Problems setting up DNS, gateway und subnetmask!

Following up on Old guy's post, the other available address
(81.10.53.21) must be a machine that has the routing information to
your gateway otherwise you are stuck.

If you can ping that address, then find out from you ISP that is the
gateway for your network segment and if not they need to give you the
correct configuration or they need to verify the information you have.
It is possible you may have have a typographical error ('typo').

On Wed, 28 Dec 2005 01:10:04 +0100, Tamer Higazi <no.TakeThisOut@email.de> wrote:

> Hi!
> I have received from my ISP an IP, DNS, Subnetmask and the DNS
> Serverentries to add to my ubuntu linux machine
>
> My interfaces File /etc/network/interfaces:
[...]
> auto eth0
>
> iface eth0 inet static
> address 81.10.53.22
> netmask 255.255.255.252
> gateway 10.0.0.138
> dns-search lan
> dns-nameservers 163.121.128.134 212.103.160.18
>
> My File /etc/hosts:
>
> 127.0.0.1 localhost.localdomain localhost ubuntu
> # The following lines are desirable for IPv6 capable hosts
> fe00::0 ip6-localnet
> ff00::0 ip6-mcastprefix
> ff02::1 ip6-allnodes
> ff02::2 ip6-allrouters
> ff02::3 ip6-allhosts
>
> If I enter the command route:
>
> Kernel IP Routentabelle
> Ziel Router Genmask Flags Metric Ref Use Iface
> 81.10.53.20 * 255.255.255.252 U 0 0 0 eth0
>
> If I run explicitly this command to add the gateway to my eth0 interface:
>
>
> sudo route add default gateway 10.0.0.138 eth0
>
> I receive this errormessage:
> SIOCADDRT: Das Netzwerk ist nicht erreichbar (Network unreachable)

How come that you have a routable address for the linux machine, but
a non-routable gateway address?

Given the IP and mask of the card, it should be on a network
comprising the four addresses

81.10.53.20
81.10.53.21
81.10.53.22
81.10.53.23

where the first is considered the network as such (when is that used?
I never found out that) and the last one is the broadcast address for
that network. However, the gateway address is not part of that network,
and so the routing algorithm does not know how to reach it.

Even when the gateway is reachable, routing over it does not work (for
me, at least) unless you also add a host route.

sudo route add -host 10.0.0.138 eth0

I have never understood why this is required. I seems to indicate that
the usual mechanism for direct transmission is not used for gateways,
and so I suspect that it is actually possible to use a gateway that is
not on the same network at the configured IP address/mask, thanks
to the host route. You could try it, just execute the host route
command shown above, and see if a subsequent gateway command works.

Indeed, I just tried it on my computer, and it works. (Of course I could
not try sending anything over it, but the route add commands worked; I
could list the routes with netstat -rn.)

-Enrique

In message <slrndr5qsd.9c.ibuprofin.DeleteThis@compton.phx.az.us>
ibuprofin.DeleteThis@painkiller.example.tld (Moe Trin) wrote:

> On Wed, 28 Dec 2005, in the Usenet newsgroup comp.os.linux.setup, in article
> <43b1d7dc$0$3797$9b4e6d93@newsread2.arcor-online.net>, Tamer Higazi wrote:
>
> >I have received from my ISP an IP, DNS, Subnetmask and the DNS
> >Serverentries to add to my ubuntu linux machine

I *think* what you have is the information for connecting your machine via a
modem. You appear however to be using a router.

The interpretation, if my guess is correct is as follows:

On the WAN (ADSL or whatever) side of your router are two addresses -
81.10.53.21, and 81.10.53.22. One of these is your router's IP address for
the WAN interface, and the other is the remote end of the link. You don't
need to worry about these if your router is connecting.

On the LAN side of your router, i.e. the wiring between the router and your
machine, you are using the private network 10.0.0.x. For this to work your
machine needs to have an address in the 10.0.0.<1-254> range. The router is
10.0.0.138, so don't use that for your machine.

(For this network, the "official" subnet mask is 255.0.0.0, giving addresses
from 10.0.0.1 to 10.255.255.254. However you need to use the mask that is
set on the router, which may be different. Addresses below 10.0.0.254 will
work with any likely mask, provided the mask you set on your machine does
match that on the router.)

You may well find that the router is also the DNS server and DHCP server,
which simplifies things quite a lot.

I can't help you with the routing commands - I'm new to Linux myself.

>
> The information is wrong.
>
> >iface eth0 inet static
> >address 81.10.53.22
> >netmask 255.255.255.252
>
> Looking at RFC1878, that mask says there are four IP addresses on this
> segment:
>
> 81.10.53.20 "Network" address - probably not usable for a host
> 81.10.53.21
> 81.10.53.22
> 81.10.53.23 "Broadcast" address - not usable
>
> >gateway 10.0.0.138
>
> And how does one reach that address? It is not one of the four addresses
> noted above.
>
> >My File /etc/hosts:
>
> Generally, it is a good idea to list the IP address of "this" host, so it
> can boot properly if the name server is not reachable.
>
> >If I enter the command route:
>
> Yes
>
> >sudo route add default gateway 10.0.0.138 eth0
> >
> >I receive this errormessage:
> >SIOCADDRT: Das Netzwerk ist nicht erreichbar (Network unreachable)
>
> Yes - because you can not reach 10.0.0.138 from 81.10.53.20/28. The
> gateway MUST be on the "local" interface (which _probably_ means it
> is 81.10.53.21).
>
> Old guy

--
Alan Adams, from Northamptonshire
alan.adams.DeleteThis@orchard-way.freeserve.co.uk
http://www.nckc.org.uk/

On Thu, 29 Dec 2005, in the Usenet newsgroup comp.os.linux.setup, in article
<772213e14d.Alan.Adams.RemoveThis@orchard-way.freeserve.co.uk>, Alan Adams wrote:

>On the LAN side of your router, i.e. the wiring between the router and your
>machine, you are using the private network 10.0.0.x. For this to work your
>machine needs to have an address in the 10.0.0.<1-254> range. The router is
>10.0.0.138, so don't use that for your machine.
>
>(For this network, the "official" subnet mask is 255.0.0.0, giving addresses
>from 10.0.0.1 to 10.255.255.254.

Couple of problems. Who is defining the "official" in the sentence above?
Are you assuming that because the address is between 0.0.0.0 and
127.255.255.255, this must use a 255.0.0.0 or /8? If so, have a look at
RFC1517 to RFC1519 from late 1993 - we're not using Class A, B, or C
address names any more. That would also be a 'network' mask, as putting
16,777,215 hosts on a single subnet is like trying to fit everyone in
London into a single airplane. It would be a very tight fit.

>However you need to use the mask that is set on the router, which may be
>different. Addresses below 10.0.0.254 will work with any likely mask,
>provided the mask you set on your machine does match that on the router.)

Yes, the masks have to match, but "any" likely mask? What about the
255.255.255.252 mask mentioned by the O/P?

>I can't help you with the routing commands - I'm new to Linux myself.

The routing commands actually used are detailed on the 'route' man page.

[compton ~]$ whatis route
route ( - show / manipulate the IP routing table
[compton ~]$

However each distribution has their own cute little tool designed to "help"
with networking setup - only problem is that each tool is very different
from those of other distributions. Also, networking is normally set up at
boot time by scripts and configuration files in /etc/ but as with the tools,
each distribution does it's own thing.

Old guy

In message <slrndrb5bm.rb8.ibuprofin.TakeThisOut@compton.phx.az.us>
ibuprofin.TakeThisOut@painkiller.example.tld (Moe Trin) wrote:

> On Thu, 29 Dec 2005, in the Usenet newsgroup comp.os.linux.setup, in article
> <772213e14d.Alan.Adams.TakeThisOut@orchard-way.freeserve.co.uk>, Alan Adams wrote:
>
> >On the LAN side of your router, i.e. the wiring between the router and your
> >machine, you are using the private network 10.0.0.x. For this to work your
> >machine needs to have an address in the 10.0.0.<1-254> range. The router is
> >10.0.0.138, so don't use that for your machine.
> >
> >(For this network, the "official" subnet mask is 255.0.0.0, giving addresses
> >from 10.0.0.1 to 10.255.255.254.
>
> Couple of problems. Who is defining the "official" in the sentence above?
> Are you assuming that because the address is between 0.0.0.0 and
> 127.255.255.255, this must use a 255.0.0.0 or /8? If so, have a look at
> RFC1517 to RFC1519 from late 1993 - we're not using Class A, B, or C
> address names any more. That would also be a 'network' mask, as putting
> 16,777,215 hosts on a single subnet is like trying to fit everyone in
> London into a single airplane. It would be a very tight fit.
>
> >However you need to use the mask that is set on the router, which may be
> >different. Addresses below 10.0.0.254 will work with any likely mask,
> >provided the mask you set on your machine does match that on the router.)
>
> Yes, the masks have to match, but "any" likely mask? What about the
> 255.255.255.252 mask mentioned by the O/P?

I was assuning, if it wasn't clear, that the 10.0.0.0 network was being
defined by the router. Routers, in my experience usually come set with a
class A or C network defined. (Either 10.0.0.0/8 or 192.168.x.0/24). It is
usual, though obviously not essential, to leave the router set and alter the
rest to match. You can of course alter the router to match your network,
provided you aren't using somebody else's network number, i.e. you need to
be on a private range.

The latter solution is simpler if you already have a network, but it can be
a little tricky to set the router up initially, or after a reset. Using
secondary addresses is the way I solve that one.

>
> >I can't help you with the routing commands - I'm new to Linux myself.
>
> The routing commands actually used are detailed on the 'route' man page.
>
> [compton ~]$ whatis route
> route ( - show / manipulate the IP routing table
> [compton ~]$
>
> However each distribution has their own cute little tool designed to "help"
> with networking setup - only problem is that each tool is very different
> from those of other distributions. Also, networking is normally set up at
> boot time by scripts and configuration files in /etc/ but as with the tools,
> each distribution does it's own thing.
>
> Old guy

--
Alan Adams, from Northamptonshire
alan.adams.TakeThisOut@orchard-way.freeserve.co.uk
http://www.nckc.org.uk/