Catalyst 6500 Series Switch Content Switching Module with SSL (CSM-S) Installation and Configuration Note - Configuring Firewall Load Balancing [Cisco Services Modules]

Table Of Contents

Configuring Firewall Load Balancing

Understanding How Firewalls Work

Firewall Types

How the CSM-S Distributes Traffic to Firewalls

Supported Firewalls

Layer 3 Load Balancing to Firewalls

Types of Firewall Configurations

IP Reverse-Sticky for Firewalls

CSM-S Firewall Configurations

Fault-Tolerant CSM-S Firewall Configurations

Configuring Stealth Firewall Load Balancing

Stealth Firewall Configuration

Stealth Firewall Configuration Example

Configuring CSM-S A (Stealth Firewall Example)

Configuring CSM-S B (Stealth Firewall Example)

Configuring Regular Firewall Load Balancing

Packet Flow in a Regular Firewall Configuration

Regular Firewall Configuration Example

Configuring CSM-S A (Regular Firewall Example)

Configuring CSM-S B (Regular Firewall Example)

Configuring Reverse-Sticky for Firewalls

Understanding Reverse-Sticky for Firewalls

Configuring Reverse-Sticky for Firewalls

Configuring Stateful Firewall Connection Remapping

Configuring Firewall Load Balancing

This chapter describes how to configure firewall load balancing and contains these sections:

•Understanding How Firewalls Work

•Configuring Stealth Firewall Load Balancing

•Configuring Regular Firewall Load Balancing

•Configuring Reverse-Sticky for Firewalls

•Configuring Stateful Firewall Connection Remapping

Firewall load balancing allows you to scale firewall protection by distributing traffic across multiple firewalls on a per-connection basis. All packets belonging to a particular connection must go through the same firewall. The firewall then allows or denies transmission of individual packets across its interfaces.

Understanding How Firewalls Work

A firewall forms a physical barrier between two parts of a network, for example, the Internet and an intranet. When a firewall accepts a packet from one side (the Internet), it sends the packet through to the other side (the intranet). A firewall can modify a packet before passing it through or sending it through unaltered. When a firewall rejects a packet, it usually drops the packet and logs the dropped packet as an event.

After a session is established and a flow of packets begins, a firewall can monitor each packet in the flow or allow the flow to continue, unmonitored, depending on the policies that are configured on that firewall.

This section contains the following:

•Firewall Types

•How the CSM-S Distributes Traffic to Firewalls

•Supported Firewalls

•Layer 3 Load Balancing to Firewalls

•Types of Firewall Configurations

•IP Reverse-Sticky for Firewalls

•CSM-S Firewall Configurations

•Fault-Tolerant CSM-S Firewall Configurations

Firewall Types

The two basic types of firewalls are as follows:

•Regular firewalls

•Stealth firewalls

Regular firewalls have a presence on the network; they are assigned an IP address that allows them to be addressed as a device and seen by other devices on the network.

Stealth firewalls have no presence on the network; they are not assigned an IP address and cannot be addressed or seen by other devices on the network. To the network, a stealth firewall is part of the wire.

Both firewall types examine traffic moving in both directions (between the protected and the unprotected side of the network) and accept or reject packets based on user-defined sets of policies.

How the CSM-S Distributes Traffic to Firewalls

The CSM-S load balances traffic to devices configured in server farms. These devices can be servers, firewalls, or any IP-addressable object including an alias IP address. The CSM-S uses load-balancing algorithms to determine how the traffic is balanced among the devices configured in server farms, independent of device type.

Note We recommend that you configure Layer 3 load balancing on server farms that contain firewalls because of the interactions between higher-layer load-balancing algorithms and server applications.

Supported Firewalls

The CSM-S can load balance traffic to regular or stealth firewalls.

For regular firewalls, a single CSM-S or a pair of CSMs balances traffic among firewalls that contain unique IP addresses, similar to how the CSM-S balances traffic to servers.

For stealth firewalls, a CSM-S balances traffic among unique VLAN alias IP address interfaces on another CSM-S that provides paths through stealth firewalls. A stealth firewall is configured so that all traffic moving in both directions across that VLAN moves through the firewall.

Layer 3 Load Balancing to Firewalls

When the CSM-S load balances traffic to firewalls, the CSM-S performs the same function that it performs when it load balances traffic to servers. To configure Layer 3 load balancing to firewalls, follow these steps:

Step 1 Create a server farm for each side of the firewall.

Step 2 In serverfarm submode, enter the predictor hash address command.

Step 3 Assign that server farm to the virtual server that accepts traffic destined for the firewalls.

Note When you configure Layer 3 load balancing to firewalls, use source NAT in the forward direction and destination NAT in the reverse direction.

Types of Firewall Configurations

The CSM-S supports these two firewall configuration types:

•Dual-CSM-S configuration—Firewalls are located between two CSM modules. The firewalls accept traffic from one CSM-S and send it to a second CSM-S for load balancing to servers or return to the requesting device.

•Single-CSM-S configuration—Firewalls accept traffic from a CSM-S and send it back to the same CSM-S for load balancing to servers, or they can return traffic to the requesting device.

IP Reverse-Sticky for Firewalls

The CSM-S currently supports sticky connections. Sticky connections ensure that two distinct data flows originating from the same client are load balanced to the same destination.

Load-balanced destinations are often real servers. They may be firewalls, caches, or other networking devices. Sticky connections are necessary for the proper functioning of load-balanced applications. These applications utilize multiple connections from the same client to a server. The information transferred on one connection may affect the processing of information transferred on another connection.

The IP reverse-sticky feature is configured for balancing new connections from the same client to the same server, as described in the "Configuring Reverse-Sticky for Firewalls" section. This feature is especially important in the case of buddy connections, such as an FTP data channel or a streaming UDP data channel.

CSM-S Firewall Configurations

The CSM-S can support these firewall configurations:

•Stealth firewalls for dual CSM-S configurations (Figure 13-1)

•Regular firewalls for dual CSM-S configurations (Figure 13-2)

•Regular firewalls for single CSM-S configurations (Figure 13-3)

•Mixed firewalls (stealth and regular) for dual CSM-S configurations (Figure 13-4)

In Figure 13-1, traffic moves through the firewalls and is filtered in both directions. The figure shows the flow from the Internet to the intranet. On the path to the intranet, CSM-S A balances traffic across VLANs 5, 6, and 7 through firewalls to CSM-S B. On the path to the Internet, CSM-S B balances traffic across VLANs 15, 16, and 17 through firewalls to CSM-S A. CSM-S A uses the VLAN aliases of CSM-S B in its server farm, and CSM-S B uses the VLAN aliases of CSM-S A in its server farm.

Figure 13-1 Stealth Firewall Configuration (Dual CSM-S modules Only)

In Figure 13-2, traffic moves through the firewalls and is filtered in both directions. The figure shows the flow from the Internet to the intranet. VLANs 11 and 111 are on the same subnet, and
VLANs 12 and 112 are on the same subnet.

Figure 13-2 Regular Firewall Configuration (Dual CSM-S modules)

In Figure 13-3, traffic moves through the firewalls and is filtered in both directions. The figure shows only the flow from the Internet to the intranet, and VLANs 11 and 111 are on the same subnet.
VLANs 12 and 112 are on the same subnet.

Figure 13-3 Regular Firewall Configuration (Single CSM-S)

In Figure 13-4, traffic moves through both the regular and stealth firewalls and is filtered in both directions. The figure shows the flow from the Internet to the intranet. VLANs 5, 6, and 7 are shared between CSM-S A and CSM-S B. On the path to the intranet, CSM-S A balances traffic across VLANs 5, 6, and 7 through firewalls to CSM-S B. On the path to the intranet, CSM-S B balances traffic across VLANs 5, 6, and 7 through firewalls to CSM-S A.

Figure 13-4 Mixed Firewall Configuration for Stealth and Regular Firewalls (Dual CSM-S Only)

Fault-Tolerant CSM-S Firewall Configurations

The CSM-S supports fault tolerance for these configurations:

•Stealth firewalls in a fault-tolerant dual CSM-S configuration

•Regular firewalls in a fault-tolerant dual CSM-S configuration

•Regular firewalls in a fault-tolerant single CSM-S configuration

•Mixed firewalls (stealth and regular) in a fault-tolerant dual CSM-S configuration

In Figure 13-5, the traffic moves through the firewalls and is filtered in both directions. The figure only shows the flow from the Internet to the intranet through the primary CSMs, and VLANs 11 and 111 are on the same subnet. VLANs 12 and 112 are on the same subnet.

Figure 13-5 Fault-Tolerant, Regular Firewall Configuration-(Dual CSMs)

Configuring Stealth Firewall Load Balancing

This section describes how to configure firewall load balancing for stealth firewalls and covers the following information:

•Stealth Firewall Configuration

•Stealth Firewall Configuration Example

Stealth Firewall Configuration

In a stealth firewall configuration, firewalls connect to two different VLANs and are configured with IP addresses on the VLANs to which they connect. (See Figure 13-6.)

Figure 13-6 Stealth Firewall Configuration Example

Location

Traffic Direction

Arrives On

Exits On

1

To intranet

VLAN 10

VLANs 101 and 103

2

To intranet

VLANs 101 and 103

VLAN 20

3

To Internet

VLAN 20

VLANs 102 and 104

4

To Internet

VLANs 101 and 103

VLAN 10

Figure 13-6 shows two regular firewalls (Firewall 1 and Firewall 2) located between two CSM modules
(CSM-S A and CSM-S B).

Note Stealth firewalls do not have addresses on VLANs.

On the path from the Internet to the intranet, traffic enters the insecure side of the firewalls through separate VLANs, VLAN 101 and VLAN 103, and exits the secure side of the firewalls through separate VLANs, VLAN 102 and VLAN 104. On the path from the intranet to the Internet, the flow is reversed. VLANs also provide connectivity to the Internet (VLAN 10) and to the intranet (VLAN 20).

In a stealth configuration, CSM-S A and CSM-S B load balance traffic through the firewalls.

Stealth Firewall Configuration Example

The stealth firewall configuration example contains two CSM-S modules (CSM-S A and CSM-S B) installed in separate Catalyst 6500 series switches.

Note In a stealth firewall configuration, each CSM-S must be installed in a separate Catalyst 6500 series switch.

This section describes how to create the stealth firewall configuration for CSM-S A and CSM-S B.

Configuring CSM-S A (Stealth Firewall Example)

To create the regular configuration example, perform these tasks for CSM-S A:

•Creating VLANs on Switch A

•Configuring VLANs on CSM-S A

•Configuring Server Farms on CSM-S A

•Configuring Virtual Servers on CSM-S A

Note Although the configuration tasks are the same for both the CSM-S A and CSM-S B, the steps, commands, and parameters that you enter are different.

Creating VLANs on Switch A

To create two VLANs on Switch A, perform this task:
Command

Purpose
Step 1
Switch-A(config)# vlan 
Enters the VLAN mode¹.
Step 2
Switch-A(vlan)# vlan 10
Creates VLAN 10².
Step 3
Switch-A(vlan)# vlan 101
Creates VLAN 101³.
Step 4
Switch-A(vlan)# vlan 103
Creates VLAN 103⁴.
¹Perform this step on the switch console of the switch that contains CSM-S A.

²VLAN 10 connects CSM-S A to the Internet.

³VLAN 101 provides a connection through Firewall 1 to CSM-S B.

⁴VLAN 103 provides a connection through Firewall 2 to CSM-S B.
Configuring VLANs on CSM-S A

To configure the three VLANs, perform this task:
Command

Purpose
Step 1
Switch-A(config)# module csm 5
Enters multiple module configuration mode and specifies that CSM-S A is installed in slot 5.
Step 2
Switch-A(config-module-csm)# vlan 10 
client
Specifies VLAN 10 as the VLAN that is being configured, identifies it as a client VLAN, and enters VLAN configuration mode.
Step 3
Switch-A(config-slb-vlan-client)# ip 
address 10.0.1.35 255.255.255.0
Specifies an IP address and netmask for VLAN 10.
Step 4
Switch-A(config-slb-vlan-client)# alias 
10.0.1.30 255.255.255.0
Specifies an alias IP address and netmask for VLAN 10¹.
Step 5
Switch-A(config-slb-vlan-client)# exit
Returns to VLAN configuration mode.
Step 6
Switch-A(config-module-csm)# vlan 101 
server
Specifies VLAN 101 as the VLAN that is being configured, identifies it as a server VLAN, and enters VLAN configuration mode.
Step 7
Switch-A(config-slb-vlan-server)# ip 
address 10.0.101.35 255.255.255.0
Specifies an IP address and netmask for VLAN 101.
Step 8
Switch-A(config-slb-vlan-server)# alias 
10.0.101.100 255.255.255.0
Specifies an alias IP address and netmask for VLAN 1011.
Step 9
Switch-A(config-slb-vlan-server)# exit
Returns to VLAN configuration mode.
Step 10
Switch-A(config-module-csm)# vlan 103 
server
Specifies VLAN 103 as the VLAN that is being configured, identifies it as a server VLAN, and enters VLAN configuration mode.
Step 11
Switch-A(config-slb-vlan)# ip address 
10.0.102.35 255.255.255.0
Specifies an IP address and netmask for VLAN 103.
Step 12
Switch-A(config-slb-vlan)# alias 
10.0.102.100 255.255.255.0
Specifies an alias IP address and netmask for VLAN 1031.
¹This step provides a target for CSM-S B to use in making a load-balancing decision.
Configuring Server Farms on CSM-S A

Note Because the IP addresses of CSM-S B are listed in the INSIDE-SF server farm as real servers, CSM-S A will load balance the two firewalls that exist in the path to CSM-S B.

To configure two server farms on CSM-S A, perform this task:
Command

Purpose
Step 1
Switch-A(config)# module csm 5
Enters multiple module configuration mode and specifies that CSM-S A is installed in slot 5.
Step 2
Switch-A(config-module-csm)# serverfarm 
FORWARD-SF
Creates and names the FORWARD-SF¹ server farm (actually a forwarding policy) and enters serverfarm configuration mode.
Step 3
Switch-A(config-slb-sfarm)# no nat server
Disables the NAT of server IP addresses and port numbers².
Step 4
Switch-A(config-slb-sfarm)# predictor 
forward
Forwards traffic in accordance with its internal routing tables rather than a load-balancing algorithm.
Step 5
Switch-A(config-slb-sfarm)# exit
Returns to multiple module configuration mode.
Step 6
Switch-A(config-module-csm)# serverfarm 
TO-INSIDE-SF
Creates and names the INSIDE-SF³ server farm (that will contain alias IP addresses rather than real servers) and enters serverfarm configuration mode.
Step 7
Switch-A(config-slb-sfarm)# no nat server
Disables the NAT of the server IP address and port number⁴.
Step 8
Switch-A(config-slb-sfarm)# predictor 
hash address source 255.255.255.255
Selects a server using a hash value based on the source IP address⁵.
Step 9
Switch-A(config-slb-sfarm)# real 
10.0.101.200
Identifies the alias IP address of CSM-S B that lies on the path to Firewall 1 as a real server and enters real server configuration submode.
Step 10
Switch-A(config-slb-real)# inservice
Enables the firewall.
Step 11
Switch-A(config-slb-real)# exit
Returns to serverfarm configuration mode.
Step 12
Switch-A(config-slb-sfarm)# real 
10.0.102.200
Identifies the alias IP address of CSM-S B that lies on the path to Firewall 2 as a real server and enters real server configuration submode.
Step 13
Switch-A(config-slb-real)# inservice
Enables the firewall.
¹FORWARD-SF is actually a route forwarding policy, not an actual server farm, that allows traffic to reach the Internet (through VLAN 10). It does not contain any real servers.

²This step is required when configuring a server farm that contains a forwarding policy rather than real servers.

³INSIDE-SF contains the two alias IP addresses of CSM-S B listed as real servers that allow traffic from the intranet to reach CSM-S B.

⁴This step is required when configuring a server farm that contains firewalls.

⁵We recommend that you perform this step when configuring insecure-side firewall interfaces in a server farm.
Configuring Virtual Servers on CSM-S A

To configure three virtual servers on CSM-S A, perform this task:
Command

Purpose
Step 1
Switch-A(config)# module csm 5
Enters multiple module configuration mode and specifies that the CSM-S A is installed in slot 5.
Step 2
Switch-A(config-module-csm)# vserver 
FORWARD-V101
Specifies FORWARD-V101¹ as the virtual server that is being configured and enters virtual server configuration mode.
Step 3
Switch-A(config-slb-vserver)# virtual 
0.0.0.0 0.0.0.0 any
Specifies a match for any IP address and any protocol².
Step 4
Switch-A(config-slb-vserver))# vlan 101
Specifies that the virtual server will only accept traffic arriving on VLAN 101, which is traffic arriving from the insecure side of the firewalls.
Step 5
Switch-A(config-slb-vserver)# serverfarm 
FORWARD-SF
Specifies the server farm for this virtual server³.
Step 6
Switch-A(config-slb-vserver)# inservice
Enables the virtual server.
Step 7
Switch-A(config-slb-vserver)# exit
Returns to multiple module configuration mode.
Step 8
Switch-A(config-module-csm)# vserver 
FORWARD-V103
Specifies FORWARD-V103⁴ as the virtual server that is being configured and enters virtual server configuration mode.
Step 9
Switch-A(config-slb-vserver)# virtual 
0.0.0.0 0.0.0.0 any
Specifies a match for any IP address and any protocol⁵.
Step 10
Switch-A(config-slb-vserver))# vlan 103
Specifies that the virtual server will only accept traffic arriving on VLAN 103, which is traffic arriving from the insecure side of the firewalls.
Step 11
Switch-A(config-slb-vserver)# serverfarm 
FORWARD-SF
Specifies the server farm for this virtual server3.
Step 12
Switch-A(config-slb-vserver)# inservice
Enables the virtual server.
Step 13
Switch-A(config-slb-vserver)# exit
Returns to multiple module configuration mode.
Step 14
Switch-A(config-module-csm)# vserver 
OUTSIDE-VS
Specifies OUTSIDE-VS⁶ as the virtual server that is being configured and enters virtual server configuration mode.
Step 15
Switch-A(config-slb-vserver)# virtual 
10.1.0.0 255.255.255.0 any
Specifies the IP address, netmask, and protocol (any) for this virtual server. Clients reach the server farm represented by this virtual server through this address.
Step 16
Switch-A(config-slb-vserver))# vlan 10
Specifies that the virtual server will only accept traffic arriving on VLAN 10, which is traffic arriving from the Internet.
Step 17
Switch-A(config-slb-vserver)# serverfarm 
TO-INSIDE-SF
Specifies the server farm for this virtual server⁷.
Step 18
Switch-A(config-slb-vserver)# inservice
Enables the virtual server.
¹FORWARD-V101 allows Internet traffic to reach the insecure side of the firewalls (through VLAN 101).

²Client matching is only limited by VLAN restrictions. (See Step 4.)

³This server farm is actually a forwarding predictor rather than an actual server farm containing real servers.

⁴FORWARD-V103 allows Internet traffic to reach the insecure side of the firewalls (through VLAN 103).

⁵Clients will always match (see Step 9)-only being limited by VLAN restrictions. (See Step 10.)

⁶OUTSIDE-VS allows traffic from the Internet to reach CSM-S A (through VLAN 10).

⁷The server farm contains the alias IP addresses of CSM-S B that lie along the path of Firewall 1 and Firewall 2.
Configuring CSM-S B (Stealth Firewall Example)

To create the regular configuration example, perform the following configuration tasks for CSM-S B:

•Creating VLANs on Switch B

•Configuring VLANs on CSM-S B

•Configuring Server Farms on CSM-S B

•Configuring Virtual Servers on CSM-S B

Note Although the configuration tasks are the same for both CSM-S A and CSM-S B, the steps, commands, and parameters that you enter are different.

Creating VLANs on Switch B

To create three VLANs on Switch B, perform this task:

Note This example assumes that the CSM-S modules are in separate Catalyst 6500 series switches. If they are in the same chassis, you can create all of the VLANs on the same Catalyst 6500 series switch console.
Command

Purpose
Step 1
Switch-B(config)# vlan 
Enters the VLAN mode¹.
Step 2
Switch-B(vlan)# vlan 102
Creates VLAN 102².
Step 3
Switch-B(vlan)# vlan 104
Creates VLAN 104³.
Step 4
Switch-B(vlan)# vlan 200
Creates VLAN 200⁴.
¹Do this step on the switch console of the switch that contains CSM-S B.

²VLAN 102 provides a connection through Firewall 1 to CSM-S A.

³VLAN 104 provides a connection through Firewall 2 to CSM-S A.

⁴VLAN 200 provides the connection to the internal network.
Configuring VLANs on CSM-S B

To configure the three VLANs, perform this task:
Command

Purpose
Step 1
Switch-B(config)# module csm 6
Enters multiple module configuration mode and specifies that CSM-S B is installed in slot 6.
Step 2
Switch-B(config-module-csm)# vlan 102 
server
Specifies VLAN 102 as the VLAN that is being configured, identifies it as a server VLAN, and enters VLAN configuration mode.
Step 3
Switch-B(config-slb-vlan-server)# ip 
address 10.0.101.36 255.255.255.0
Specifies an IP address and netmask for VLAN 102.
Step 4
Switch-B(config-slb-vlan-server)# alias 
10.0.101.200 255.255.255.0
Specifies an alias IP address and netmask for VLAN 102¹.
Step 5
Switch-B(config-slb-vlan-server)# exit
Returns to multiple module configuration mode.
Step 6
Switch-B(config-module-csm)# vlan 104 
server
Specifies VLAN 104 as the VLAN that is being configured, identifies it as a server VLAN, and enters VLAN configuration mode.
Step 7
Switch-B(config-slb-vlan-server)# ip 
address 10.0.102.36 255.255.255.0
Specifies an IP address and netmask for VLAN 104.
Step 8
Switch-B(config-slb-vlan)# alias 
10.0.102.200 255.255.255.0
Specifies an alias IP address and netmask for VLAN 1041.
Step 9
Switch-B(config-slb-vlan-server)# exit
Returns to multiple module configuration mode.
Step 10
Switch-B(config-module-csm)# vlan 20 
server
Specifies VLAN 20 as the VLAN that is being configured, identifies it as a server VLAN, and enters VLAN configuration mode.
Step 11
Switch-B(config-slb-vlan-server)# ip 
address 10.1.0.36 255.255.255.0
Specifies an IP address and netmask for VLAN 20.
¹This step provides a target for CSM-S A to use in making a load-balancing decision.
Configuring Server Farms on CSM-S B

To configure three server farms on CSM-S B, perform this task:

Note SERVERS-SF specifies that client NAT will be performed using a pool of client NAT addresses that are created earlier in the example using the natpool command. You must create the NAT pool before referencing the command.
Command

Purpose
Step 1
Switch-B(config)# module csm 6
Enters multiple module configuration mode and specifies that CSM-S B is installed in slot 6.
Step 2
Switch-B(config-module-csm)# serverfarm 
FORWARD-SF
Creates and names the FORWARD-SF¹ server farm (actually a forwarding policy) and enters serverfarm configuration mode.
Step 3
Switch-B(config-slb-sfarm)# no nat server
Disables the NAT of server IP addresses and port numbers².
Step 4
Switch-B(config-slb-sfarm)# predictor 
forward
Forwards traffic in accordance with its internal routing tables rather than a load-balancing algorithm.
Step 5
Switch-B(config-slb-sfarm)# exit
Returns to multiple module configuration mode.
Step 6
Switch-B(config-module-csm)# serverfarm 
TO-OUTSIDE-SF
Creates and names the GENERIC-SF server farm and enters serverfarm configuration mode³.
Step 7
Switch-B(config-slb-sfarm)# no nat server
Disables NAT of server IP addresses and port numbers⁴.
Step 8
Switch-B(config-slb-sfarm)# real 
10.0.101.100
Identifies the alias IP address of CSM-S A that is locked on the path to Firewall 1 as a real server and enters real server configuration submode.
Step 9
Switch-B(config-slb-real)# inservice
Enables the real server (actually an alias IP address).
Step 10
Switch-B(config-slb-real)# exit
Returns to the serverfarm configuration mode.
Step 11
Switch-B(config-slb-sfarm)# real 
10.0.102.100
Identifies the alias IP address of CSM-S B that is located on the path to Firewall 2 as a real server and enters real server configuration submode.
Step 12
Switch-B(config-slb-real)# inservice
Enables the real server (actually an alias IP address).
Step 13
Switch-B(config-slb-real)# exit
Returns to serverfarm configuration mode.
Step 14
Switch-B(config-module-csm)# serverfarm 
SERVERS-SF
Creates and names the SERVERS-SF⁵ server farm and enters serverfarm configuration mode.
Step 15
Switch-B(config-slb-sfarm)# real 
10.1.0.101
Identifies a server in the intranet as a real server, assigns it an IP address, and enters real server configuration submode.
Step 16
Switch-B(config-slb-real)# inservice
Enables the real server.
Step 17
Switch-B(config-slb-real)# exit
Returns to serverfarm configuration mode.
Step 18
Switch-B(config-slb-sfarm)# real 
10.1.0.102
Identifies a server in the intranet as a real server, assigns it an IP address, and enters real server configuration submode.
Step 19
Switch-B(config-slb-real)# inservice
Enables the real server.
Step 20
Switch-B(config-slb-sfarm)# real 
10.1.0.103
Identifies a server in the intranet as a real server, assigns it an IP address, and enters real server configuration submode.
Step 21
Switch-B(config-slb-real)# inservice
Enables the real server.
¹FORWARD-SF is actually a route forwarding policy, not an actual server farm, that allows traffic to reach the intranet (through VLAN 20). It does not contain any real servers.

²This step is required when configuring a server farm that contains a forwarding policy rather than real servers.

³OUTSIDE-SF contains the two alias IP addresses of CSM-S A as the real servers allowing traffic from the intranet to reach CSM-S A.

⁴This step is required when configuring a server farm that contains a forwarding policy rather than real servers.

⁵SERVERS-SF contains the IP addresses of the real servers located within the intranet.
Configuring Virtual Servers on CSM-S B

To configure three virtual servers on CSM-S, perform this task:
Command

Purpose
Step 1
Switch-B(config)# module csm 6
Enters multiple module configuration mode and specifies that CSM-S B is installed in slot 6.
Step 2
Switch-B(config-module-csm)# vserver 
FORWARD-VS-102
Specifies FORWARD-VS as the virtual server that is being configured and enters virtual server configuration mode.
Step 3
Switch-B(config-slb-vserver)# virtual 
0.0.0.0 0.0.0.0 any
Specifies a match for any IP address and any protocol¹.
Step 4
Switch-B(config-slb-vserver)# vlan 102
Specifies that the virtual server will only accept traffic arriving on VLAN 102, which is traffic arriving from the secure side of the Firewall 1.
Step 5
Switch-B(config-slb-vserver)# serverfarm 
FORWARD-SF
Specifies the server farm for this virtual server².
Step 6
Switch-B(config-slb-vserver)# inservice
Enables the virtual server.
Step 7
Switch-B(config-slb-vserver)# exit
Returns to multiple module configuration mode.
Step 8
Switch-B(config-module-csm)# vserver 
FORWARD-VS-104
Specifies FORWARD-VS³ as the virtual server that is being configured and enters virtual server configuration mode.
Step 9
Switch-B(config-slb-vserver)# virtual 
0.0.0.0 0.0.0.0 any
Specifies a match for any IP address and any protocol1.
Step 10
Switch-B(config-slb-vserver)# vlan 104
Specifies that the virtual server will only accept traffic arriving on VLAN 104, which is traffic arriving from the secure side of the Firewall 2.
Step 11
Switch-B(config-slb-vserver)# serverfarm 
FORWARD-SF
Specifies the server farm for this virtual server2.
Step 12
Switch-B(config-slb-vserver)# inservice
Enables the virtual server.
Step 13
Switch-B(config-slb-vserver)# exit
Returns to multiple module configuration mode.
Step 14
Switch-B(config-module-csm)# vserver 
INSIDE-VS
Specifies INSIDE-VS⁴ as the virtual server that is being configured and enters virtual server configuration mode.
Step 15
Switch-B(config-slb-vserver)# virtual 
0.0.0.0 0.0.0.0 any
Specifies a match for any IP address and any protocol1.
Step 16
Switch-B(config-slb-vserver)# vlan 20
Specifies that the virtual server will only accept traffic arriving on VLAN 20, which is traffic arriving from the intranet.
Step 17
Switch-B(config-slb-vserver)# serverfarm 
TO-OUTSIDE-SF
Specifies the server farm for this virtual server (containing the alias IP addresses of CSM-S A as real servers and allowing traffic to flow through Firewalls 1 and 2) and enters real server configuration submode.
Step 18
Switch-B(config-slb-vserver)# inservice
Enables the virtual server.
Step 19
Switch-B(config-slb-vserver)# exit
Returns to multiple module configuration mode.
Step 20
Switch-B(config-module-csm)# vserver 
TELNET-VS
Specifies TELNET-VS⁵ as the virtual server that is being configured and enters virtual server configuration mode.

Note TELNET-VS does not use a VLAN limit; any source traffic (from firewalls or internal network) will be load balanced through this address.
Step 21
Switch-B(config-slb-vserver)# virtual 
10.1.0.200 255.255.255.0 tcp telnet
Specifies the IP address, netmask, protocol (TCP), and port (Telnet) for this virtual server⁶.
Step 22
Switch-B(config-slb-vserver)# serverfarm 
SERVERS-SF
Specifies the server farm containing real servers for this virtual server.
Step 23
Switch-B(config-slb-vserver)# inservice
Enables the virtual server.
¹Client matching is only limited by VLAN restrictions.

²This server farm is actually a forwarding predictor rather than an actual server farm containing real servers.

³FORWARD-VS allows traffic from the Internet to reach the intranet through VLAN 20.

⁴INSIDE-VS allows traffic from the intranet to reach CSM-S A through Firewall 1 (through VLANs 102 and 101) or
Firewall 2 (through VLANs 104 and 103).

⁵TELNET-VS allows traffic from the Internet to reach Telnet servers in the internal network.

⁶Clients reach the server farm represented by this virtual server through this address.
Configuring Regular Firewall Load Balancing

This section describes how to configure firewall load balancing for regular firewalls and provides the following information:

•Packet Flow in a Regular Firewall Configuration

•Regular Firewall Configuration Example

Packet Flow in a Regular Firewall Configuration

In a regular firewall configuration, firewalls connect to two different VLANs and are configured with IP addresses on the VLANs to which they connect. (See Figure 13-7.)

Figure 13-7 Regular Firewall Configuration Example

Item

Traffic Direction

Arrives On

Exits On

1

To intranet

VLAN 100

VLANs 101

2

To intranet

VLANs 201

VLAN 200 and 20

3

To Internet

VLAN 200 and 20

VLANs 201

4

To Internet

VLANs 101

VLAN 100

Figure 13-7 shows two regular firewalls (Firewall 1 and Firewall 2) located between two CSMs
(CSM-S A and CSM-S B). Traffic enters and exits the firewalls through shared VLANs (VLAN 101 and VLAN 201). Both regular firewalls have unique addresses on each shared VLAN.

VLANs provide connectivity to the Internet (VLAN 100), the internal network (VLAN 200), and to internal server farms (VLAN 20).

The CSM-S balances traffic among regular firewalls as if they were real servers. Regular firewalls are configured in server farms with IP addresses like real servers. The server farms to which regular firewalls belong are assigned a load-balancing predictor and are associated with virtual servers.

Regular Firewall Configuration Example

The regular firewall configuration example contains two CSM-S modules (CSM-S A and CSM-S B) installed in separate Catalyst 6500 series switches.

Note You can use this example when configuring two CSM-S modules in the same Catalyst 6500 series switch chassis. You can also use this example when configuring a single CSM-S in a single switch chassis, assuming that you specify the slot number of that CSM-S when configuring both CSM-S A and CSM-S B.

Configuring CSM-S A (Regular Firewall Example)

To create the regular configuration example, perform the following configuration tasks for CSM-S A:

•Creating VLANs on Switch A

•Configuring VLANs on CSM-S A

•Configuring Server Farms on CSM-S A

•Configuring Virtual Servers on CSM-S A

Note Although the configuration tasks are the same for both CSM-S A and CSM-S B, the steps, commands, and parameters that you enter are different.

Creating VLANs on Switch A

The example, shown in Figure 13-7, requires that you create two VLANs on Switch A.

Note This example assumes that the CSM-S modules are in separate Catalyst 6500 series switch chassis. If they are in the same chassis, all of the VLANs can be created on the same Catalyst 6500 series switch console.

To configure VLANs on Switch A, perform this task:
Command

Purpose
Step 1
Switch-A(config)# vlan 
Enters the VLAN mode¹.
Step 2
Switch-A(vlan)# vlan 100
Creates VLAN 100².
Step 3
Switch-A(vlan)# vlan 101
Creates VLAN 101³.
¹Do this step on the switch console of the switch that contains CSM-S A.

²VLAN 100 connects CSM-S A to the Internet.

³VLAN 101 connects CSM-S A to the insecure side of the firewalls.
Configuring VLANs on CSM-S A

To configure the two VLANs, perform this task:
Command

Purpose
Step 1
Switch-A(config)# module csm 5
Enters multiple module configuration mode and specifies that CSM-S A is installed in slot 5.
Step 2
Switch-A(config-module-csm)# vlan 100 
client
Specifies VLAN 100 as the VLAN that is being configured, identifies it as a client VLAN, and enters VLAN configuration mode.
Step 3
Switch-A(config-slb-vlan-client)# ip 
address 100.0.0.25 255.255.255.0
Specifies an IP address and netmask for VLAN 100.
Step 4
Switch-A(config-slb-vlan-client)# gateway 
100.0.0.13
Configures a gateway IP address for the router on the Internet side of CSM-S A.
Step 5
Switch-A(config-slb-vlan-client)# exit
Returns to multiple module configuration mode.
Step 6
Switch-A(config-module-csm)# vlan 101 
server
Specifies VLAN 101 as the VLAN that is being configured, identifies it as a server VLAN, and enters VLAN configuration mode.
Step 7
Switch-A(config-slb-vlan-server)# ip 
address 100.0.0.25 255.255.255.0
Specifies an IP address and netmask for VLAN 101.
Step 8
Switch-A(config-slb-vlan-server)# alias 
100.0.0.20 255.255.255.0
Specifies an alias IP address and netmask for VLAN 101¹.
¹This step provides a target for CSM-S B to use in making a load-balancing decision.
Configuring Server Farms on CSM-S A

Note Firewall 1 and Firewall 2 secure-side IP addresses are configured as real servers in the SEC-SF server farm associated with CSM-S B.

To configure two server farms on CSM-S A, perform this task:
Command

Purpose
Step 1
Switch-A(config)# module csm 5
Enters multiple module configuration mode and specifies that CSM-S A is installed in slot 5.
Step 2
Switch-A(config-module-csm)# serverfarm 
FORWARD-SF
Creates and names the FORWARD-SF¹ server farm (actually a forwarding policy) and enters serverfarm configuration mode.
Step 3
Switch-A(config-slb-sfarm)# no nat server
Disables the NAT of server IP addresses and port numbers².
Step 4
Switch-A(config-slb-sfarm)# predictor 
forward
Forwards traffic by adhering to its internal routing tables rather than a load-balancing algorithm.
Step 5
Switch-A(config-slb-sfarm)# exit
Returns to multiple module configuration mode.
Step 6
Switch-A(config-module-csm)# serverfarm 
INSEC-SF
Creates and names the INSEC-SF³ server farm (which will contain firewalls as real servers) and enters serverfarm configuration mode.
Step 7
Switch-A(config-slb-sfarm)# no nat server
Disables the NAT of the server IP address and port number⁴.
Step 8
Switch-A(config-slb-sfarm)# predictor 
hash address source 255.255.255.255
Selects a server using a hash value based on the source IP address⁵.
Step 9
Switch-A(config-slb-sfarm)# real 
100.0.0.3
Identifies Firewall 1 as a real server, assigns an IP address to its insecure side, and enters real server configuration submode.
Step 10
Switch-A(config-slb-real)# inservice
Enables the firewall.
Step 11
Switch-A(config-slb-real)# exit
Returns to serverfarm configuration mode.
Step 12
Switch-A(config-slb-sfarm)# real 
100.0.0.4
Identifies Firewall 2 as a real server, assigns an IP address to its insecure side, and enters real server configuration submode.
Step 13
Switch-A(config-slb-real)# inservice
Enables the firewall.
¹FORWARD-SF is actually a route forwarding policy, not an actual server farm, that allows traffic to reach the Internet (through VLAN 100); it does not contain any real servers.

²This is a required step when configuring a server farm that contains a forwarding policy rather than real servers.

³INSEC-SF contains (Firewall 1 and Firewall 2); their insecure-side IP addresses are configured as real servers in this server farm.

⁴This is a required step when configuring a server farm that contains firewalls.

⁵We recommend this step when configuring insecure-side firewall interfaces in a server farm.
Configuring Virtual Servers on CSM-S A

To configure two virtual servers on CSM-S A, perform this task:
Command

Purpose
Step 1
Switch-A(config)# module csm 5
Enters multiple module configuration mode and specifies that the CSM-S A is installed in slot 5.
Step 2
Switch-A(config-module-csm)# vserver 
FORWARD-VS
Specifies FORWARD-VS¹ as the virtual server that is being configured and enters virtual server configuration mode.
Step 3
Switch-A(config-slb-vserver)# virtual 
0.0.0.0 0.0.0.0 any
Specifies a match for any IP address and any protocol².
Step 4
Switch-A(config-slb-vserver))# vlan 101
Specifies that the virtual server will only accept traffic arriving on VLAN 101, which is traffic arriving from the insecure side of the firewalls.
Step 5
Switch-A(config-slb-vserver)# serverfarm 
FORWARD-SF
Specifies the server farm for this virtual server³.
Step 6
Switch-A(config-slb-vserver)# inservice
Enables the virtual server.
Step 7
Switch-A(config-slb-vserver)# exit
Returns to multiple module configuration mode.
Step 8
Switch-A(config-module-csm)# vserver 
INSEC-VS
Specifies INSEC-VS⁴ as the virtual server that is being configured and enters virtual server configuration mode.
Step 9
Switch-A(config-slb-vserver)# virtual 
200.0.0.0 255.255.255.0 any
Specifies the IP address, netmask, and protocol (any) for this virtual server⁵.
Step 10
Switch-A(config-slb-vserver))# vlan 100
Specifies that the virtual server will only accept traffic arriving on VLAN 100, which is traffic arriving from the Internet.
Step 11
Switch-A(config-slb-vserver)# serverfarm 
INSEC-SF
Specifies the server farm for this virtual server⁶.
Step 12
Switch-A(config-slb-vserver)# inservice
Enables the virtual server.
¹FORWARD-VS allows Internet traffic to reach the insecure side of the firewalls (through VLAN 101).