I came across this network config on an Ubuntu server and wondered about the reasoning behind the doubled VLAN config. True to form, there's no documentation and the engineers who have worked on the box couldn't enlighten me, so any thoughts!?
The server is in a remote data centre so I can't check out the network topology easily right now. From what I have been able to find out, the box is a database server running MySQL and the VLAN(s!?) link it to the Web server to make up a LAMP stack system. The base eth0 address (public facing, firewalled) is just used for admin ssh logins.
There is supposedly a second (HA) database server using pacemaker and corosync, but the failover is not working right now, hence I am looking at the system to produce some documentation while a more skilled engineer deals with the HA config.
Edit: There's only one VLAN config entry on eth0 on the Web server (10.166.1.7)
# Loopback interface auto lo iface lo inet loopback # Primary network interface auto eth0 iface eth0 inet static address [SNIP] netmask 255.255.255.248 gateway [SNIP] dns-nameservers [SNIP] auto eth0.1400 iface eth0.1400 inet static address 10.166.1.5 netmask 255.255.255.0 vlan-raw-device eth0 auto eth0:1.1400 iface eth0:1.1400 inet static address 10.166.1.9 netmask 255.255.255.0 vlan-raw-device eth0