Two elementary questions on LANs

[Timothy Murphy]

Ed Greshko wrote:

>>I just commented out the IPADDR=192.168.2.7 in this file,
>>as well as NETMASK and GATEWAY, and re-booted,
>>but my IP address remains 192.168.2.7 .
>>In fact the route table has not changed.
>>
>>I ran "sudo grep -r 192.168.2.7  ..." on /etc/ and /var/lib/
>>on the laptop, and there was no match
>>except for the lines I had commented out.
>>
>>There are no wlan0 files in /var/lib/dhclient/ ,
>>so the router does not seem to have sent anything.
>>
>>I looked in /var/log/messages and the first mention of the addressg
>>after the reboot is
>>avahi-daemon[749]: Joining mDNS multicast group
>>  on interface wlan0.IPv4 with address 192.168.2.7.
>>
>>I see from "man avahi-daemon" that avahi-daemon does
>>"register local IP addresses" so that may well be the source of my
>>problems.
>>But if avahi-daemon does save the address I don't see where it does so.
>>It isn't in /etc/ or /var/ .
>>
>>As I said in my original post, if there is any online documentation
>>dealing with this I would very much like to see it.
>>
> 

> Your system is getting its IP address from your dhcp SERVER on you lan, as
> I said.  Your system is a CLIENT.

So you think the Linksys router remembered the old address, 192.168.1.7,
of my laptop, and gave it out despite the fact that its local IP address
is 192.168.2.1 ?

I think if it was giving out an address it would be in the range 100-149,
which is the range it says it offers.

(I'm running the standard Linksys software,
and there doesn't seem to be any way of registering address on it,
as in /etc/dhcpd.conf .)
 
> Now you seem to be mixing things up a bit.  In your original post you
> talked about ifcfg-eth0. Now you talk about wlan0.  Which interface are
> you talking about?

I was actually discussing two different machines.
On my CentOS desktop this LAN is on the interface eth1,
and is connected by ethernet to the router;
on my Fedora laptop it is wlan0, connecting by WiFi.

> What is the bootproto for eth0? And isn't that the interface whose IP
> address you want to change?

I'm not quite sure what you mean.
As I said I have BOOTPROTO=dhcp on my laptop,
which I agree should mean it gets its IP address from the router.
But it doesn't seem to be doing that.

My experience is that if I wait several hours 
and constantly re-boot my laptop,
it will in the end get a new IP address in the 192.168.2.100-149 range.

It seems there is some kind of inertia about changing IP addresses.
It's as though there is a lease somewhere 
and I have to wait for it to expire.

Maybe people don't often try to change the address of a machine,
and so the issue doesn't often arise?

-- 
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