From: David STAPLETON (davy_stapleton@bikerider.com)
Date: Mon Feb 23 2004 - 04:08:29 EST
Hi folks,
I wonder could somebody clear something up for me regarding setting up IPMP.
I have trawled through the net, the archives, etc. and have found two types of configuration setup for IPMP and it seems to me that if one is correct, the other must be wrong.
The difference in the two methods essentially revolves around the Primary Interface I.P. address and I have found documentation supporting both.
For this query I am not interested in the actual ifconfig syntax, etc. to set up IPMP or some of the caveats, (as in being on the same subnet, etc.). I am only interested in the configuration difference between the two so I'll skip the actual commands.
The two methods are below (All IP address, etc. are fake - well they don't apply to our actual set-up...) :
Assume that pre-setup is the following and already exists ;
Primary interface and I.P. - hme0 : 192.128.254.4 # Designated Primary interface for IPMP
Existing seconday interface - hme1 : 192.128.254.10 # Designated Failover interface for IPMP
Test IP address that you want to use is : 192.128.254.25 (this is obviously a spare address and can be used safely so let's call it the "Spare" I.P. address for clarification)
In method A) You setup the system so that the Primary and Secondary interface I.P. addresses remain the same, by that I mean you add the IPMP group name, etc. and the correct ifconfig options to set it up the IPMP but the I.P. addresses for the Primary and Secondary interfaces are not changed and you add the Spare I.P. address as an alias to the Primary Interface. So you end up with something like the following :
Primary interface and I.P. - hme0 : 192.128.254.4 # Primary interface for IPMP (unchanged)
Existing seconday interface - hme1 : 192.128.254.10 # Failover interface for IPMP (unchanged)
Test Interface (alias) - hme0:1 : 192.128.254.25 # Test interface for IPMP (Spare I.P. address added)
The other method, B) You basically substitute the Test I.P. for the Primary interface address and the Primary Interface address becomes the Test Interface address; The Secondary interface I.P. address remains unchanged, except, as stated above, by adding the IPMP group name and necessary configuration changes to add it to the IPMP configuration. So in the end you have something like the following :
Primary interface and I.P. - hme0 : 192.128.254.25 # Primary interface for IPMP (I.P. changed to Spare I.P. address)
Existing seconday interface - hme1 : 192.128.254.10 # Failover interface for IPMP (unchanged)
Test Interface (alias) - hme0:1 : 192.128.254.4 # Test interface for IPMP (I.P. is the original Primary interface I.P.)
So essentially in method A) all I.P addresses remain unchanged and you just add the Spare I.P. as the Test Alias (hme0:1) and method B) you effectively make the I.P. address for the Primary interface for IPMP the Spare I.P. address and add the former Primary I.P. address as the alias (hme0:1) to the Primary interface.
I hope the explanation is clear and the question is..... Which one is the right way to do it? Intuitively it seems to me that method B is correct as if the Primary fails, the "Test" interface switches to the Failover interface and how could that happen if the Test interface wasn't the original Main I.P. address (i.e. the pingable I.P. address)????
Thanks a million and I will summarise.
David S.
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