Building a DMZ lab for pentesting in GNS3 and VMWare Workstation9 (Part II: Basic Layout)

Hello again, fellows.

Today we’re using the preconfigured (see Part I) GNS3 to build our basic lab. Imagine the following scenario:

Your pentesting company got contracted by a small company to do a white/grey box pentest. This means you know everything about the present IT infrastructure and got all info on software patchlevels and hardware used. And to safely mitigate possible downtimes or other unforseen consequences of a full-blown pentest on the production network, network simulation comes in handy.

Also if your pentesting company is contracted to do a black box pentest a virtual network that is built on findings from the information gathering process can be used as a test environment before actually conducting the test on the real systems.

As for our pentest we choose a mid-sized software company called Noob.net with the following network properties:

  • Dual firewall DMZ with port forwarding
  • Webserver & Services (Email, DNS, etc.) in DMZ
  • Internal network that is split into VLANs according to department (Management, IT, Software Development, Sales)
  • Routing via OSPF, backed up by static routes

As prerequisites you need at least two different iOS images and one PIX image. In our case we use the following:

Firewall: PIX 803

Router_FW_Internal: c3725-advsecurityk9-mz.124-19b.image

RouterDMZ & Router_ISP: c2691-jk9s-mz.123-17.image

Pic4_Pix_config

PIX configuration in GNS3

Additionaly you should have a few virtual machine handy that to do ping/traceroute tests. I use a Windows XP SP3 and a Kali Linux VM to do so.

First of before we start we need to assign IP and subnet addresses and VLANs. The following table includes all the information necessary to model your virtual networks after.

Note: Due to the constraints of the VMWare Networks I only used subnetting on the interfaces that interconnect the routers with the firewall (PIX).

Dept. VLAN If. # of IP-Add. CIDR Network Subnet Mask
Management 10 F0/1 @ Router 254 /24 10.10.10.0 255.255.255.0
IT (DMZ) 254 /24 172.16.100.0 255.255.255.0
Software Development 200 F1/0 254 /24 10.10.200.0 255.255.255.0
Sales 300 F2/0.30 @ Router 254 /24 10.10.30.0 255.255.255.0
Marketing 400 F2/0.40 @ Router 254 /24 10.10.40.0 255.255.255.0
Internet” 254 /24 192.168.10.0 255.255.255.0
Internal ↔ PIX F0/0 @ router e0 @ PIX 2 /30 10.0.0.0 255.255.255.252
PIX ↔ DMZ E1 @ PIX F0/0 @ DMZ 2 /30 192.168.0.0 255.255.255.252
PIX ↔ Ext E4 @ PIX F0/0 @ Ext 2 /30 192.168.0.4 255.255.255.252

The next table shows the interal (Router_FW_Internal) router’s ports and their connectivity:

If Connected to IP-Address VLAN
F0/0 Firewall External @ E0 10.0.0.1
F0/1 Management_Switch @ 1 10.10.10.2 10
F1/0 SoftwareDev_Switch @ 1 10.10.200.2 200
F2/0 Setup_Interface 10.10.20.1 dot1q
F2/0.300 Sales_Marketing_Switch @ 1 10.10.30.2 30
F2/0.400 Sales_Marketing_Switch @ 1 10.10.40.2 40

The following table shows the Firewall’s (PIX) connections.

Port Connected to IP Address / CIDR
E0 Router_FW_Internal @ F0/0 10.0.0.2 /30
E1 Router_DMZ @ 1 192.168.0.1 /30
E5 Router_ISP @ 1 192.168.0.5 /30

The following table shows the Router_ISP’s connections

Port Connected to IP Address / CIDR
F0/0 PIX @ E4 192.168.0.6 /30
F0/1 Internet @ vmware8 192.168.10.2 /24

The following table shows the RouterDMZ’s connections

Port Connected to IP Address / CIDR
F0/0 PIX @ E1 192.168.0.2 /30
F0/1 Internet @ vmware13 172.16.100.2 /24

The next table shows the Virtual Networks used and their configuration:

Name IP Range resembles VLAN
Vmnet8 192.168.10.0/24 Internet
Vmnet13 172.16.100.0/24 IT (DMZ)
Vmnet14 10.10.10.0/24 Management 10
Vmnet16 10.10.200.0/24 SoftwareDev 200
Vmnet17 10.10.300.0/24 Sales 30
Vmnet18 10.10.400.0/24 Marketing 40

Here is a picture what the topology should look like:

Pic5_Topology

Network topology in GNS3

Next we need to configure the router to enable routing between the internal networks and the DMZ and the Internet respectively.

Note that the commands described within this tutorial are always executed from enable mode.

Router_FW_Internal

So we log into the console of Router_FW_Internal and start with the interface facing the internal network that connects to the management LAN. First off, we’re going to apply the correct IP addresses to the corresponding interfaces:

Conf t

int fastEthernet1/1

description toMGMT

no shut

ip address 10.10.10.2 255.255.255.0

full-duplex

exit

Next up we’re going to setup basic security configurations on the switch, starting with the enable secret and password encryption.

conf t

enable secret Cisco1

service password-encryption

Then we’re going to implement SSH connectivity on the standard VTY lines (0-5) and disallow Telnet. But first we have to give the router a qualified domain name and generate a RSA key pair.

ip domain-name noob.net

crypto key generate rsa

→ Choose 1024 to support SSH v.2

line vty 0 5

login local

transport input ssh

ip ssh version 2

motd-banner

exit

line con 0

login local

motd-banner

exit

Then we generate a username with password.

username admin password administrator

Let’s create a banner to warn potential intruders. We also need to enable the messasge-of-the-day banner on the VTY lines.

banner motd # Trespassers will be prosecuted. #

line vty 0 5

motd-banner

exit

Next we will configure interface f1/0. The connection to the Software Development switch:

conf t

int fastEthernet1/0

description toSoftDev

no shut

ip address 10.10.200.2 255.255.255.0

full-duplex

exit

We will configure interface f2/0 as a Router-on-a-stick configuration since Marketing and Sales share the same switch, but they should be on different broadcast domains. Therefore we add the following commands:

conf t

int fastEthernet2/0

description setup_if

ip address 10.10.20.2 255.255.255.0

no shut

exit

int fastEthernet2/0.30

no shut

description to_Sales

encapsulation dot1Q 30

ip address 10.10.30.2 255.255.255.0

no shut

exit

int fastEthernet2/0.40

description to_Marketing

encapsulations dot1Q 40

ip address 10.10.40.2 255.255.255.0

no shut

exit

The next step will connect the internal router/firewall to the external firewall.

conf t

int fastEthernet0/0

no shut

ip address 10.0.0.1 255.255.255.252

description toFirewallExt

We also need to configure static routing as a back-up system. Therefore we will add an administrative distance of 250 to the route:

ip route 0.0.0.0 0.0.0.0 10.0.0.2 250

To prevent access from any unauthorized users we now put a few extended ACLs in place. We start with the access list for int fa0/1 (MGMT). This list will prevent traffic coming from the MGMT network to reach the other local networks.

conf t

access-list 100 remark fromMGMT

access-list 100 deny ip 10.10.10.0 0.0.0.255 10.10.200.0 0.0.0.255 log-input

access-list 100 deny ip 10.10.10.0 0.0.0.255 10.10.20.0 0.0.0.255 log-input

access-list 100 deny ip 10.10.10.0 0.0.0.255 10.10.30.0 0.0.0.255 log-input

access-list 100 deny ip 10.10.10.0 0.0.0.255 10.10.40.0 0.0.0.255 log-input

access-list 100 permit ip any any

int fastethernet 0/1

ip access-group 100 in

We now repeat these steps for all the internal interfaces starting with fa1/0.

conf t

access-list 101 remark fromSoftDev

access-list 101 deny ip 10.10.200.0 0.0.0.255 10.10.10.0 0.0.0.255 log-input

access-list 101 deny ip 10.10.200.0 0.0.0.255 10.10.20.0 0.0.0.255 log-input

access-list 101 deny ip 10.10.200.0 0.0.0.255 10.10.30.0 0.0.0.255 log-input

access-list 101 deny ip 10.10.200.0 0.0.0.255 10.10.40.0 0.0.0.255 log-input

access-list 101 permit ip any any

int fastethernet 1/0

ip access-group 101 in

We also need to setup an ACL for sub-interface fa2/0.30

conf t

access-list 102 remark fromSales

access-list 102 deny ip 10.10.30.0 0.0.0.255 10.10.10.0 0.0.0.255 log-input

access-list 102 deny ip 10.10.30.0 0.0.0.255 10.10.200.0 0.0.0.255 log-input

access-list 102 deny ip 10.10.30.0 0.0.0.255 10.10.20.0 0.0.0.255 log-input

access-list 102 deny ip 10.10.30.0 0.0.0.255 10.10.40.0 0.0.0.255 log-input

access-list 102 permit ip any any

int fastethernet 2/0.30

ip access-group 102 in

The next step will be to configure an ACL for sub-interface fa2/0.40

conf t

access-list 103 remark fromMarketing

access-list 103 deny ip 10.10.40.0 0.0.0.255 10.10.10.0 0.0.0.255 log-input

access-list 103 deny ip 10.10.40.0 0.0.0.255 10.10.200.0 0.0.0.255 log-input

access-list 103 deny ip 10.10.40.0 0.0.0.255 10.10.20.0 0.0.0.255 log-input

access-list 103 deny ip 10.10.40.0 0.0.0.255 10.10.30.0 0.0.0.255 log-input

access-list 103 permit ip any any

int fastethernet 2/0.40

ip access-group 103 in

With those ACLs in place our internal network will be fairly secure. The ACLs we put in place will make it impossible to directly access the other networks. Yet, it will still be possible to connect to the Internet or to the DMZ.

Firewall configuration (PIX)

Now on the external firewall (PIX), we need to do some basic configurations.

conf t

enable password Cisco1

int ethernet 0

description toInternal

nameif inside

security-level 100

ip address 10.0.0.2 255.255.255.252

no shut

int ethernet 1

description toDMZ_Router

nameif DMZ

security-level 50

ip address 192.168.0.1 255.255.255.252

no shut

int ethernet 4

description toISP_Router

nameif outside

security-level 0

ip address 192.168.0.5 255.255.255.252

no shut

We will now enable the routing between the different interfaces. Again with an administrative distance of 250. Note also how all internal destinations are within the 10.0.0.0/8 network and we can therefore use route summarization:

route outside 0.0.0.0 0.0.0.0 192.168.0.6 250

route inside 10.0.0.0 255.0.0.0 10.0.0.1 250

route DMZ 172.16.100.0 255.255.255.0 192.168.0.2 250

To enable ICMP (ping) traffic from the inside interface to the DMZ we also need to put in place the following access list and attach it inbound to the DMZ interface.

access-list ICMP permit icmp any any

access-group ICMP in interface DMZ

RouterDMZ

Next up is the Router that connects the DMZ to the PIX firewall. We will establish static routing and some minor security features:

conf t

enable secret Cisco1

service password-encryption

username admin password administrator

ip domain-name noob.net

crypto key generate rsa [1024]

banner # Access to permitted personel only. #

banner motd # Trespassers will be prosecuted.#

line vty 0 5

transport input ssh

motd-banner

login local

line con 0

motd-banner

login local

int fastEthernet 0/0

description to PIX_FW

ip address 192.168.0.2 255.255.255.252

int fastEthernet 0/1

description to_DMZ

ip address 172.16.100.2 255.255.255.0

ip route 0.0.0.0 0.0.0.0 192.168.0.1 250

Router_ISP

conf t

enable secret Cisco1

service password-encryption

username admin password administrator

ip domain-name noob.net

crypto key generate rsa [1024]

banner # Access to permitted personel only. #

banner motd # Trespassers will be prosecuted.#

line vty 0 5

transport input ssh

motd-banner

login local

line con 0

motd-banner

login local

interface fastethernet 0/0

description to_PIX_FW

ip address 192.168.0.6 255.255.255.252

interface fastEthernet 0/1

description INTERNET

ip address 192.168.10.2 255.255.255.0

ip route 10.0.0.0 255.0.0.0 192.168.0.5 250

ip route 172.16.100.0 255.255.255.0 192.168.0.5 250

Short summary:

We built a DMZ network were traffic can flow from each VLAN to the outside. Yet, any IP traffic between the VLANS is blocked by ACLs.

The VLANs also can connect to the DMZ, but not vice versa.

The DMZ can connect to the outside.

The Outside is not able to reach the anything.

Static routing as a backup measure is in place, but will be upgraded by OSPF in the next post.

If you got any questions or need clarification on something, feel free to ask.

Cheers,

Manuel

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