Configuration of Security Contexts

Deployment Scenarios

The virtual firewall solution is useful in deployments where multiple firewalls are needed to protect traffic to and from the trusted networks. Although virtual firewalls can be deployed in many ways, for ease of understanding, we cover two design scenarios:

• Virtual firewall using two customer contexts
• Virtual firewall using a shared interface

Note

The design scenarios discussed in this section are used solely to reinforce learning. They should be used for reference purposes only.

 

Virtual Firewall Using Two Customer Contexts

SecureMe has an office in Brussels that provides firewall services to two small companies, Cubs and Bears. SecureMe's office is located in the same building as the offices of these companies. Cubs and Bears have specific requirements that SecureMe is obliged to meet. However, the appliance in Brussels has two active physical interfaces and, as a result, SecureMe wants to use subinterfaces to accommodate these customers. To conserve public addresses on the outside interfaces, the administrator uses a subnet mask of 255.255.255.248. Figure 9-5 shows SecureMe's new topology that will be set up in Brussels.

Figure 9-5. SecureMe Brussels Multimode Topology

The security requirements for SecureMe, along with Cubs and Bears, are as follows:

SecureMe security requirements:

• For SSH and Telnet user authentication, use a AAA server.
• Log all the system-generated messages to a syslog server.

Cubs security requirements:

• All hosts on 192.168.10.0/24 should be able to access the Internet.
• The source IP address should be translated to 209.165.200.230 using PAT.
• Allow HTTP clients from the Internet to access Cub's web server (192.168.5.10) on the DMZ network. This address should appear as 209.165.200.231 for the Internet users.
• Deny and log all other inbound traffic on the outside interface.

Bears security requirements:

• Allow hosts on the 192.168.20.0/24 subnet to access www.cisco.com only. All other web traffic should be blocked.
• The source IP address should be translated to 209.165.201.10 using interface PAT.
• Block and log all inbound traffic on the outside interface.

Example 9-17 shows the relevant configuration to achieve the goals just listed.

Example 9-17. ASA's Relevant Configuration with Multiple Security Contexts

 System Execution Space

Brussels# show run

ASA Version 7.0(1) 

! Main GigabitEthernet0/0 interface

interface GigabitEthernet0/0

! Sub-interface assigned to the admin context as the inside interface. A VLAN ID is

 !assigned to the interface

interface GigabitEthernet0/0.1

 vlan 5

! Sub-interface assigned to the Cubs context as the inside interface. A VLAN ID is

 !assigned to the interface

interface GigabitEthernet0/0.2

 vlan 10

! Sub-interface assigned to the Bears context as the inside interface. A VLAN ID is

 !assigned to the interface

interface GigabitEthernet0/0.3

 vlan 20

! Main GigabitEthernet0/1 interface

interface GigabitEthernet0/1



! Sub-interface assigned to the admin context as the outside interface. A VLAN ID

 is !assigned to the interface

interface GigabitEthernet0/1.1

 vlan 101

! Sub-interface assigned to the Cubs context as the outside interface. A VLAN ID is

 !assigned to the interface

interface GigabitEthernet0/1.2

 vlan 110

! Sub-interface assigned to the Bears context as the outside interface. A VLAN ID

 is !assigned to the interface

interface GigabitEthernet0/1.3

 vlan 120

! Sub-interface assigned to the Cubs context as the DMZ interface. A VLAN ID is

 !assigned to the interface

interface GigabitEthernet0/1.5

 vlan 130

!

hostname Brussels

! context named "admin" is the designated Admin context

admin-context admin

! "admin" context definition along with the allocated interfaces.

context admin

 description admin Context for admin purposes

 allocate-interface GigabitEthernet0/0.1

 allocate-interface GigabitEthernet0/1.1

 config-url disk0:/admin.cfg

! "Cubs" context definition along with the allocated interfaces.

context Cubs

 description Cubs Customer Context

 allocate-interface GigabitEthernet0/0.2

 allocate-interface GigabitEthernet0/1.2

 allocate-interface GigabitEthernet0/1.5

 config-url disk0:/Cubs.cfg

! "Bears" context definition along with the allocated interfaces.

context Bears

 description Bears Customer Context

 allocate-interface GigabitEthernet0/0.3

 allocate-interface GigabitEthernet0/1.3

 config-url disk0:/Bears.cfg

______________________________________________________________________________

 Admin Context

Brussels/admin# show running

ASA Version 7.0(1) 

!inside interface of the admin context with security level set to 100

interface GigabitEthernet0/0.1

 nameif inside

 security-level 100

 ip address 192.168.1.1 255.255.255.0

!outside interface of the admin context with security level set to 0

interface GigabitEthernet0/1.1

 nameif outside

 security-level 0

 ip address 209.165.202.130 255.255.255.248

!

hostname admin

!configuration of a syslog server with logging level set to emergencies with

 timestamp

logging enable

logging timestamp

logging trap emergencies

logging host inside 192.168.1.10

!

route outside 0.0.0.0 0.0.0.0 209.165.202.129 1

!configuration of a AAA server using RADIUS for authentication

aaa-server uauth protocol radius

aaa-server uauth host 192.168.1.20

 key cisco123

!setting up telnet and SSH authentication

aaa authentication telnet console uauth

aaa authentication ssh console uauth

!Telnet to the admin context is allowed from the inside interface

telnet 192.168.1.0 255.255.255.0 inside

telnet timeout 5

!SSH to the admin context is allowed from the outside interface

ssh 0.0.0.0 0.0.0.0 outside

ssh timeout 5

______________________________________________________________________________

 Cubs Context

Brussels/Cubs# show running

ASA Version 7.0(1) 

!inside interface of the Cubs context with security level set to 100

interface GigabitEthernet0/0.2

 nameif inside

 security-level 100

 ip address 192.168.10.1 255.255.255.0

!outside interface of the Cubs context with security level set to 0

interface GigabitEthernet0/1.2

 nameif outside

 security-level 0

 ip address 209.165.200.225 255.255.255.248

!DMZ interface of the Cubs context with security level set to 50

interface GigabitEthernet0/1.5

 nameif dmz

 security-level 50

 ip address 192.168.5.1 255.255.255.0

!

hostname Cubs

!Access-list configuration to allow web traffic. The access-list is applied to the

 outside interface.

access-list outside-in extended permit tcp any host 209.165.200.231 eq www

access-list outside-in extended deny ip any any log

access-group outside-in in interface outside

!NAT configuration to allow inside hosts to get Internet connectivity

global (outside) 1 209.165.200.230

nat (inside) 1 192.168.10.0 255.255.255.0



!Static address translation for the Web-Server

static (dmz,outside) 209.165.200.231 192.168.5.10 netmask 255.255.255.255

!

route outside 0.0.0.0 0.0.0.0 209.165.200.226 1

______________________________________________________________________________

 Bears Context

Brussels/Bears# show running

ASA Version 7.0(1) 

!inside interface of the Bears context with security level set to 100

interface GigabitEthernet0/0.3

 nameif inside

 security-level 100

 ip address 192.168.20.1 255.255.255.0

!outside interface of the Bears context with security level set to 0

interface GigabitEthernet0/1.3

 nameif outside

 security-level 0

 ip address 209.165.201.2 255.255.255.224

!

enable password 8Ry2YjIyt7RRXU24 encrypted

passwd 2KFQnbNIdI.2KYOU encrypted

hostname Bears

!Access-list configuration to permit web traffic initiated from the inside host and

 destined to 198.133.219.25. Deny all other traffic. The access-list is applied

 to the inside interface.

access-list inside-in extended permit tcp 192.168.20.0 255.255.255.0 host

198.133.219.25 eq 80

access-group inside-in in interface inside

!Access-list configuration to deny and log all inbound traffic. The access-list is

 applied to the outside interface

access-list outside-in extended deny ip any any log

access-group outside-in in interface outside

!NAT configuration to allow inside hosts to get Internet connectivity

global (outside) 1 interface

nat (inside) 1 192.168.20.0 255.255.255.0

!

route outside 0.0.0.0 0.0.0.0 209.165.201.1 1

 

Virtual Firewall Using a Shared Interface

An educational institute contacts SecureMe to provide firewall services for two of its departmentsfaculty and studentsover a shared outside interface. The hosts in the student context are allowed to access a web server in the faculty context. Additionally, they are allowed to check their e-mail messages from 209.165.202.130. The faculty context, on the other hand, does not restrict anything going out to the Internet.

The SecureMe global policy restricts access of the security appliance to the valid and authorized users on the AAA servers. SecureMe does not have many public addresses available, so it is using interface PAT for address translation. Additionally, SecureMe does not want the administrators of the individual security contexts to be able to determine the interface assignment for their contexts. Figure 9-6 shows SecureMe's proposed topology for this institute.

Figure 9-6. Security Contexts Using a Shared Interface

Example 9-18 shows the relevant configuration for the Cisco ASA used in this deployment.

Example 9-18. ASA's Relevant Configuration Using a Shared Outside Interface

 System Execution Space

SecuremeInstitute# show run

ASA Version 7.0(1) 

! Main GigabitEthernet0/0 interface

interface GigabitEthernet0/0



! Sub-interface assigned to the admin context as the inside interface. A VLAN ID is

 !assigned to the interface

interface GigabitEthernet0/0.1

 vlan 5

! Sub-interface assigned to the Students context as the inside interface. A VLAN ID

 is !assigned to the interface

interface GigabitEthernet0/0.2

 vlan 10

! Sub-interface assigned to the Faculty context as the inside interface. A VLAN ID

 is !assigned to the interface

interface GigabitEthernet0/0.3

 vlan 20

! Main GigabitEthernet0/1 interface to be used as the shared interface

interface GigabitEthernet0/1

!

hostname SecuremeInstitute

! context named "admin" is the designated Admin context

admin-context admin

! "admin" context definition along with the allocated interfaces.

context admin

 description admin Context for admin purposes

 allocate-interface GigabitEthernet0/0.1 inside invisible

 allocate-interface GigabitEthernet0/1 outside invisible

 config-url disk0:/admin.cfg

! "Students" context definition along with the allocated interfaces.

context Students

 description Students Customer Context

 allocate-interface GigabitEthernet0/0.2 S_inside invisible

 allocate-interface GigabitEthernet0/1 S_outside invisible

 config-url disk0:/Students.cfg

! "Faculty" context definition along with the allocated interfaces.

context Faculty

 description Faculty Customer Context

 allocate-interface GigabitEthernet0/0.3 F_inside invisible

 allocate-interface GigabitEthernet0/1 F_outside invisible

 config-url disk0:/Faculty.cfg

________________________________________________________________________

 Admin Context

SecuremeInstitute/admin# show running

ASA Version 7.0(1) 

!inside interface of the admin context with security level set to 100

interface inside

 nameif inside

 security-level 100

 ip address 192.168.1.1 255.255.255.0

!outside interface of the admin context with security level set to 0

interface outside

 nameif outside

 security-level 0

 ip address 209.165.200.225 255.255.255.224

!

hostname admin

!

route outside 0.0.0.0 0.0.0.0 209.165.200.230 1

!configuration of a AAA server using RADIUS for authentication

aaa-server uauth protocol radius

aaa-server uauth host 192.168.1.20

 key cisco123

aaa authentication telnet console uauth

aaa authentication ssh console uauth

!Telnet to the admin context is allowed from the inside interface

telnet 192.168.1.0 255.255.255.0 inside

telnet timeout 5

!SSH to the admin context is allowed from the outside interface

ssh 0.0.0.0 0.0.0.0 outside

ssh timeout 5

route outside 0.0.0.0 0.0.0.0 209.165.200.225 1

_________________________________________________________________________

 Students Context

SecuremeInstitute/Students# show running

ASA Version 7.0(1) 

!inside interface of the Students context with security level set to 100

interface S_inside

 nameif inside

 security-level 100

 ip address 192.168.10.1 255.255.255.0

!outside interface of the Students context with security level set to 0

interface S_outside

 nameif outside

 security-level 0

 ip address 209.165.200.226 255.255.255.224

!Access-list configuration to allow email and web traffic. The access-list is

 applied to the inside interface.

access-list inside-in extended permit tcp 192.168.10.0 255.255.255.0 host

 209.165.202.130 eq smtp

access-list inside-in extended permit tcp 192.168.10.0 255.255.255.0 host

 209.165.200.230 eq www

access-group inside-in in interface S_inside

!

hostname Students

!NAT configuration to allow inside hosts to get Internet connectivity

global (S_outside) 1 interface

nat (S_inside) 1 192.168.10.0 255.255.255.0

!

route S_outside 0.0.0.0 0.0.0.0 209.165.200.225 1

___________________________________________________________________________

 Faculty Context

SecuremeInstitute/Faculty# show running

ASA Version 7.0(1) 

!inside interface of the Faculty context with security level set to 100

interface F_inside

 nameif inside

 security-level 100

 ip address 192.168.20.1 255.255.255.0

!outside interface of the Faculty context with security level set to 0

interface F_outside

 nameif outside

 security-level 0

 ip address 209.165.200.227 255.255.255.224

!

enable password 8Ry2YjIyt7RRXU24 encrypted

passwd 2KFQnbNIdI.2KYOU encrypted

hostname Faculty

!Access-list configuration to allow web traffic. The access-list is applied to the

 outside interface.

access-list outside-in extended permit tcp host 209.165.200.226 host 209.165.200.230

eq www

access-group outside-in in interface F_outside

!NAT configuration to allow inside hosts to get Internet connectivity

global (F_outside) 1 interface

nat (F_inside) 1 192.168.20.0 255.255.255.0

!Static address translation for the Web-Server

static (F_inside,F_outside) 209.165.200.230 192.168.20.20 netmask 255.255.255.255

!

route F_outside 0.0.0.0 0.0.0.0 209.165.200.225 1