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Logical IP Addresses In SLES9

Novell Cool Solutions: Trench
By Randolph Moeller

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Posted: 4 Mar 2005

I discovered that virtual aliases are not the same as Logical IP addresses, with regards to the fact that you can't remove a Virtual Alias on the fly. And in our environment that is essential. I discovered that creating a logical IP address on an interface that starts with 0 (ie eth1:0) and then creating multiple logical IP addresses below that... (ie eth1:1, eth1:2, eth1:3, eth1:4....) if you remove eth1:0, you will remove them all (which is very bad), however, if you remove eth1:1 or any of the others Logical IP addresses, it will only remove that specific ip address (which is desired). I was able to save my logical IP address information by creating a custom startup script and calling the following commands:

ifconfig eth0:2
route add -host dev eth0:2

People should know that if you attempt to create a logical IP address that starts with zero it will wipe away all the logical IP addresses below that if you remove it on the fly with the ifconfig eth0:0 down command. (This is unlike solaris, where you can do that.)

It is also VERY important that you execute the following command: route add -host <service name | logical IP address> dev <interface> (ex. route add -host dev eth0:1) If you dont do that, it will erase if any of the other IP addresses are erased.

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