It's actually pretty easy, but there are a few gotchas.

Firstly, I don't think you can get away with doing this without downtime. You 
need to change the IPs of the interface, and the clustering subsystem won't 
react too well to the change of IPs until both are done.

In previous environments, this is how I set it up:

1. Change the IPs of the external interfaces to the private IP range.
2. Using sysconfig, add a new network route for the "real" external subnet and 
when asked for the gateway, leave it empty and hit enter. It should then ask 
you for the outgoing interface name. Type the device name of the external 
interface (e.g. Ext, eth0, etc). This allows the host to see that external 
range (including the all-important default gateway via the correct interface.
3. Add your default gateway or static routes again to point to your external 
router(s).
4. On the cluster topology of your cluster object, edit the relevant external 
interfaces (get the topology to populate the interface names with the private 
IPs), and on the "Cluster IP" interface, set the Cluster IP and subnet mask to 
the real public IP address that you want to use on the Internet. In the "member 
network" tab, enter the network id of the private subnet and the relevant mask 
that you're using for the physical interfaces. The subnet masks for your 
private range and the public range should be the same.

That should instruct ClusterXL to use the physical IPs only for the clustering 
CCP packets, but to consider the public IP as the virtual IP used for outgoing 
/ incoming traffic.

I'm not sure exactly how well this works with proxy arp though. I haven't done 
this recently, but in older versions, I had to use a local.arp file to get the 
cluster to proxy-arp for any NATs that need to exist on the public range (or 
you could just add static routes for them from the Internet router if you 
control the router).

Good luck

Matt


-----Original Message-----
From: Mailing list for discussion of Firewall-1 
[mailto:[email protected]] On Behalf Of Sergio Alvarez
Sent: 09 May 2012 03:55 PM
To: [email protected]
Subject: [FW-1] cluster consuming only one public IP

Hello.

This customer has a cluster made up of two 4000 appliances, as usual, it
was configured consuming 3 public IPs (one for each cluster member and one
as virtual IP for the cluster), now he ran out of public IPs and asks if
something can be done to use a single public IP (virtual one) and use
private IPs on the external interfaces of the cluster members.

I found documentation stating it CAN be done, but it does not provide any
details so I would like to know if anyone here has done it before and can
give me the whole picture.

Besides changing the IPs on each cluster member from public to private, is
there something else that needs to be configured differently? Is there some
sort of downtime when this change is done? Besides the obvious fact that,
from the Internet, it will only be possible to access via SSH or WebGUI the
active cluster member, is there any other implication of doing this change?

Any extra piece of info regarding this scenario anyone can provide, will be
very appreciated.

Regards

-- 
Sergio Alvarez
CISSP | CCSE+

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