/etc/resolv.conf changes

[Matthew Saltzman]

On Tue, 2008-03-25 at 10:24 -0600, Aaron Konstam wrote:
> On Mon, 2008-03-24 at 17:58 -0400, Matthew Saltzman wrote:
> > On Mon, 2008-03-24 at 16:09 -0600, Aaron Konstam wrote:
> > 
> > > You really can't edit /etc/resolv.conf when you are using a DNS server.
> > > When you are connected to the network it is the DNS nameserver that sets
> > > up the resolv.conf file. In the first case above:
> > 
> > This isn't quite correct.  
> > 
> > /etc/resolv.conf contains the IP addresses of your DNS servers.
> This is a semantic argument. We are talking about wireless. Until you
> connect to the wireless router's AP the resolve.conf computer has no
> idea about the name of your DNS server. The router supplies that form
> the DNS server.

Not semantics at all.  DNS servers don't self-report--and in particular,
they don't reach out and edit clients' /etc/resolv.conf files.  DHCP
servers can provide DNS server information to clients, or not.  If it is
offered, DHCP clients can accept the information (and place it
in /etc/resolv.conf), or not.  For static IP addresses and for DHCP
clients that don't get DNS info from the server, /etc/resolv.conf
contents must be created manually.  

Clients are not required to use the local network's suggestions for DNS
servers--they can use any servers they can reach by IP address.  (For
example, clients can run their own caching nameservers, and just use
127.0.0.1 as the DNS server IP.)

Some wireless routers will get their own IP addresses by DHCP from, say,
a DSL modem (which may in turn get its IP address and DNS server info
from the ISP).  As a DHCP server, the modem may provide DNS server
information to the router.  As a DHCP client, the router may accept that
information or the user may set it (and/or the router's IP address)
manually.

Having the router get DNS from the modem and provide it in turn to
clients is a pretty seamless way to go, and it is quite common
(particularly in home networks), but it is by no means required.

> > 
> > If you connect to your network with a DHCP server, that server provides
> > your IP address and it *may* provide information about DNS servers,
> > which your dhcp client will put in /etc/resolv.conf.  It also may not,
> > or you may decline to use the provided information.  Or you may connect
> > statically.  In that case, you need to hand-edit /etc/resolv.conf or use
> > system-config-network to set static DNS servers.
> > 
> > > > # generated by NetworkManager, do not edit!
> > > > ; Use a local caching nameserver controlled by NetworkManager
> > > > nameserver 127.0.0.1
> > > 
> > > you has not yet made a connection to the internet.
> > 
> > Network manager uses a DHCP client to get your DNS info and places it
> > in /etc/resolv.conf.  If you decline to use that information, you
> > probably have installed a caching nameserver.  In that case, its IP
> > address is 127.0.0.1

-- 
                Matthew Saltzman

Clemson University Math Sciences
mjs AT clemson DOT edu
http://www.math.clemson.edu/~mjs