with
newer equipment, the correct cabling isn't really necessary. But
giving out advice that cross-cabling doesn't matter would be bad for
people with older equipment.

> In addition to that, I have one question, you mentioned and the
> article as well, that the router B which is used as a switch,
> should have an IP of the same subnet as the main router, why?
> My second router has a completely different IP (192.168.2.1) while
> the first is (192.168.0.254) and everything is working, except
> that i can't access the router B to configure it if needed, so
> unless if this is the only reason why that's needed, i don't see a
> point.

Once again, this is to ensure that it works. When router B receives
a packet on one of its LAN ports destined for a subnet that is not
its own subnet, it has every right to direct it solely to the WAN
port (even if it's unconnected) and not on the LAN ports. In
practice, though, the packet is broadcast locally as well and for
this reason, it happens to work.
As you point out, putting the second router on the same subnet will
allow you to access its configuration from any device.

The point that you don't see is that much of the advice you get is
generic in the respect that the advice is in regard to how networks
are designed to work... that some manufacturers loosen things up so
some things work when they shouldn't (and thus avoid complaints) is
great if it works for you but could cause unpredictable side effects
later. I prefer not to bank on loopholes.

Good Luck,
John