dhcpcd - dns only

dhcpcd - dns only

Post by Paulo da Silv » Fri, 10 Dec 2010 11:37:57



Hi!

I have configured my local network using fix local ip addresses and dns
server ips provided by my ISP.

Unfortunately those dns ips do not work as expected most of the times.
Everybody seems to use dhcp.

Is it possible to use dhcpcd (any other linux dhc client?) for dns ips
only keeping local ip addresses fixed?

Thanks.

 
 
 

dhcpcd - dns only

Post by Scott Low » Fri, 10 Dec 2010 12:15:35


On 2010-12-08 21:37:57 -0500, Paulo da Silva said:

Quote:> Hi!

> I have configured my local network using fix local ip addresses and dns
> server ips provided by my ISP.

> Unfortunately those dns ips do not work as expected most of the times.
> Everybody seems to use dhcp.

> Is it possible to use dhcpcd (any other linux dhc client?) for dns ips
> only keeping local ip addresses fixed?

> Thanks.

There are probably a couple of different ways to handle this. At first
glance, you could configure DHCPd with reservations for each of your
systems, so that the systems always get the same IP address. This
allows you the freedom to change the other parameters (such as DNS
servers) without having to reconfigure all the systems, but still
ensures the systems always have the same IP address.

Alternately (and I haven't confirmed this), you might be able to
configure the DHCP client (via dhclient.conf, IIRC) to only obtain
certain pieces of information from the DHCP server. However, I tend to
think that this approach won't work for you. Of course, I could be
wrong (wouldn't be the first time).

Hope this helps!

--
Scott
http://blog.scottlowe.org

 
 
 

dhcpcd - dns only

Post by Paulo da Silv » Fri, 10 Dec 2010 14:37:14


Em 09-12-2010 03:15, Scott Lowe escreveu:

Quote:> On 2010-12-08 21:37:57 -0500, Paulo da Silva said:

>> Hi!

>> I have configured my local network using fix local ip addresses and dns
>> server ips provided by my ISP.

>> Unfortunately those dns ips do not work as expected most of the times.
>> Everybody seems to use dhcp.

>> Is it possible to use dhcpcd (any other linux dhc client?) for dns ips
>> only keeping local ip addresses fixed?

>> Thanks.

> There are probably a couple of different ways to handle this. At first
> glance, you could configure DHCPd with reservations for each of your
> systems, so that the systems always get the same IP address. This allows
> you the freedom to change the other parameters (such as DNS servers)
> without having to reconfigure all the systems, but still ensures the
> systems always have the same IP address.

OK. I used the dhcpcd -r <pretended ip address> and it worked.

I had tried that before but I was requesting an address out of the pool
of addresses reserved for dhcp on my router and it failed.

So I just need to reconfigure the router for a new range of dhcp
addresses and then use -r <ip> for each computer.

Thank you very much.
Paulo

 
 
 

dhcpcd - dns only

Post by Allodoxaphobi » Sat, 11 Dec 2010 00:50:45



> I have configured my local network using fix local ip addresses
> and dns server ips provided by my ISP.

> Unfortunately those dns ips do not work as expected most of
> the times.  Everybody seems to use dhcp.

You are not restricted to using _just_ your ISP's dns servers.
You can set 3 (or more?) _diverse_ dns servers in /etc/resolv.conf
I purposely do _not_ use my ISP's dns servers, and I use one
dns server from each of three diffrent internet 'biggies'.

Example:
|$ cat /etc/resolv.conf
|domain ......
|
|# From `namebench` 14-Sep-10:
|nameserver 128.xxx.xxx.xxx
|nameserver 68.xxx.xx.xxx
|nameserver 205.xxx.xx.x

Recommended: `namebench`  -- download and run to locate the closest,
fastest dns servers/resolvers near you.  

        http://code.google.com/p/namebench/

HTH,
Jonesy
--
  Marvin L Jones    | jonz          | W3DHJ  | linux

    * Killfiling google & XXXXbanter.com: jonz.net/ng.htm

 
 
 

dhcpcd - dns only

Post by Lawrence D'Oliveir » Sat, 11 Dec 2010 06:42:23




> You are not restricted to using _just_ your ISP's dns servers.
> You can set 3 (or more?) _diverse_ dns servers in /etc/resolv.conf
> I purposely do _not_ use my ISP's dns servers, and I use one
> dns server from each of three diffrent internet 'biggies'.

Only my router machine is set to use external DNS servers. The others go via
the router machine, which runs dnsmasq.
 
 
 

dhcpcd - dns only

Post by Moe Tr » Sun, 12 Dec 2010 04:46:39


On 9 Dec 2010, in the Usenet newsgroup comp.os.linux.networking, in article



>> Unfortunately those dns ips do not work as expected most of
>> the times.  Everybody seems to use dhcp.

Please understand that DNS works by believing the first answer it
receives from a name server.   If you list three, two of which are
"real" DNS servers out on the Internet, and the third being something
local like your router,  the kernel resolver code will ask each in
turn.  If you ask about an real Internet hostname such as 'google.com'.
all three servers should return "useful" data, and your system will
believe the first answer it receives.      If you ask a real server
about a local hostname that only your local name server knows about,
the real server will reply

   0/1/0 www.funky.name  NXDOMAIN

which says 'www.funky.name' doesn't exist - and your resolver now
has an answer and the game is over.    ANY NAME SERVER YOU USE MUST
BE ABLE TO RESOLVE ALL NAMES.

Quote:>You are not restricted to using _just_ your ISP's dns servers.

True, but some name server administrators configure their name
servers to either not respond to "outsider" requests for "outside"
names, or have it respond with an NXDOMAIN which may be worse for you.

Quote:>You can set 3 (or more?) _diverse_ dns servers in /etc/resolv.conf

man 5 resolver    and read the section on 'nameserver' directives.
Most kernels are compiled with MAXNS set to '3' in /usr/include/resolv.h,
and additional 'nameserver' lines are ignored.

Quote:>I purposely do _not_ use my ISP's dns servers, and I use one
>dns server from each of three diffrent internet 'biggies'.

I find it more reliable to run my own full recursive name servers.
To prevent abuse from outside, I merely block inbound packets to 53/udp
and 53/tcp.  That way, my internal systems can resolve internal AND
external names from the same server.

        Old guy

 
 
 

1. DHCPcd / DNS Not Agreeing

I just upgraded from Redhat 7.1 to Redhat 7.3.  I also just upgraded from
56k dialup to Cable Modem access through Time Warner Cable and Earthlink.
They refuse to support Redhat (of course), but I dual boot with Windows 2000
and the same problem occurs for Windows 2000.  (On a side note, I guess it
is not really a problem, more like an annoyance.)  I use the -H and -D
options with dhcpcd so dhcpcd attempts to get both the hostname and domain
name for my machine from the dhcp server.  The dhcp server usually returns
something like this dhcp-777-23.earthlink.net.
If you try a ping or a dig or an nslookup on this, you get back unknown
host.  But if you do a dig -x on the ip address returned by the dhcp server
it shows that my ip address is mapped to the name:
user1-5cdsjho.cable.mindspring.com
So, it seems to me that the DHCP server and the DNS server are not agreeing
over what name to assign my machine.  This gets me error messages when I do
things like "hostname -f", and cups print server gives me stuff like
Get_local_host: hostname 'yourmadeupname.earthlink.net' bad.
I've tweaked the dhcpcd configuration files, resolv.conf, host.conf, and a
multitude of other items with no luck.  Keeping in mind of course that I can
access the internet with tremendous broadband speed, could someone post a
hypothesis?
Thanks!

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