Two elementary questions on LANs

Timothy Murphy gayleard at eircom.net
Thu Jun 16 12:10:30 UTC 2011


Ed Greshko wrote:

> On 06/16/2011 07:00 PM, Timothy Murphy wrote:
>> 1) I was trying to change a LAN on my home-system
>> from 192.168.1.0 to 192.168.2.0
>> but I found it surprisingly difficult for example
>> to change my laptop from 192.168.1.7 to 192.168.2.7 .
>> I made the change in /etc/sysconfig/network-scripts/ifcfg-eth1
>> and deleted all the files in /var/lib/dhclient with the old address.
>> But when I re-booted the old address came up,
>> as given by ifconfig and route (or ip route).
>> I was running NetworkManager, but I didn't see
>> the IP address specified in /etc/NetworkManager .
>> I may say the laptop was WiFi connected to a LinkSys router running dhcp,
>> but the Local IP Address in this had been changed to 192.168.2.1 .
>>
>> Who decides the IP address of a device?
> 
> In your /etc/sysconfig/network-scripts/ifcfg-eth1  What is the BOOTPROTO ?
> 
> If it is dhcp then the answer to your question is your dhcp "server".
> 
> The files in /var/lib/dhclient contain the information of you lease that
> is served up by the dhcp server.
> 
> FWIW, that file would also contain dhcp-server-identifier which would
> tell you what system issued the lease.

Thanks for your response.
I have BOOTPROTO=dhcp in /etc/sysconfig/network-scripts/ifcfg-wlan0 .

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 address
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.


-- 
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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