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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
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  • Have you checked which is the Virtual IP which pacemaker manages in case one of the two aliased IP's is the VIP? – Xavy Apr 11 '17 at 13:18
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Imagine an IP address hard coded in a number of configurations, then you need to migrate the service to another machine. Easiest way is to move the IP address to the new server. This might be what happened.

Another idea is that for isolation or management purposes the HA replication might be using one IP, and the web servers might​ be using another.

Using netstat try identifying which servers are connecting to which IP.

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These are aliases.

eth0 = Main interface. eth0.1400 is most probably the vlan interface but if this is not otherwise configured you will run into problems. eth:0.1400 is an alias on eth0

As I'm not using VLANs here you'll have to do some digging:

ip link show
ip a s | grep 1400

should tell you which interface is where and which IP is actually up. Most probably eth0.1400 (without ":") is not working and

ip a s dev eth0

Shows you 10.166.1.9 as an IP bound to eth0.

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