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14.1 - Current Release 13.1 13.0 12.1
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Use case 11: Isolating network traffic using listen policies

September 14, 2021
Contributed by: 
S C

Note

The traffic isolation solution using shadow virtual servers to simulate multitenant isolation is no more recommended. Alternatively, Citrix recommends you to use the Citrix ADC Admin Partitioning feature for such deployments. For more information, see Admin Partitioning.

A common security requirement in a data center is to maintain network path isolation between the traffic of various applications or tenants. One application or tenant’s traffic must be isolated from the traffic of other applications or tenants. For example, a financial services company would want to keep the traffic of its insurance department’s applications separate from that of its financial services applications. In the past, this was easily achieved through physical separation of network service devices such as firewalls, load balancers, and IdP, and network monitoring and logical separation in the switching fabric.

As data center architectures evolve toward multitenant virtualized data centers, networking services in the aggregation layer of a data center are getting consolidated. This development has made network path isolation a critical component for network service devices and is driving the requirement for ADCs to be able to isolate traffic at the L4 to L7 levels. Furthermore, all the traffic of a particular tenant must go through a firewall before reaching the service layer.

To address the requirement of isolating the network paths, a Citrix ADC appliance identifies the network domains and controls the traffic across the domains. The Citrix ADC solution has two main components: listen policies and shadow virtual servers.

Each network path to be isolated is assigned a virtual server on which a listen policy is defined so that the virtual server listens to traffic only from a specified network domain.

To isolate the traffic, listen policies can be based on several client parameters or their combinations, and the policies can be assigned priorities. The following table lists the parameters that can be used in listen policies for identifying the traffic.

Category Parameters
Ethernet protocol Source MAC address, destination MAC address
Network interface Network ID, receiving throughput, sending throughput, transmission throughput
IP protocol Source IP address, destination IP address
IPv6 protocol Source IPv6 address, destination IPv6 address
TCP protocol Source port, destination port, maximum segment size, payload, and other options
UDP protocol Source port, destination port
VLAN ID

Table 1. Client Parameters Used to Define Listen Policies

On the Citrix ADC appliance, a virtual server is configured for each domain, with a listen policy specifying that the virtual server is to listen only to traffic for that domain. Also configured for each domain is a shadow load balancing virtual server, which listens to traffic destined for any domain. Each of the shadow load balancing virtual servers has a wildcard (*) IP address and port, and its service type is set to ANY.

In each domain, a firewall for the domain is bound as a service to the shadow load balancing virtual server, which forwards all traffic through the firewall. Local traffic is forwarded to its destination, and traffic destined for another domain is forwarded to the firewall for that domain. The shadow load balancing virtual servers are configured for MAC mode redirection.

How network paths are isolated

The following figure shows a typical traffic flow across domains. Consider the traffic flow within Network Domain 1, and between Network Domain 1 and Network Domain 2.

Figure 1. Isolating Network Path

Traffic Domains - Network Path Isolation

Traffic within network domain 1

Network Domain 1 has three VLANs: VLAN 11, VLAN110, and VLAN120. The following steps describe the traffic flow.

  • A client from VLAN 11 sends a request for a service available from the service pool in VLAN 120.
  • The load balancing virtual server LB-VIP1, which is configured to listen to traffic from VLAN 11, receives the request and forwards the request to VLAN 110. The virtual server in VLAN 110 forwards the request to shadow load balancing virtual server FW-VIP-1.
  • FW-VIP-1, which is configured to listen to traffic from VLAN 110, receives the request and forwards it to VLAN 120.
  • The load balancing virtual server in VLAN 120 load balances the request to one of the physical servers, App11, App12, or App13.
  • The response sent by the physical server returns by the same path to the client in VLAN 11.

This configuration ensures that traffic is always segregated inside the Citrix ADC for all the traffic that originates from a client.

Traffic between network domain 1 and network domain 2

Network Domain 1 has three VLANs: VLAN 11, VLAN 110, and VLAN 120. Network Domain 2 also has three VLANS: VLAN 22, VLAN 210, and VLAN 220. The following steps describe the traffic flow from VALN 11 to VLAN 22.

  • A client from VLAN 11, which belongs to Network Domain 1, sends a request for a service available from the service pool in VLAN 220, which belongs to the Network Domain 2.
  • In Network Domain 1, the load balancing virtual server LB-VIP1, which is configured to listen to traffic from VLAN 11, receives the request and forwards the request to VLAN 110.
  • Shadow load balancing virtual server FW-VIP-1, which is configured to listen to VLAN 110 traffic destined to any other domain, receives the request and forwards it to firewall virtual server FW-VIP-2 because the request is destined to a physical server in Network Domain 2.
  • In Network Domain 2, FW-VIP-2 forwards the request to VLAN 220.
  • The load balancing virtual server in VLAN 220 load balances the request to one of the physical servers, App21, App22, or App23.
  • The response sent by the physical server returns by the same path through the firewall in Network Domain 2 and then to Network Domain 1 to reach the client in VLAN 11.

Configuration Steps

To configure network path isolation by using listen policies, do the following:

  • Add listen policy expressions. Each expression specifies a domain to which traffic is destined. You can use the VLAN ID or other parameters to identify the traffic.
  • For each network domain, configure two virtual servers as follows:

    • Create a load balancing virtual server for which you specify a listen policy that identifies the traffic destined for this domain. You can specify the name of an expression created earlier, or you can create an expression while creating the virtual server.

    • Create another load balancing virtual server, referred to as shadow virtual server, for which you specify a listen policy expression that applies to traffic destined for any domain. On this virtual server, set the service type to ANY and the IP address and port to an asterisk (*). Enable MAC-based forwarding on this virtual server.

    • Enable the L2 Connection option on both the virtual servers.

      Generally, to identify a connection, the Citrix ADC appliance uses the 4-tuple of client IP address, client port, destination IP address, and destination port. When you enable the L2 Connection option, the Layer 2 parameters of the connection (channel number, MAC address, and VLAN ID) are used in addition to the normal 4-tuple.

  • Add services representing the server pools in the domain, and bind them to the virtual server.
  • Configure the firewall for each domain as a service, and bind all the firewall services to the shadow virtual server.

To isolate network traffic by using the command line interface

At the command prompt, type the following commands:

add policy expression <expressionName> <listenPolicyExpression>

add lb vserver <name> <serviceType> <ip> <port> -l2conn ON -listenPolicy <expressionName>
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Add a load balancing virtual server for each domain. This virtual server is for traffic of the same domain.

add lb vserver <name> ANY * * -l2conn ON -m MAC -listenPolicy <expressionName>
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Add a shadow load balancing virtual server for each domain. This virtual server is for traffic of other domains.

Example:

add policy expression e110 client.vlan.id==110
add policy expression e210 client.vlan.id==210
add policy expression e310 client.vlan.id==310
add policy expression e11 client.vlan.id==11
add policy expression e22 client.vlan.id==22
add policy expression e33 client.vlan.id==33

add lb vserver LB-VIP1 HTTP 10.1.1.254 80 -persistenceType NONE -listenPolicy e11
-cltTimeout 180 -l2Conn ON

add lb vserver LB-VIP2 HTTP 10.2.2.254 80 -persistenceType NONE - listenPolicy e22
-cltTimeout 180 -l2Conn ON

add lb vserver LB-VIP3 HTTP 10.3.3.254 80 -persistenceType NONE - listenPolicy e33
-cltTimeout 180 -l2Conn ON


add lb vserver FW-VIP-1 ANY * * -persistenceType NONE -lbMethod ROUNDROBIN - listenPolicy e110 -Listenpriority 1 -m MAC -cltTimeout 120

add lb vserver FW-VIP-2 ANY * * -persistenceType NONE -lbMethod ROUNDROBIN - listenPolicy e210 -Listenpriority 2 -m MAC -cltTimeout 120

add lb vserver FW-VIP-3 ANY * * -persistenceType NONE -lbMethod ROUNDROBIN - listenPolicy e310 -Listenpriority 3 -m MAC -cltTimeout 120


add service RD-1 10.1.1.1 ANY * -gslb NONE -maxClient 0 -maxReq 0 -cip DISABLED
-usip NO -useproxyport NO -sp ON -cltTimeout 120 -svrTimeout 120 -CKA NO -TCPB NO -CMP NO

add service RD-2 10.2.2.1 ANY * -gslb NONE -maxClient 0 -maxReq 0 -cip DISABLED
-usip NO -useproxyport NO -sp ON -cltTimeout 120 -svrTimeout 120 -CKA NO -TCPB NO -CMP NO

add service RD-3 10.3.3.1 ANY * -gslb NONE -maxClient 0 -maxReq 0 -cip DISABLED
-usip NO -useproxyport NO -sp ON -cltTimeout 120 -svrTimeout 120 -CKA NO -TCPB NO -CMP NO


bind lb vserver FW-VIP-1 RD-1

bind lb vserver FW-VIP-2 RD-2

bind lb vserver FW-VIP-3 RD-3
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To isolate network traffic by using the configuration utility

  1. Add services representing the servers, as described in Creating a Service.
  2. Add each firewall as a service:
    1. Navigate to Traffic Management > Load Balancing > Services.
    2. Create a service, specifying the protocol as ANY, server as firewall’s IP address, and port as 80.
  3. Configure a load balancing virtual server.
  4. Configure the shadow load balancing virtual server.
  5. For each network domain, repeat steps 3 and 4.
  6. From the Load Balancing Virtual Servers pane, open the virtual servers that you created and verify the settings.
Use case 11: Isolating network traffic using listen policies
September 14, 2021
Contributed by: 
S C
September 14, 2021
Contributed by: 
S C

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