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Old 06-08-2011, 11:54 PM
Timothy Murphy
 
Default Some questions on networking gateways

Apologies if you saw this before;
I posted it in the wrong newsgroup.

I have a home LAN on network 192.168.2.0,
with a server at 192.168.2.2,
and various other laptops, iphones, etc on the LAN,
eg I am currently on laptop 192.168.2.7 .

There seem to be 3 places where gateways are specified:

1. In /etc/dhcpd.conf on the server, under "option routers";

2. In /etc/sysconfig/network-scripts/ifcfg-*
on the client machines;

3. In /etc/network on these machines.

I've read that the entries in ifcfg-* are ignored?

I haven't actually given gateways in /etc/network anywhere.
Perhaps I should?

My server has address 192.168.2.2 on eth1,
and address 192.168.1.2 on eth0, which is
connected to my ADSL modem with address 192.168.1.254 .

Now I'm wondering if I should give
GATEWAY=192.168.2.2 or GATEWAY=192.168.1.254
on client machines?

route -n on the server gives
------------------------------
Destination Gateway Genmask Flags Metric Ref Use
Iface
192.168.5.2 0.0.0.0 255.255.255.255 UH 0 0 0 tun0
192.168.5.0 192.168.5.2 255.255.255.0 UG 0 0 0 tun0
192.168.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1
0.0.0.0 192.168.1.254 0.0.0.0 UG 0 0 0 eth0
------------------------------
I'm not sure how it found the (correct) default gateway 192.168.1.254 ?

These questions arise because I tried changing my server
to machine 192.168.1.5, connected to the modem.
Everything worked fine on the new server,
but I could not access the ethernet on other machines,
even after modifying the route tables on these machines
to have default gateway 192.168.2.5 (the new server).

I tried both with NetworkManager and with the network service,
but neither worked satisfactorily.

I'm running shorewall, but there is no mention of 192.168.1.254 there.

Any enlightenment gratefully received.

--
Timothy Murphy
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland

--
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Old 06-09-2011, 01:47 PM
Tim
 
Default Some questions on networking gateways

On Thu, 2011-06-09 at 00:54 +0100, Timothy Murphy wrote:
> I have a home LAN on network 192.168.2.0,
> with a server at 192.168.2.2,
> and various other laptops, iphones, etc on the LAN,
> eg I am currently on laptop 192.168.2.7 .
>
> There seem to be 3 places where gateways are specified:
>
> 1. In /etc/dhcpd.conf on the server, under "option routers";
>
> 2. In /etc/sysconfig/network-scripts/ifcfg-*
> on the client machines;
>
> 3. In /etc/network on these machines.

If you *don't* configure a gateway address on the clients, then the DHCP
server can supply them with the information. If you do configure a
gateway on the clients, then it can override a DHCP supplied address.

> My server has address 192.168.2.2 on eth1,
> and address 192.168.1.2 on eth0, which is
> connected to my ADSL modem with address 192.168.1.254 .
>
> Now I'm wondering if I should give
> GATEWAY=192.168.2.2 or GATEWAY=192.168.1.254
> on client machines?

Which port do they connect to? If they're on the same network as eth1
(192.168.2.2), then that's their gateway (the address they go /through/
to get elsewhere).

A client's gateway is the thing *they* have to go through, to get
outside. It's the bit in-between one network and another, hence the
nickname.

And the gateway for 192.168.2.2. is 192.168.1.254.

> route -n on the server gives
> ------------------------------
> Destination Gateway Genmask Flags Metric Ref Use Iface
> 192.168.5.2 0.0.0.0 255.255.255.255 UH 0 0 0 tun0
> 192.168.5.0 192.168.5.2 255.255.255.0 UG 0 0 0 tun0
> 192.168.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
> 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
> 169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth1
> 0.0.0.0 192.168.1.254 0.0.0.0 UG 0 0 0 eth0
> ------------------------------
> I'm not sure how it found the (correct) default gateway 192.168.1.254 ?

Is it old information, still kept? Or is it recently discovered?

If it's recently discovered, is your network actually set up as you
think it is. If you have something else with its own DHCP server doling
out information, it can clash. Having two DHCP servers on a LAN can be
a real problem.

> These questions arise because I tried changing my server
> to machine 192.168.1.5, connected to the modem.
> Everything worked fine on the new server,
> but I could not access the ethernet on other machines,
> even after modifying the route tables on these machines
> to have default gateway 192.168.2.5 (the new server).
>
> I tried both with NetworkManager and with the network service,
> but neither worked satisfactorily.
>
> I'm running shorewall, but there is no mention of 192.168.1.254 there.
>
> Any enlightenment gratefully received.

You've checked that your new gateway isn't firewalling off your LAN?
That your gateway has IP-forwaring set?

--
[tim@localhost ~]$ uname -r
2.6.27.25-78.2.56.fc9.i686

Don't send private replies to my address, the mailbox is ignored. I
read messages from the public lists.



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Old 06-09-2011, 10:46 PM
Timothy Murphy
 
Default Some questions on networking gateways

Tim wrote:

> You've checked that your new gateway isn't firewalling off your LAN?
> That your gateway has IP-forwaring set?

Thanks for all your advice.
I'll study it carefully.

--
Timothy Murphy
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland

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Old 06-11-2011, 11:56 AM
Timothy Murphy
 
Default Some questions on networking gateways

Timothy Murphy wrote:

> Tim wrote:
>
>> You've checked that your new gateway isn't firewalling off your LAN?
>> That your gateway has IP-forwaring set?
>
> Thanks for all your advice.
> I'll study it carefully.

Someone (maybe it was personal email) thought I was being snide
in this response.
Not so; I always find "Tim"s advice useful and helpful.

However, in this case I was departing that day for a 2 month visit
to a far country (Italy), and had to decide whether to leave my home system
in the possibly sick state it was currently in
(the partition table on the server having been destroyed,
and re-built on theoretical grounds),
or change servers before leaving.
I decided on the former, the server having worked without re-booting
(the point at which my theoretical calculation would be put to the test)
for 6 months, so the probability it will continue for 2 more is quite high.
I hope.


--
Timothy Murphy
e-mail: gayleard /at/ eircom.net
tel: +353-86-2336090, +353-1-2842366
s-mail: School of Mathematics, Trinity College, Dublin 2, Ireland

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