[CentOS] Centos 6 - Networking: Some Queries

Thu May 17 20:51:05 UTC 2012
Sanjay Arora <sanjay.k.arora at gmail.com>

Hello all

I am setting up a Centos 6 machine with one network card & one onboard
network port. Both are recognized & work. Onboard Network port is unused
yet, but is required for dedicated access to LTSP LAN, which would allow
older PIII machines to boot from this system. I have installed LTSP but
again Networking seems to be the problem area, as the clients won't boot
from this machine.

Have muddled & tinkered with Networking a bit...deleted & reconfigured the
ifcfg files again & again but as I don't understand NetworkManager and
Google is not helping get relevant results, so I have brought the system to
minimum working condition, where one  network card is providing LAN access
on which Internet Router is configured. And now I am posting my system's
condition below as output of various commands.

My network-scripts directory:

[root at swyam network-scripts]# ls
ifcfg-Internet_GW  ifup-eth
ifcfg-lo           ifup-ippp
ifdown             ifup-ipv6
ifdown-bnep        ifup-isdn
ifdown-eth         ifup-plip
ifdown-ippp        ifup-plusb
ifdown-ipv6        ifup-post
ifdown-isdn        ifup-ppp
ifdown-post        ifup-routes
ifdown-ppp         ifup-sit
ifdown-routes      ifup-tunnel
ifdown-sit         ifup-wireless
ifdown-tunnel      init.ipv6-global
ifup               net.hotplug
ifup-aliases       network-functions
ifup-bnep          network-functions-ipv6

Ifconfig output:

[root at swyam network-scripts]# ifconfig
eth0      Link encap:Ethernet  HWaddr E0:69:95:77:A7:F3
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
          Interrupt:20 Memory:fe600000-fe620000

eth1      Link encap:Ethernet  HWaddr 00:60:52:0C:0B:DE
          inet addr:192.168.1.3  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2245698 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1785431 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:3105161344 (2.8 GiB)  TX bytes:148843277 (141.9 MiB)
          Interrupt:16 Base address:0x2000

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:525 errors:0 dropped:0 overruns:0 frame:0
          TX packets:525 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:53459 (52.2 KiB)  TX bytes:53459 (52.2 KiB)

[root at swyam network-scripts]# cat ifcfg-Internet_GW
TYPE=Ethernet
BOOTPROTO=none
IPADDR=192.168.1.3
PREFIX=24
GATEWAY=192.168.1.1
DNS1=218.248.245.1
DNS2=8.8.8.8
DOMAIN="218.248.245.1 8.8.8.8 8.8.4.4"
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="Internet GW"
UUID=d4535709-a05b-459d-a4fd-f08ec9460bcc
ONBOOT=yes
DNS3=8.8.4.4

Network Manager is running and the above card "Internet_GW" was configured
through the NetworkManager applet. Internet works. One can disconnect
Internet through the NetworkManager applet. Yet the applet's Edit
Connection --> Wired --> Last Used status shows "Never".

Now let's come to what I want to do with this machine....The Onboard
network port for LTSP services....Network card on network
192.168.1.0/24(192.168.1.1 is the ISP ADSL router) to provide LAN
access & Internet
access.

Now what I want to do is to create a third network for my virtual machines
(KVM) say 172.16.1.1/24. Now create some sort of dummy bridge and get these
machines talking to the Internet....said bridge to either forward the
packets through the normal Internet path or somehow use NAT to do it. I
think this should be doable but haven't come across any example or any
tutorial for this.

Now comes why I want a separate network....why not use
192.168.1.0/24...problem is...I don't want to disable Network Manager by
putting Managed=NO in my ifcfg file. As with Network Manager enabled, I can
use USB devices whenever my ISP goes down....and I'm afraid it happens more
frequently than I care to bear.

I frankly also don't understand how Network Manager works....in a broad
manner....literature I found was either too technical or too old or was
focussed on a particular problem.

I would like to know a network/bridge/device topology that can solve my
issue....three networks...lan. ltsp, virtual machines, all having access to
each other & the net, while keeping the option of using networkmanager or
any other tool (I'm open) to plugin any other wireless internet access
device.

I am not very advanced admin, but can follow instructions.

Kindly help.

With regards & thanks.
Sanjay.