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I have an dedicated unmanaged server and added a few IP addresses to it (allocated), and the only information my hosting company has provided is instructions on how to use Plesk to Add IP Addresses. However, one of the first things I did was uninstall Plesk (for numerous reasons).

Does anyone know what exactly Plesk does when you "Add IP Address"? Does it just create an alias on the default interface (I currently only have one and the loopback)? I can manage that myself without Plesk, but I was hoping someone might know if there is anything else Plesk does. I also have DHCP Client running (eth0 is static), not sure why my hosting company put that there either, and not sure if they're related.

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2 Answers 2

If your hosting company is using a DSR ( Direct Server Return ) load balancing environnement, you have to add the ip address as an alias of the loopback interface, and you also have to check in /etc/sysctl.conf that the following settings are activated:

net.ipv4.conf.all.arp_ignore = 1 net.ipv4.conf.all.arp_announce = 2

Beside this, the obvious point is to check your apache configuration: if your <virtualhosts> directives are bound to specific IP addresses, or if your Listen directives are bound to specific ip address you have to update them.

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Ok. Maybe safest is to first add it to loopback (ip addr add 1.2.3.4/32 dev lo) and see if it works from outside. If not you have to remove it and add it to eth0. After this you can either put the command to /etc/rc.local or to the correct place according to distro. RHEL/Centos /etc/sysconfig/network-scripts/ifcfg-eth0 Debian/Ubuntu /etc/network/interfaces –  anttiR Nov 9 '11 at 7:12
up vote 0 down vote accepted

Hosting company finally responded:

Changed default interface to static (from DHCP).

New interfaces (aliases) were created by creating new ifcfg scripts like eth0:n and declaring DEVICE, IPADDR, NETMASK and GATEWAY, with the GATEWAY being the same as the gateway for the default nic.

Then a default routing was created as /etc/sysconfig/network-scripts/route-eth0: dev eth0 default via dev eth0

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