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How to Configure an Additional IP Block on a vRack

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Michael M.
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Objective

As well as private IP addressing, the vRack also allows you to route public IP traffic through your server’s vRack port using a public IP address block.

This guide will show you how to configure a block of public IP addresses for use with the vRack.

Note: VLAN tagging is not supported when configuring an additional IP block on vRack so make sure any traffic you send over the vRack is untagged. Additionally, traffic over any given vRack cannot exceed 600 Mbps.

Requirements

  • a public block of IP addresses in your account, with a minimum of four addresses
  • your chosen private IP address range
  • a vRack compatible server
  • a vRack service activated in your account
  • access to the OVHcloud Manager

Instructions

For example purposes, we’ll be using an IP block of 46.105.135.96/28 and eth1 for the secondary network interface, which is dedicated to the vRack.

Configure a usable IP address

For vRack purposes, the first, penultimate, and last addresses in any given IP block are always reserved for the network address, network gateway, and network broadcast respectively. This means that the first useable address is the second address in the block, as shown below:

46.105.135.96   Reserved: Network address
46.105.135.97   First usable IP
46.105.135.98
46.105.135.99
46.105.135.100
46.105.135.101
46.105.135.102
46.105.135.103
46.105.135.104
46.105.135.105
46.105.135.106
46.105.135.107
46.105.135.108
46.105.135.109  Last usable IP
46.105.135.110  Reserved: Network gateway
46.105.135.111  Reserved: Network broadcast

To configure the first usable IP address, we need to edit the network configuration file, as shown below. In this example, we need to use a subnet mask of 255.255.255.240.

Note: The subnet mask we’ve used in our example is appropriate for our IP block. Your subnet mask may differ depending on the size of your block. When you purchase your IP block, you’ll receive an email that will tell you which subnet mask to use.

/etc/network/interfaces

auto eth1
iface eth1 inet static
address 46.105.135.97
netmask 255.255.255.240
broadcast 46.105.135.111

Create a new IP routing table

First, we need to download and install iproute2, which is a package that will enable us to manually configure IP routing on the server.

Establish an SSH connection to your server and run the following command from the command line. This will download and install iproute2.

# apt install iproute2

Next, we need to create a new IP route for the vRack. We will be adding a new traffic rule by amending the file, as shown below:

/etc/iproute2/rt_tables

#
# reserved values
#
255 local
254 main
253 default
0   unspec
#
# local
#
#1  inr.ruhep
1 vrack

Amend the network configuration file

For example purposes, the network configuration file we refer to is located in /etc/network/interfaces. The equivalent file on your server may be located somewhere else, depending on your operating system.

Finally, we need to amend the network configuration file to account for the new traffic rule and route the vRack traffic through the network gateway address of 46.105.135.110.

/etc/network/interfaces

auto eth1
iface eth1 inet static
address 46.105.135.97
netmask 255.255.255.240
broadcast 46.105.135.111
post-up ip route add 46.105.135.96/28 dev eth1 table vrack
post-up ip route add default via 46.105.135.110 dev eth1 table vrack
post-up ip rule add from 46.105.135.96/28 table vrack
post-up ip rule add to 46.105.135.96/28 table vrack

Now reboot your server to apply the changes.

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