proper ip address aliasing
Rick Stevens
rstevens at vitalstream.com
Thu Feb 3 00:20:40 UTC 2005
Ken Scott wrote:
> On Wed, 2005-02-02 at 12:59, Rick Stevens wrote:
>
>>jdyke wrote:
>>
>>>I need to add a group of virutal ips to a single interface on FC3. I've
>>>used
>>>`ip addr add 192.168.2.XX dev eth0` to add the ips which worked fine,
>>>but what is the best/proper way to add them at boot up. I'd assume i
>>>could add them in rc.local which should work? but is that right?
>>
>>The proper way is to create additional scripts in the
>>"/etc/sysconfig/network-scripts" directory. They should be named
>>"ifcfg-eth0:x", with "x" being the alias number. If you're adding 3
>>aliases to eth0, for example, the files would be:
>>
>> ifcfg-eth0 (primary, leave it alone)
>> ifcfg-eth0:1 (first alias)
>> ifcfg-eth0:2 (second alias)
>> ifcfg-eth0:3 (third alias)
>>
>>Inside those "ifcfg-eth0:x" scripts, you only need four lines:
>>
>> DEVICE=eth0:x (replace "x" with the alias number)
>> IPADDR=xxx.xxx.xxx.xxx
>> NETMASK=xxx.xxx.xxx.xxx
>> ONBOOT=yes
>>
>>The first one, "ifcfg-eth0" should be left alone, as it sets up the
>>base device.
>>
>>That's the "official" way to do it and the way "system-config-network"
>>or "Fedora Icon->System Settings->Network" do it, which would allow you
>>to manage them via the GUI system.
>
>
> I have not had occasion to use this "virtual IP" technique but I
> appreciate the procedure.
Technically it's called "IP aliasing".
> Does this mean that I can take my development
> box (192.168.0.100) and assign it a virtual IP on a different subnet
> (say 192.168.2.100) so that it could talk to a another box I have on
> the local network temporarily (which I am working on for someone else)?
> My machine only has a single network card in it.
Yes you can, but you have to be careful as your switch/router may not
allow you to cross subnet boundries. For most people it'll work fine.
> That would be great if true, I could leave both my machine's IP alone
> and the other device's IP as well and simply change the virtual IP so
> that they could talk.
We do it a lot, but again, watch your routers and switches. Also
remember that your _default_ route will remain the same. It will add
another _network_ route, but not a default one.
> Seems so elegant that it probably does work that way (since it is after
> all Linux)!
Simple is elegant. That's Unix/Linux in a nutshell.
> I know that I can change my internal IP to match the target machine but
> that solution doesn't allow concurrent web access.
This is the cheap solution.
Historical note: Before hostheaders were invented in HTTP 1.1, this is
how you got a web server to handle multiple websites. Each site got an
individual IP address and you aliased the NIC card out the wazoo.
----------------------------------------------------------------------
- Rick Stevens, Senior Systems Engineer rstevens at vitalstream.com -
- VitalStream, Inc. http://www.vitalstream.com -
- -
- Careful! Ugly strikes 9 out of 10 people! -
----------------------------------------------------------------------
More information about the Redhat-install-list
mailing list