Change and sync hostname / ip address changes on debian linux - linux

Question

For changing static ip address, i set the contents of /etc/network/interfaces to
auto lo
iface lo inet loopback
allow-hotplug eth0
iface eth0 inet static
address <newaddress>
netmask <netmask>
gateway <gateway>
dns-nameservers <dns1> <dns2>
then do ifdown eth0 && ifup eth0
For changing the hostname, i do the following actions
execute hostname <newname>
set contents of /etc/hostname to <newname>
replace <oldname> with <newname> in /etc/hosts
Issues
Both ip address and host name changes don't take effect.
If I change the ip address and ping the hostname, it still resolves to the oldaddress
If I change the hostname and ping the new hostname, it cannot resolve to an ip
If I change the hostname and ping the old hostname, it is still available and resolved the current ip address.
I restart the machine and it still behaves the same way.
What am I missing?
Could the parent network play any role in this?
Also note that my machine thinks the hostname is updated after I change it.

Answer 1

I think this is not actually a problem and this behavior is explained by arp caching.
The ARP tool manipulates or displays the kernel's IPv4 network neighbour and this includes in some way your host as well.
The arp command has many switches you can work on as, for example, the following command:
arp -n
This command prints out the list of arp cache entries.
Unfortunately there is no command to flush it hence, you have 2 options.
Option 1: You wait for the cache to update (won't take long)
Option 2: You run the following very basic script and you see:
#!/bin/sh
for i in `awk -F ' ' '{ if ( $1 ~ /[0-9{1,3}].[0-9{1,3}].[0-9{1,3}].[0-9{1,3}]/ ) print $1 }' /proc/net/arp` ;
do
arp -d $i
done
The script is not mine, I have reported the only I usually run which was taken originally from this well done example:
http://www.lainoox.com/display-add-flush-arpcache-linux-arp/
I hope this helps in some way.

Answer 2

Changing /etc/hostname will have the affect of changing the hostname displayed on your terminal, welcome messages, in your logs and anywhere else the system uses hostname. These are all vanity changes.
Channging /etc/hosts will change your local host-name resolution (i.e. translating an ip address to a hostname and vise versa) Anything DNS does not resolv or anything you want to override locally. By default, the local files override network resolution. This is determined in /etc/nsswitch which says to use local files first then then dns for host resolution.
The important thing to keep in mind here is that these changes will not affect how othesr on a network would determine this host's ip address or name, which of course is handled through DNS or maybe their local /etc/hosts file(s).

Answer 3

yeah resolv.conf is for dns. as is which handles NAMES and anything that has to do with the internet. Such as ping. dns resolvc locally weather you have server or not thus the hostname / ect hosts which ALSO handle dns. your resolv.conf will update from your isp when you connect or you can change it by hand / set some thing more dynamic on a bridged interface