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Scaling Your Cisco IronPort Web Security Appliance Using Cisco Application Control Engine

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Executive Summary

This guide discusses a validated scalable deployment option for the Cisco IronPort™ Web Security Appliance (Cisco IronPort WSA) S-Series as a transparent proxy using the Cisco ® Application Control Engine (ACE).
Because of its proxy architecture, Cisco IronPort Cisco IronPort WSA is commonly deployed using transparent redirection through the Web Cache Control Protocol (WCCP). Although WCCP is a very capable interception engine, the combination of Cisco IronPort Cisco IronPort WSA and Cisco ACE creates a solution architecture that provides a more robust, scalable, and flexible solution than is possible using WCCP. In certain network environments, WCCP is not feasible and is incompatible with preexisting features such as Virtual Routing and Forwarding (VRF), Cisco IOS ® Software version requirements, and complex configurations, and Cisco IOS Software products and third-party products offer varying degrees of WCCP support. Cisco ACE provides an alternative means of transparently intercepting outgoing web traffic and intelligently directing it to a group of Cisco IronPort Cisco IronPort WSA devices. This approach mitigates the dependencies of the WCCP solution and significantly increases scalability, extending the number of Cisco IronPort Cisco IronPort WSA devices beyond the 32-device limit of WCCP. The virtualization capabilities of the Cisco ACE allow it to be securely used as a server load balancer as well, combining multiple application functions in a single platform.


Cisco ACE can transparently redirect Internet traffic to a cluster of Cisco IronPort WSA proxy servers. The transparent proxy solution allows network administrators to quickly deploy proxies anywhere in the network with no modification to end-user browsers or other software. The Cisco IronPort WSA S-Series provides a scalable proxy platform architecture to protect and accelerate the delivery of business applications.
Cisco ACE offers enterprises and service providers a highly resilient server load-balancing solution. Cisco ACE is available in two form factors: a standalone appliance and a module for Cisco Catalyst ® 6500 Series Switches and Cisco 7600 Series Routers. The Cisco ACE transparent mode capability offers client protection, improves Internet response time, and reduces WAN operating costs by redirecting web traffic destined for remote Internet sites to a group of local proxy cache servers.
The Cisco IronPort WSA S-Series delivers a scalable proxy platform architecture to protect web traffic and accelerate the delivery of business applications. Figure 1 shows the main components of the Cisco IronPort WSA S-Series solution.

Figure 1. Main Components of Cisco IronPort WSA S-Series


Proxy technology inherently relies on interception technologies to deliver traffic to the proxy server group for protection and acceleration. These methods include explicit proxy (inline), proxy automatic configuration (PAC) file distribution (through direct upload, Dynamic Host Configuration Protocol [DHCP], or Domain Name System [DNS]), WCCP, and Cisco ACE technology. Explicit proxy requires massive resources to manually configure every client system. PAC files also present deployment challenges. WCCP, which provides Layer 2 transparent cache switching, has been the most commonly used redirection mechanism in the data center to date. However, the Cisco ACE, which provides a Layer 7 intelligent Layer 2-style transparent cache switching service, can be deployed as a Layer 2 redirection engine offering many benefits over the traditional WCCP engine, including scalability (16-Gbps throughput and 4 million connections), high availability and robustness (uninterrupted Internet access in high-availability mode) Layer 7 awareness, and advanced monitoring of Cisco IronPort WSA services.
In a traditional proxy deployment, the client's IP address is replaced with that of the proxy or cache server. Although this approach provides inherent security by masking the address of the end user, in some cases certain web applications require access to the originating client's IP address.
In many cases in which the client IP address must be preserved when it reaches the originating server, the Cisco ACE can easily be deployed because its default behavior is to preserve client IP addresses. In addition, the Cisco ACE supports 5-tuple flow matching and source MAC address matching to help ensure proper flow paths through the design. The Cisco ACE feature known as MAC-sticky helps ensure that the response traffic is given to the device that originated the connection, instead of the traffic's being routed as would happen in traditional proxy environments. To help ensure that only traffic destined for Cisco IronPort WSA is sent through the Cisco ACE and Cisco IronPort WSA solution, the router (a Cisco Catalyst 6500 Series Multilayer Switch Feature Card [MSFC] in this case) uses policy-based routing to force traffic to the Cisco ACE to be processed and forwarded to the Cisco IronPort WSAs.
In many cases, the Cisco IronPort WSA performs better when traffic is sent to it based on Layer 7 information. This approach is problematic for traditional proxy solutions such as WCCP, in which flow decisions are made at the connection level. The Cisco ACE offers a rich set of Layer 7 classifications that allow it to easily make per-request decisions to distribute traffic optimally to each Cisco IronPort WSA device.

Cisco ACE Solution

Cisco ACE supports load balancing of transparent and conventional proxy servers. Cisco ACE provides several load-balancing methods, which you can apply depending on how you want to distribute data over the proxy farm (for example, using the entire URL, a URL string, the entire domain name, or a domain string).
Cisco ACE can look at the URL requested by the client and determine the most appropriate proxy server to send it to based on the URL request, proxy server load, and availability. Cisco IronPort WSA supports request-based caching (passive caching) that is HTTP compliant. Requests are filled from the cache when a fresh (not stale) copy is available (cache hit). Cisco IronPort WSA does not support active caching or proactive refreshing of its cache; hence, dynamic pages (for example, URLs with cookies and Common Gateway Interface [CGI]) are fetched directly by the proxy on a per-request basis.
Health checks (probes) can easily be added to the Cisco ACE to help ensure the quality of the service. Cisco ACE will take a proxy server out of rotation when a failure is detected. If all proxy servers become unavailable, Cisco ACE allows all client requests to bypass them and sends the requests directly the originating servers (fail open).

Traffic Flow

Figure 2 shows the traffic flows for this solution.

Figure 2. Traffic Flow

The traffic flow is as follows:
1. The Cisco Catalyst 6500 Series MSFC uses policy-based routing (PBR) on interface Vlan550 to route web traffic destined to TCP port 80 to the Cisco ACE.
2. Cisco ACE transparently load balances the traffic with the Cisco IronPort WSA farm by performing a Layer 2 MAC address rewrite, preserving the source and destination IP addresses of the connection. Cisco IronPort WSA validates the request with its configured security policies and delivers the requested content if a cached version is available (cache hit).
3. If Cisco IronPort WSA does not have the requested content or if the HTTP request includes the no-cache control option, Cisco IronPort WSA sends a request to the web server. Cisco IronPort WSA initiates a connection to the web server with the client IP address as the source address, with IP spoofing enabled. The Cisco Catalyst 6500 Series MSFC uses PBR on Vlan551 to forward return traffic (TCP traffic with source port 80) back to the requesting Cisco IronPort WSA.

Cisco ACE Design

Following are the best practices for configuring Cisco ACE for transparent caching:

• Virtual IP address: The virtual IP address typically is a catch-all address for a specific Layer 4 port.

• Predictor algorithm: To optimize caching, the typical predictor that can be used is predictor hash url. All other Cisco ACE predictors, such as predictor hash header and predictor hash destination, can also be used.

• Load-balancing policy: A Layer 4 class map is configured so that all requests will be load-balanced across Cisco IronPort WSA devices.

• MAC-sticky: Since the proxy servers have IP spoofing enabled, the TCP connections to the Internet that originate from the proxy servers will have the client IP address as the source. MAC-sticky is used on the interface connecting the Cisco IronPort WSA farm, and it enables Cisco ACE to route flow-based traffic by MAC address, bypassing a routing table decision. This approach is used to help ensure proper connection persistence for Cisco ACE.

• Probes: To verify the correct functioning of the Cisco IronPort WSA devices, you should enable HTTP probes. HTTP probes can be configured to request a page from one or more common internet websites. Note that if you send probes to multiple websites, you should add the "fail-on-all" option to the configuration section with the probe statements.

• Backup server farm: To help ensure uninterrupted service when all the Cisco IronPort WSA devices in the Cisco IronPort WSA server farm are down, you should configure a backup server farm that transparently forwards traffic to the Cisco Catalyst 6500 Series MSFC on Vlan540.

Cisco ACE, Cisco IronPort WSA, and Cisco Catalyst 6500 Series Switch Configuration

Cisco ACE supports up to 250 virtual contexts. When deploying Cisco ACE, the recommended practice is to use the Admin context to facilitate overall management of the Cisco ACE device and to create a designated context for each specific application for load balancing. In this solution, a context named "Cisco IronPort WSA" is created for the transparent proxy.

Admin Context Configuration

The Admin context configuration is shown here:
Generating configuration....
boot system image:c4710ace-mz.A3_2_5.bin
login timeout 0
hostname sandbox-pod3-aceapp2
clock timezone standard PST
clock summer-time standard PDT
ntp server
ip domain-name
ip name-server
ip name-server
policy-map type management first-match mgmt
class remote-access
interface vlan 110
ip address
service-policy input mgmt
no shutdown
ip route
context ironport-Cisco IronPort WSA
allocate-interface vlan 643-644

Cisco IronPort WSA Context Configuration

The Cisco IronPort WSA context configuration is shown here:
generating configuration....
access-list everyone line 10 extended permit ip any any
probe icmp PING
ip address
probe http CISCO
ip address
interval 10
faildetect 5
passdetect interval 30
request method head url /index.html
expect status 200 200
probe http YAHOO
ip address
interval 10
faildetect 5
passdetect interval 30
request method head url /index.html
expect status 200 200
rserver host MSFC
ip address
rserver host Cisco IronPort WSA-01
ip address
rserver host Cisco IronPort WSA-02
ip address
serverfarm host ROUTE
probe PING
rserver MSFC
serverfarm host Cisco IronPort WSAFARM
predictor hash url
probe CISCO
probe YAHOO
rserver Cisco IronPort WSA-01 80
rserver Cisco IronPort WSA-02 80
class-map match-all WEB-TRAFFIC
2 match virtual-address tcp eq www
policy-map type loadbalance first-match Cisco IronPort WSA-LB
class class-default
serverfarm Cisco IronPort WSAFARM backup ROUTE
policy-map multi-match LB
loadbalance vip inservice
loadbalance policy Cisco IronPort WSA-LB
loadbalance vip icmp-reply active
interface vlan 643
description To MSFC
ip address
access-group input everyone
service-policy input LB
no shutdown
interface vlan 644
description To Cisco IronPort WSA Proxy Interface (P1)
ip address
mac-sticky enable
access-group input everyone
no shutdown
ip route

Cisco Catalyst 6500 Series Configuration

The Cisco Catalyst 6500 Series configuration is shown here:
svclc multiple-vlan-interfaces
svclc module 3 vlan-group 1
svclc vlan-group 1 643,644
interface Vlan641
description Cisco IronPort WSA-ClientUsers
ip address
ip policy route-map CLIENT-TCP80
interface Vlan642
ip address
ip policy route-map SERVER-TCP80
interface Vlan643
description Cisco IronPort WSA-ACE_MSFC
ip address
access-list 109 permit tcp any any eq www
access-list 110 permit tcp any eq www any
route-map SERVER-TCP80 permit 10
match ip address 110
set ip next-hop
route-map CLIENT-TCP80 permit 10
match ip address 109
set ip next-hop
! static routes to internet addresses hosted on a demo server
ip route
ip route
ip route

Cisco IronPort WSA Configuration

The Cisco IronPort WSA configuration is show here:
1. In the initial System Setup wizard, select Transparent mode deployment. Transparent mode supports both explicit forward mode and WCCPv2 and Layer 4 switch environments.

Description: Picture 1

Both management port M1 and web proxy data port P1 are set up
Cisco IronPort WSA-1:
Cisco IronPort WSA-2:

2. Make sure Layer 4 Switch is selected.
Description: Picture 3
3. Enable IP Spoofing globally.

Description: Picture 2


The robust Cisco ACE and Cisco IronPort WSA transparent proxy solution offers several configurable options that can be tuned according to the requirements. In addition, performance and throughput capabilities make this a highly scalable solution. Cisco ACE provides a high level of scalability, and with stateful redundancy and the capability to intelligently distribute traffic across Cisco IronPort WSA on a per-request basis, it provides an excellent solution.

For More Information

• For more information about Cisco ACE, visit

• For more information about Cisco IronPort WSA, visit

• For more information about Cisco Application Networking Services (ANS), Cisco data center solutions for Cisco ANS, and Cisco ACE, visit or contact your local Cisco account representative.