SSL Termination on the Cisco Application Control Engine Using an Existing Certificate and Key in Bridged Mode Configuration Example
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Contents |
Goal
This document describes how to configure Secure Sockets Layer (SSL) termination on the Cisco® Application Control Engine (ACE) for an existing basic load-balancing configuration. This type of configuration will remove the burden of SSL encryption/decryption from the real servers’ CPUs, increasing the amount of traffic they are able to handle in most situations. This document assumes that the reader already has generated or purchased a certificate and its associated RSA key.
 | Note: | This document does not cover the design and configuration of the basic load-balancing configuration; this is covered in the Basic Load Balancing Using Bridged Mode on the Cisco Application Control Engine Configuration Example. |
Design
Clients will establish a connection using HTTPS (SSL) to the virtual IP address (VIP) configured on the Cisco ACE. HTTPS causes the client’s TCP session to be encrypted between the browser and the ACE. Once the session reaches the ACE, the ACE will decrypt the session and forward it to a real server in clear text (HTTP). The VIP used in this example resides in an ACE context which is configured with a client VLAN, a server VLAN, and a BVI to tie the VLANs together in a bridge-group. The following figure illustrates this process.
Configuration
In order for the Cisco ACE to be able to terminate SSL sessions, it will need to be configured with both an SSL certificate and a corresponding SSL key. Once imported, these SSL files are associated with an SSL proxy service that is applied to the VIP to enable SSL termination.
SSL files (both certificate and key) can either be generated using a tool such as OpenSSL or requested from a certificate authority such as Verisign or GoDaddy. The next sections will cover both of these methods.
| Note: | If you have not yet obtained a certificate and key, the Configuring SSL Termination on ACE Without an Existing Certificate and Key in Bridged Mode ACE Example Series document provides a tutorial on how to request one from a certificate authority, as well as how to generate one using OpenSSL. |
The SSL termination configuration begins like the basic Layer 4 load-balancing configuration, by defining a VIP and corresponding server farm and rservers. Although the VIP can be configured with a port of “any,” the ACE will do a TCP reset on any non-SSL connections. To prevent this, it is recommended that you bind the VIP to a port. In this example, the IP address 172.16.1.100 and port 443 will be used.
ACE-1/bridged(config)# class-map match-all 102-vip ACE-1/bridged(config-cmap)# match virtual-address 172.16.3.102 tcp eq 443
When adding the rservers to the server farm, consider the destination of the decrypted traffic. In almost every case, encrypted SSL traffic is received on an SSL-specific port, and the decrypted traffic needs to be sent to another port on the real servers. The Cisco ACE uses the rserver port defined in the server farm to properly translate (using Port Address Translation [PAT]) the destination for the decrypted connection.
ACE-1/bridged# show run serverfarm
Generating configuration....
serverfarm host web
rserver lnx1 80
inservice
rserver lnx2 80
inservice
rserver lnx3 80
inservice
rserver lnx4 80
inservice
rserver lnx5 80
inservice
The VIP and server farm in this example allow the Cisco ACE to accept connections to the VIP on port 443 and forward them to a real server on port 80. Note that if the port is not provided, the VIP port will be preserved.
Most SSL termination configurations begin by importing the certificate and key onto the Cisco ACE. The easiest way to accomplish this is by placing the two files onto a secure FTP (SFTP) or FTP server so they can be transferred to the ACE.
ACE-1/bridged# crypto import ftp 172.25.91.127 cisco cert.pem cert.pem ACE-1/bridged# crypto import ftp 172.25.91.127 cisco key.pem key.pem
| Note: | If the files are in privacy enhanced mail (PEM) format, you can cut and paste to import the SSL file using the terminal parameter. For information on how to use the “crypto import” command, visit the following URL: http://cisco.com/en/US/docs/interfaces_modules/services_modules/ace/v3.00_A2/command/reference/execmds.html#wp1616651 |
Once the SSL files have been imported, they should be checked to ensure that they were uploaded properly and to verify that they match. If the two files do not match, the RSA key cannot be exchanged and the ACE will not be able to properly terminate client connections.
ACE-1/bridged# show crypto files
Filename File File Expor Key/
Size Type table Cert
-----------------------------------------------------------------------
cert.pem 1354 PEM Yes CERT
key.pem 887 PEM Yes KEY
ACE-1/bridged# crypto verify key.pem cert.pem
Keypair in key.pem matches certificate in cert.pem.
After the SSL files have been verified, the Cisco ACE can be configured with an SSL proxy service, which is a logical grouping of the certificates, key, and SSL parameters used to define the characteristics of SSL termination on the ACE.
ACE-1/bridged(config)# ssl-proxy service proxy-1 ACE-1/bridged(config-ssl-proxy)# cert cert.pem ACE-1/bridged(config-ssl-proxy)# key key.pem
Within the ACE, all SSL termination is fully integrated. Therefore, there is no need to configure internal VLANs or IPs to handle decrypted traffic. All that is required to enable SSL termination is to attach the SSL proxy service configured above to a VIP in a service policy.
ACE-1/bridged(config)# policy-map multi-match client-vips ACE-1/bridged(config-pmap)# class 102-vip ACE-1/bridged(config-pmap-c)# ssl-proxy server proxy-1
At this point the ACE should be configured with a working SSL termination configuration. Make a test connection to the VIP address using HTTPS in a web browser, and you should see a response from one of the real servers.
Related show Commands
This section provides information you can use to confirm your configuration is working properly.
Certain show commands are supported by the Output Interpreter Tool (registered customers only), which allows you to view an analysis of show command output.
ACE-1/bridged# show crypto files ACE-1/bridged# show crypto certificate all ACE-1/bridged# show crypto key all ACE-1/bridged# show crypto session ACE-1/bridged# show crypto hardware ACE-1/bridged# show service-policy <name> detail
Comments
Once the configuration is complete, check to make sure the VIP address can be accessed via HTTPS in a web browser. If any certificate errors are shown, this indicates a problem with the certificate, not with the Cisco ACE configuration. The above commands can be used to verify that SSL sessions are being terminated successfully.
When a client’s web browser connects to an SSL server on any device, the browser and server negotiate which encryption cipher to use for the session. The list and order of ciphers presented by the ACE in a default configuration are as follows.
1. CM_SSL_RSA_WITH_RC4_128_MD5 2. CM_SSL_RSA_WITH_RC4_128_SHA 3. CM_SSL_RSA_WITH_DES_CBC_SHA 4. CM_SSL_RSA_WITH_3DES_EDE_CBC_SHA 5. CM_SSL_RSA_WITH_AES_128_CBC_SHA 6. CM_SSL_RSA_WITH_AES_256_CBC_SHA 7. CM_SSL_RSA_EXPORT_WITH_RC4_40_MD5 8. CM_SSL_RSA_EXPORT1024_WITH_RC4_56_MD5 9. CM_SSL_RSA_EXPORT_WITH_DES40_CBC_SHA 10. CM_SSL_RSA_EXPORT1024_WITH_DES_CBC_SHA 11. CM_SSL_RSA_EXPORT1024_WITH_RC4_56_SHA
If this list is not desirable or the order needs to be changed, an SSL parameter map can be configured to make such changes. The documentation on this feature can be found at the following URL:
show running-config
logging enable
access-list everyone line 8 extended permit ip any any
access-list everyone line 16 extended permit icmp any any
rserver host lnx1
ip address 192.168.3.11
inservice
rserver host lnx2
ip address 192.168.3.12
inservice
rserver host lnx3
ip address 192.168.3.13
inservice
rserver host lnx4
ip address 192.168.3.14
inservice
rserver host lnx5
ip address 192.168.3.15
inservice
ssl-proxy service proxy-1
key key.pem
cert cert.pem
serverfarm host web
rserver lnx1 80
inservice
rserver lnx2 80
inservice
rserver lnx3 80
inservice
rserver lnx4 80
inservice
rserver lnx5 80
inservice
class-map match-all 102-vip
2 match virtual-address 172.16.3.102 tcp eq https
policy-map type management first-match remote-access
class class-default
permit
policy-map type loadbalance http first-match slb
class class-default
serverfarm web
policy-map multi-match client-vips
class 102-vip
loadbalance vip inservice
loadbalance policy slb
ssl-proxy server proxy-1
interface vlan 30
description "Client Side"
bridge-group 3
access-group input everyone
service-policy input client-vips
no shutdown
interface vlan 31
description "Server Side"
bridge-group 3
service-policy input remote-access
no shutdown
interface bvi 3
ip address 172.16.3.5 255.255.255.0
description "client - server bridge group"
no shutdown
ip route 0.0.0.0 0.0.0.0 172.16.3.1
