Protect Your Cloud Infrastructure Servers with Isolated Cloud Networks

Create a Private Cloud Network

Create an isolated cloud network. Here I am using the supernova client to communicate with the Rackspace OpenStack API.

supernova uk network-create "Infrastructure" "192.168.3.0/24"
+----------+--------------------------------------+
| Property | Value                                |
+----------+--------------------------------------+
| cidr     | 192.168.3.0/24                       |
| id       | 4d15b8ad-45c5-4169-a4fa-d36f1a776efd |
| label    | Infrastructure                       |
+----------+--------------------------------------+

Take note of the id – you’ll need it shortly!

Create a Proxy Server and Attach to the Private Network

supernova uk boot proxy-bast --flavor 2 --image 189678ca-fe2c-4b7a-a986-30c3660edfa5 --nic net-id=4d15b8ad-45c5-4169-a4fa-d36f1a776efd

The above creates a server using the CentOS 6.6 image. Other images of interest are:

+--------------------------------------+------------------------------------------+--------+
| ID                                   | Name                                     | Status |
+--------------------------------------+------------------------------------------+--------+
| 189678ca-fe2c-4b7a-a986-30c3660edfa5 | CentOS 6 (PVHVM)                         | ACTIVE |
| f8ae535e-67c0-41a5-bf55-b06d0ee40cc2 | CentOS 7 (PVHVM)                         | ACTIVE |
| 6909f56c-bd77-411a-8c0e-c37876b68d1d | Ubuntu 14.04 LTS (Trusty Tahr) (PVHVM)   | ACTIVE |
+--------------------------------------+------------------------------------------+--------+

Proxy Bastion Configuration

Later we create a cloud server with no public IP, which is protected by sitting behind our proxy bastion. From the bastion side, in order for our protected server to have access to the internet, we need to apply firewall rules for IP forwarding and Network Address Translation. This process differs depending on which distribution you use. Here I cover CentOS 6.6, CentOS 7 and Ubutnu 14.04.

CentOS 6.6

Under CentOS 6.6 and before, you need to configure IPTables to do the forwarding and the Network Address Translation (NAT). We will be forwarding the traffic from the eth2 interface, out through the eth0 interface. We also use Static NAT or MASQUERADE so that traffic coming from our protected infrastructure, takes on the public IP address of our proxy bastion.

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether bc:76:4e:08:40:d8 brd ff:ff:ff:ff:ff:ff
    inet 95.138.163.75/24 brd 95.138.163.255 scope global eth0
    inet6 2a00:1a48:7805:113:be76:4eff:fe08:40d8/64 scope global 
       valid_lft forever preferred_lft forever
    inet6 fe80::be76:4eff:fe08:40d8/64 scope link 
       valid_lft forever preferred_lft forever
4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether bc:76:4e:08:3d:31 brd ff:ff:ff:ff:ff:ff
    inet 192.168.3.1/24 brd 192.168.3.255 scope global eth2
    inet6 fe80::be76:4eff:fe08:3d31/64 scope link 
       valid_lft forever preferred_lft forever
Enable IP Forwarding

To enable forwarding, you need to enable it in two places. One in /proc/sys/net/ipv4/ip_forward.

echo 1 > /proc/sys/net/ipv4/ip_forward

And the other in /etc/sysctl.conf. The below uses grep check the value of net.ipv4.ip_forward.

grep net.ipv4.ip_forward /etc/sysctl.conf 
net.ipv4.ip_forward = 0

If zero, enable with a one as shown below.

net.ipv4.ip_forward = 1
Configure Static NAT and Forwarding Rules
iptables --table nat --append POSTROUTING --out-interface eth0 -j SNAT --to 95.138.163.75
iptables --append FORWARD --in-interface eth2 -j ACCEPT
service iptables save

We also need to remove the default reject rule on the FORWARD’ing table:

iptables -D FORWARD 1

Here I delete rule number one from the FORWARD table. Make sure you delete the correct line. To see the line numbers, use:

[root@proxy-bast ~]# iptables -vnL --line-number
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1    44444   62M ACCEPT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           ctstate RELATED,ESTABLISHED 
2        0     0 ACCEPT     icmp --  *      *       0.0.0.0/0            0.0.0.0/0           
3        0     0 ACCEPT     all  --  lo     *       0.0.0.0/0            0.0.0.0/0           
4        1    60 ACCEPT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0           ctstate NEW tcp dpt:22 
5        1    40 REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           reject-with icmp-host-prohibited 

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1        0     0 REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0           reject-with icmp-host-prohibited 

Chain OUTPUT (policy ACCEPT 8769 packets, 544K bytes)
num   pkts bytes target     prot opt in     out     source               destination

Make sure you have restarted everything.

service iptables restart
service network restart

Now configure the default gateway on the infrastructure server.

CentOS 7

With the introduction of firewalld, CentOS 7 now does things a little differently.

Method 1

This method uses the predefined zones available to us and is by far the easiest method to apply. The external zone has IP masquerading enabled by default so there should be little to do.

Define Your Zones

To view your zone setup.

[root@proxy-bast ~]# firewall-cmd --get-default-zone
public
[root@proxy-bast ~]# firewall-cmd --get-active-zones
public
  interfaces: eth0 eth1 eth2

To see the supported predefined zones , use the --get-zones–list-all-zones option.

firewall-cmd --list-all-zones

The zones I will be using are external, work and internal.

external
  interfaces: 
  sources: 
  services: ssh
  ports: 
  masquerade: yes
  forward-ports: 
  icmp-blocks: 
  rich rules:

work
  interfaces: 
  sources: 
  services: dhcpv6-client ipp-client ssh
  ports: 
  masquerade: no
  forward-ports: 
  icmp-blocks: 
  rich rules: 

internal
  interfaces: 
  sources: 
  services: dhcpv6-client ipp-client mdns samba-client ssh
  ports: 
  masquerade: no
  forward-ports: 
  icmp-blocks: 
  rich rules: 

My setup looks like this…

Port	Firewall Zone	Name						IPv4				
------------------------------------------------------------------------
eth0	external		PublicNet (Internet)		162.13.87.197		
eth1	work			ServiceNet (Rackspace)		10.179.198.73		
eth2	internal		Infrastructure				192.168.3.1

…and can be achieved with the below commands. Don’t forget to restart firewalld!

firewall-cmd --permanent --zone=external --change-interface=eth0
firewall-cmd --permanent --zone=work --change-interface=eth1
firewall-cmd --permanent --zone=internal --change-interface=eth2
firewall-cmd --reload
systemctl restart firewalld
Method 2

With this method we use the --direct option so we can include traditional iptable rules.

Enable IP Forwarding

This step is not needed if you are using the predefined “external” zone provided by firewalld, as masquerade is enabled by default already.

echo "net.ipv4.ip_forward=1" >> /etc/sysctl.conf

To check its enabled.

[root@proxy-bast ~]# sysctl -p
net.ipv4.conf.eth0.arp_notify = 1
vm.swappiness = 0
net.ipv4.ip_forward = 1
Configure Static NAT and Forwarding Rules
firewall-cmd --permanent --direct --passthrough ipv4 -t nat -I POSTROUTING --out-interface eth0 -j SNAT --to 162.13.87.197
firewall-cmd --permanent --direct --passthrough ipv4 --append FORWARD --in-interface eth2 -j ACCEPT
firewall-cmd --reload

systemctl restart network
systemctl restart firewalld
Method 2

Revert back to the tried and tested iptables.

Revert back to Using IPTables
systemctl stop firewalld
systemctl disable firewalld

iptables-service

touch /etc/sysconfig/iptables
systemctl start iptables
systemctl enable iptables

touch /etc/sysconfig/ip6tables
systemctl start ip6tables
systemctl enable ip6table

Now you can follow the instructions for CentOS 6.6.

Ubuntu 14.04 LTS

In Ubuntu we use the Uncomplicated Firewall (UFW).

Enable IP Forwarding

Use a text editor to open up the below file as root…

nano /etc/default/ufw

…and enable the default forward policy – change to ACCEPT.

DEFAULT_FORWARD_POLICY="ACCEPT"

We also need to edit the below…

nano /etc/ufw/sysctl.conf

…and uncomment the following lines.

net/ipv4/ip_forward=1
net/ipv6/conf/default/forwarding=1
Configure Static NAT and Forwarding Rules

As root, open the below file.

nano /etc/ufw/before.rules

From the top, my configuration file looks like the below. I inserted the lines in bold.

#
# rules.before
#
# Rules that should be run before the ufw command line added rules. Custom
# rules should be added to one of these chains:
#   ufw-before-input
#   ufw-before-output
#   ufw-before-forward
#
# nat Table rules
*nat
:POSTROUTING ACCEPT [0:0]
:PREROUTING ACCEPT [0:0]

-A POSTROUTING -s 192.168.3.0/24 -o eth0 -j SNAT --to-source 162.13.87.197
-A PREROUTING -i eth2 -j ACCEPT
COMMIT


# Don't delete these required lines, otherwise there will be errors
*filter
:ufw-before-input - [0:0]
:ufw-before-output - [0:0]
:ufw-before-forward - [0:0]
:ufw-not-local - [0:0]
# End required lines


# allow all on loopback
-A ufw-before-input -i lo -j ACCEPT

...

You will need to restart ufw for the changes to take effect.

ufw disable && sudo ufw enable

For some reason this wiped my SSH rule:

ufw allow ssh
ufw reload
ufw status verbose

Create Infrastructure Server

Here we spin-up a server connected to our isolated cloud network and no public interface. All communications must go via the proxy-bast server.

supernova uk boot protected --flavor 2 --image 189678ca-fe2c-4b7a-a986-30c3660edfa5 --nic net-id=4d15b8ad-45c5-4169-a4fa-d36f1a776efd --no-service-net --no-public

Configure Internet Gateway

Here we simply need to route the traffic through the proxy bastion. We do this by defining it as our default gateway. We also need to set our DNS servers.

CentOS 6.6

Simplicity!

echo "GATEWAY=192.168.3.1" >> /etc/sysconfig/network
echo "nameserver 83.138.151.80" >> /etc/resolv.conf
echo "nameserver 83.138.151.81" >> /etc/resolv.conf
service network restart

CentOS 7

The default image provided by Rackspace comes with nmcli disabled. As such the process is similar to previous releases.

echo "GATEWAY=192.168.3.1" >> /etc/sysconfig/network
echo "nameserver 83.138.151.80" >> /etc/resolv.conf
echo "nameserver 83.138.151.81" >> /etc/resolv.conf
echo "DNS1=83.138.151.80" >> /etc/sysconfig/network-scripts/ifcfg-eth0
echo "DNS2=83.138.151.81" >> /etc/sysconfig/network-scripts/ifcfg-eth0
systemctl restart network

Ubuntu 14.04 LTS

To define the default gateway, you need to edit the /etc/network/interfaces file.

nano /etc/network/interfaces

Mine looks like this. Make sure to add the gateway.

auto eth0
iface eth0 inet static
    address 192.168.3.4
    netmask 255.255.255.0
    gateway 192.168.3.1

You will need to manually add Rackspaces name servers to your resolv.conf. However on Ubuntu this file is automatically generated. Instead we editing /etc/resolvconf/resolv.conf.d/base and regenerate the file using the resolvconf command.

root@protected:~# cat /etc/resolv.conf 
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
root@protected:~# echo "nameserver 83.138.151.80" >> /etc/resolvconf/resolv.conf.d/base
root@protected:~# echo "nameserver 83.138.151.81" >> /etc/resolvconf/resolv.conf.d/base
root@protected:~# resolvconf -u
root@protected:~# cat /etc/resolv.conf 
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 83.138.151.80
nameserver 83.138.151.81

I needed to reboot for the changes to take effect.

reboot

Related Documents

Rackspace Developer Blog: Protect your Infrastructure Servers with Bastion Hosts and Isolated Cloud Networks

Rackspace Developer Blog: Supernova: Managing OpenStack Environments Made Easy

Rackspace Knowledge Centre: Using OnMetal Cloud Servers through API

Fedora: Firewalld

Oracle-Base: Linux Firewall (firewalld, firewall-cmd, firewall-config)

Kevin’s Cheat Sheet: Configure iptables to act as a NAT gateway

Rackspace Developer Blog: Getting Started: Using rackspace-novaclient to manage Cloud Servers

James Rossiter: Forward ports in Ubuntu Server 12.04 using ufw

Ubuntu Documentation: Firewall

Github: UFW

Code Ghar: Ubuntu 12.04 IPv4 NAT Gateway and DHCP Server

Linux Gateway: A More Complex Firewall

netfilter.org: Saying How to Mangle the Packets

Ubuntu Documentation: IptablesHowTo

Major.io: Delete single iptables rules

iptables.info: Iptables

snipt.net: Insert an iptables rule on a specific line number with a comment, and restore all rules after reboot

stackexchange.com: How do I set my DNS on Ubuntu 14.04?

thesimplesynthesis.com: How to Set a Static IP and DNS in Ubuntu 14.04

Rackspace Knowledge Centre: Ubuntu – Setup

Rackspace Knowledge Centre: Introduction to iptables

Rackspace Knowledge Centre: Sample iptables ruleset

Ubuntu Geek: Howto add permanent static routes in Ubuntu

NixCraft: Debian / Ubuntu Linux Setting a Default Gateway

Ask Ubuntu: Set up permanent routing (Ubuntu 13.04)

cviorel.com: How to set up a VPN server on Ubuntu

Redhat Support: 10.4. Static Routes and the Default Gateway