Pinging machines on different subnets

Hi,
I have a question about cable modem networking and Linux. I have 3
machines, 2 windows XP and a Debian Linux. I use the linux box as a
server and they all get assigned IP address via the cable systems
DHCP. This week the lease on the IP that the Linux box had expired and
it got a new IP, one that was out of the subnet of the Windows boxes.
Now these machine can't ping each other anymore (i.e, the windows
machines can ping each other but cant see the L-Box, and the L-box
cant see them). ALL machines can ping other internet address, and
other addresses in the same subnet. Friends of mine (on other IPSs)
are able to ping ALL my machines.

So, how do I get the L-Box to be reachable from the Win-boxes, and why
cant I do a cross-subnet ping?

Example (not the real addresses):
Win machine A: IP=24.155.82.154 Subnet Mask=255.255.240.0
Win machine B: IP=24.155.93.215 Subnet Mask=255.255.240.0
Linux machine: IP=24.59.233.99 Subnet Mask=255.255.254.0

TIA,
Chris

On 11 Nov 2003 14:01:20 -0800, Chris <(E-Mail Removed)> wrote:
> Hi,
> I have a question about cable modem networking and Linux. I have 3
> machines, 2 windows XP and a Debian Linux. I use the linux box as a
> server and they all get assigned IP address via the cable systems
> DHCP. This week the lease on the IP that the Linux box had expired and
> it got a new IP, one that was out of the subnet of the Windows boxes.
> Now these machine can't ping each other anymore (i.e, the windows
> machines can ping each other but cant see the L-Box, and the L-box
> cant see them). ALL machines can ping other internet address, and
> other addresses in the same subnet. Friends of mine (on other IPSs)
> are able to ping ALL my machines.
>
> So, how do I get the L-Box to be reachable from the Win-boxes, and why
> cant I do a cross-subnet ping?
>
> Example (not the real addresses):
> Win machine A: IP=24.155.82.154 Subnet Mask=255.255.240.0
> Win machine B: IP=24.155.93.215 Subnet Mask=255.255.240.0
> Linux machine: IP=24.59.233.99 Subnet Mask=255.255.254.0

Do these all use same default gw? Maybe it does not respond because both
subnets are on same interface. You could add -net routes for the opposite
subnet. This would be easy for the Linux box:

route add -net 24.155.80.0 netmask 255.255.240.0 dev eth0

But for adding local route for net 24.59.232.0 netmask 255.255.254.0
to Windows to communicate back the other way, you are on your own.

--
David Efflandt - All spam ignored http://www.de-srv.com/
http://www.autox.chicago.il.us/ http://www.berniesfloral.net/
http://cgi-help.virtualave.net/ http://hammer.prohosting.com/~cgi-wiz/

Chris,

Typically you would need a router to reach other subnets.

Your friends were able to ping your machines because their traffic is going
through the ISP's routers since the traffic they're pinging isn't on their
subnet.

I haven't done this yet but plan to in the future. I may be incorrect but I
think you can create your own linux router with the existing linux box you
have. Since it's the one already connected to your ISP you're half way there.
You need to add another ethernet card to your box. This card connects to your
Windows subnet. I'm no expert by any stretch of the imagination but you can set
iptables up so that traffic can be routed between the 2 ethernet cards thus
access to both subnets. I think is called IP forwarding.The only downside is
you would need to change the IP address of the card connected to the ISP's
subnet whenever that IP changes. I think you have to do that already whenever
the IP changes.

There are resources around that tell you how. I don't know if these links are
good or not but I got them from a document called Installing a Linux
Firewall/Router. I can't remember where I got this document but check
linux.org/docs to see if there's any info.

Home Network Mini How-To :
http://www.linux.org/docs/ldp/howto/...ini-HOWTO.html

NAT How-To : http://www.netfilter.org/documentati...NAT-HOWTO.html

Linux IP Masquerade How-To: http://ipmasq.cjb.net/

You can also search google for linux router how-tos. You may be able to find
info on iptables which may guide you in setting this up.

A good tutorial on iptables is the iptables tutorial by Oskar Andreasson. You
can find it at http://iptables-tutorial.frozentux.n...-tutorial.html.
There's a good list of links and resources in appendix D.


Bill in Sacramento, California....

(E-Mail Removed) (David Efflandt) wrote in message news:<(E-Mail Removed)>...
> On 11 Nov 2003 14:01:20 -0800, Chris <(E-Mail Removed)> wrote:
> > Hi,
> > I have a question about cable modem networking and Linux. I have 3
> > machines, 2 windows XP and a Debian Linux. I use the linux box as a
> > server and they all get assigned IP address via the cable systems
> > DHCP. This week the lease on the IP that the Linux box had expired and
> > it got a new IP, one that was out of the subnet of the Windows boxes.
> > Now these machine can't ping each other anymore (i.e, the windows
> > machines can ping each other but cant see the L-Box, and the L-box
> > cant see them). ALL machines can ping other internet address, and
> > other addresses in the same subnet. Friends of mine (on other IPSs)
> > are able to ping ALL my machines.
> >
> > So, how do I get the L-Box to be reachable from the Win-boxes, and why
> > cant I do a cross-subnet ping?
> >
> > Example (not the real addresses):
> > Win machine A: IP=24.155.82.154 Subnet Mask=255.255.240.0
> > Win machine B: IP=24.155.93.215 Subnet Mask=255.255.240.0
> > Linux machine: IP=24.59.233.99 Subnet Mask=255.255.254.0
>
> Do these all use same default gw? Maybe it does not respond because both
> subnets are on same interface. You could add -net routes for the opposite
> subnet. This would be easy for the Linux box:
>
> route add -net 24.155.80.0 netmask 255.255.240.0 dev eth0
>
> But for adding local route for net 24.59.232.0 netmask 255.255.254.0
> to Windows to communicate back the other way, you are on your own.

Sorry, gw? Dont really know what you mean there. Still, I will try the
net routes thing and let you know. What do you mean by 'both subnets
are on the same interface? Does this have to do with me, or the cable
company?

Thanks again
Chris

On 12 Nov 2003 05:52:54 -0800, Chris <(E-Mail Removed)> wrote:
> (E-Mail Removed) (David Efflandt) wrote in message news:<(E-Mail Removed)>...
>> On 11 Nov 2003 14:01:20 -0800, Chris <(E-Mail Removed)> wrote:
>> > Hi,
>> > I have a question about cable modem networking and Linux. I have 3
>> > machines, 2 windows XP and a Debian Linux. I use the linux box as a
>> > server and they all get assigned IP address via the cable systems
>> > DHCP. This week the lease on the IP that the Linux box had expired and
>> > it got a new IP, one that was out of the subnet of the Windows boxes.
>> > Now these machine can't ping each other anymore (i.e, the windows
>> > machines can ping each other but cant see the L-Box, and the L-box
>> > cant see them). ALL machines can ping other internet address, and
>> > other addresses in the same subnet. Friends of mine (on other IPSs)
>> > are able to ping ALL my machines.
>> >
>> > So, how do I get the L-Box to be reachable from the Win-boxes, and why
>> > cant I do a cross-subnet ping?
>> >
>> > Example (not the real addresses):
>> > Win machine A: IP=24.155.82.154 Subnet Mask=255.255.240.0
>> > Win machine B: IP=24.155.93.215 Subnet Mask=255.255.240.0
>> > Linux machine: IP=24.59.233.99 Subnet Mask=255.255.254.0
>>
>> Do these all use same default gw? Maybe it does not respond because both
>> subnets are on same interface. You could add -net routes for the opposite
>> subnet. This would be easy for the Linux box:
>>
>> route add -net 24.155.80.0 netmask 255.255.240.0 dev eth0
>>
>> But for adding local route for net 24.59.232.0 netmask 255.255.254.0
>> to Windows to communicate back the other way, you are on your own.
>
> Sorry, gw? Dont really know what you mean there. Still, I will try the
> net routes thing and let you know. What do you mean by 'both subnets
> are on the same interface? Does this have to do with me, or the cable
> company?

gw is gateway (next hop to reach a non-local network). It usually does
not bounce something back the way it came in. So you need to do local
routing (no gateway) so your different networks can find themselves by arp
broadcasting instead of to a gateway.

24.155.82.154------|
24.155.93.215------|------(gateway IP)ISP's-ROUTER-------internet
24.59.233.99-------|

So going from 24.155.93.215 to 24.59.233.99 needs to route locally, even
though different subnets, instead of via the gateway/router.

--
David Efflandt - All spam ignored http://www.de-srv.com/
http://www.autox.chicago.il.us/ http://www.berniesfloral.net/
http://cgi-help.virtualave.net/ http://hammer.prohosting.com/~cgi-wiz/

(E-Mail Removed) (David Efflandt) wrote in message news:<(E-Mail Removed)>...
> On 12 Nov 2003 05:52:54 -0800, Chris <(E-Mail Removed)> wrote:
> > (E-Mail Removed) (David Efflandt) wrote in message news:<(E-Mail Removed)>...
> >> On 11 Nov 2003 14:01:20 -0800, Chris <(E-Mail Removed)> wrote:
> >> > Hi,
> >> > I have a question about cable modem networking and Linux. I have 3
> >> > machines, 2 windows XP and a Debian Linux. I use the linux box as a
> >> > server and they all get assigned IP address via the cable systems
> >> > DHCP. This week the lease on the IP that the Linux box had expired and
> >> > it got a new IP, one that was out of the subnet of the Windows boxes.
> >> > Now these machine can't ping each other anymore (i.e, the windows
> >> > machines can ping each other but cant see the L-Box, and the L-box
> >> > cant see them). ALL machines can ping other internet address, and
> >> > other addresses in the same subnet. Friends of mine (on other IPSs)
> >> > are able to ping ALL my machines.
> >> >
> >> > So, how do I get the L-Box to be reachable from the Win-boxes, and why
> >> > cant I do a cross-subnet ping?
> >> >
> >> > Example (not the real addresses):
> >> > Win machine A: IP=24.155.82.154 Subnet Mask=255.255.240.0
> >> > Win machine B: IP=24.155.93.215 Subnet Mask=255.255.240.0
> >> > Linux machine: IP=24.59.233.99 Subnet Mask=255.255.254.0
> >>
> >> Do these all use same default gw? Maybe it does not respond because both
> >> subnets are on same interface. You could add -net routes for the opposite
> >> subnet. This would be easy for the Linux box:
> >>
> >> route add -net 24.155.80.0 netmask 255.255.240.0 dev eth0
> >>
> >> But for adding local route for net 24.59.232.0 netmask 255.255.254.0
> >> to Windows to communicate back the other way, you are on your own.
> >
> > Sorry, gw? Dont really know what you mean there. Still, I will try the
> > net routes thing and let you know. What do you mean by 'both subnets
> > are on the same interface? Does this have to do with me, or the cable
> > company?
>
> gw is gateway (next hop to reach a non-local network). It usually does
> not bounce something back the way it came in. So you need to do local
> routing (no gateway) so your different networks can find themselves by arp
> broadcasting instead of to a gateway.
>
> 24.155.82.154------|
> 24.155.93.215------|------(gateway IP)ISP's-ROUTER-------internet
> 24.59.233.99-------|
>
> So going from 24.155.93.215 to 24.59.233.99 needs to route locally, even
> though different subnets, instead of via the gateway/router.

Oh, right...gateway. No, I dont believe they have the same GW. The 2
Win-boxes have the same GW, that I know. I will check and confirm if
the Linux box does, but I think not. If they did have different GWs,
would I still have to setup a local route? Or should that work as
normal? I guess what I dont get is why traffic from one subnet (using
one GW) cant get to another subnet (with another GW). From your
diagram, it would seem that I can only see machines that are 'inside'
the GW (again, I will check on the L-box's GW).

Thanks for help.

(E-Mail Removed) (Chris) wrote in message news:<(E-Mail Removed). com>...
> (E-Mail Removed) (David Efflandt) wrote in message news:<(E-Mail Removed)>...
> > On 12 Nov 2003 05:52:54 -0800, Chris <(E-Mail Removed)> wrote:
> > > (E-Mail Removed) (David Efflandt) wrote in message news:<(E-Mail Removed)>...
> > >> On 11 Nov 2003 14:01:20 -0800, Chris <(E-Mail Removed)> wrote:
> > >> > Hi,
> > >> > I have a question about cable modem networking and Linux. I have 3
> > >> > machines, 2 windows XP and a Debian Linux. I use the linux box as a
> > >> > server and they all get assigned IP address via the cable systems
> > >> > DHCP. This week the lease on the IP that the Linux box had expired and
> > >> > it got a new IP, one that was out of the subnet of the Windows boxes.
> > >> > Now these machine can't ping each other anymore (i.e, the windows
> > >> > machines can ping each other but cant see the L-Box, and the L-box
> > >> > cant see them). ALL machines can ping other internet address, and
> > >> > other addresses in the same subnet. Friends of mine (on other IPSs)
> > >> > are able to ping ALL my machines.
> > >> >
> > >> > So, how do I get the L-Box to be reachable from the Win-boxes, and why
> > >> > cant I do a cross-subnet ping?
> > >> >
> > >> > Example (not the real addresses):
> > >> > Win machine A: IP=24.155.82.154 Subnet Mask=255.255.240.0
> > >> > Win machine B: IP=24.155.93.215 Subnet Mask=255.255.240.0
> > >> > Linux machine: IP=24.59.233.99 Subnet Mask=255.255.254.0
> > >>
> > >> Do these all use same default gw? Maybe it does not respond because both
> > >> subnets are on same interface. You could add -net routes for the opposite
> > >> subnet. This would be easy for the Linux box:
> > >>
> > >> route add -net 24.155.80.0 netmask 255.255.240.0 dev eth0
> > >>
> > >> But for adding local route for net 24.59.232.0 netmask 255.255.254.0
> > >> to Windows to communicate back the other way, you are on your own.
> > >
> > > Sorry, gw? Dont really know what you mean there. Still, I will try the
> > > net routes thing and let you know. What do you mean by 'both subnets
> > > are on the same interface? Does this have to do with me, or the cable
> > > company?
> >
> > gw is gateway (next hop to reach a non-local network). It usually does
> > not bounce something back the way it came in. So you need to do local
> > routing (no gateway) so your different networks can find themselves by arp
> > broadcasting instead of to a gateway.
> >
> > 24.155.82.154------|
> > 24.155.93.215------|------(gateway IP)ISP's-ROUTER-------internet
> > 24.59.233.99-------|
> >
> > So going from 24.155.93.215 to 24.59.233.99 needs to route locally, even
> > though different subnets, instead of via the gateway/router.
>
> Oh, right...gateway. No, I dont believe they have the same GW. The 2
> Win-boxes have the same GW, that I know. I will check and confirm if
> the Linux box does, but I think not. If they did have different GWs,
> would I still have to setup a local route? Or should that work as
> normal? I guess what I dont get is why traffic from one subnet (using
> one GW) cant get to another subnet (with another GW). From your
> diagram, it would seem that I can only see machines that are 'inside'
> the GW (again, I will check on the L-box's GW).
>
> Thanks for help.

OK...I did the route add thing, but that machine (24.59.233.99) still
cannot ping the 24.155.93.215 machine. Does it HAVE to be setup on
both ends for a simple ping to work? Also, I can confirm that the
L-box does not have the same gateway as the Win-boxes. Any ideas?

I have heard of the process of making an IP alias, but dont know
really what that is or whats involved. Thoughts?

Thanks guys.