On Tue, 2 Jun 1998 [EMAIL PROTECTED] wrote:
> We are in the process of changing Networks. And I need a way to switch
> our web machines from one network to the other with no downtime. At first
> we were going to mirror the machines on both networks. But, i think there
That would work. In the case of a physical disparity between the networks
(i.e. they are different wires) that is the only way to do it with zero
downtime, since you would have to shut off your computer to change the
ethernet card.
If you are only changing network numbers, not physical networks, you can
do this easily.
If you are not changing technologies, but only wires (i.e. you are going
to unplug one ethernet wire from your card and plug a different one in but
you don't need a new network card) then you can combine the following two
strategies to get, if not exactly zero downtime, a downtime of only a few
seconds.
> is a better way. Could I add a second ethernet card to the machines and
> set it up for the new network? That way he same machine is on both
That's going to imply some downtime, isn't it. :)
If you are simply renumbering your existing Ethernet, you can simply add
another IP address (and netmask, etc.) to your existing Ethernet card so
it talks on both networks at once. Then when you shut off the other
network, you simply remove the old IP address.
In this case you will need to make use of IP-aliasing. I don't know if
this capability can be loaded as a module (I don't think it can) or, if
not, whether Red Hat's default kernel comes with it. If it doesn't, or if
you compiled your own but without the IP-aliasing option, you will not be
able to do it this way. You would have to at the very least recompile
your kernel and reboot.
If you have IP aliasing, you can use something like
ifconfig eth0:0 10.23.54.2 netmask 255.255.255.0
That would add the 10.23.54.2 IP address to the eth0 card, with the given
netmask, it should be able to guess the rest of the data it needs
automatically.
If you mean you are physically changing networks (10baseT to 100baseT, for
example) then you could do as you suggested before and install a new
network card, using them both at once. But you need to use kernel
commandline options, or manually load your network card drivers as
modules, so it can see both ethernet cards at once. And of course you
have to shut down to put in the new card.
If you are changing networks but not technologies, then you can add the
network alias to your network card ahead of time. Now your network card
has a valid address for the network it is on, and a valid address for the
network it is going to be on. But the numbers for one network are not
valid for the other one. After you have this set up, simply swap your
network cable out. You don't have to even reboot or shut off the
computer. Now all of a sudden the valid IP becomes invalid and the
invalid one becomes valid. But if no one tells your computer, it won't
even notice. :) You can then safely remove the old, now invalid, IP
address.
> networks. Also, would Apache have probalems with this?
No. You don't even have to restart httpd.
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