SSL Termination on the Cisco Application Control Engine Using an Existing Chained Certificate and Key in One Arm Mode Configuration Example
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Revision as of 18:37, 4 December 2008
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. It will also assume that the certificate requires an intermediate certificate to be supplied to the client browser as well. Typically this happens when a CA signs the issued server certificate with an intermediate certificate not yet integrated into Internet Explorer, Firefox, and other browsers. When this occurs, the browser must supply both the server certificate and the updated intermediate certificate to prevent any security errors from being shown to the user.
|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 One Arm Mode with Source NAT on the Cisco Application Control Engine Configuration Example.|
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). ACE will rewrite the destination IP to that of the rserver, and rewrite the source IP with one from a nat-pool. Once the client request is fully NAT’d it will be sent to the server over the same VLAN which it was originally received. The server will respond to the ACE, based on the source IP of the request. The ACE will receive the response, change the source IP to be the VIP, and send it to the MSFC. The MSFC will forward the response to the client. The following figure illustrates this process.
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. This document assumes that the reader has already acquired these items using one of the two methods mentioned.
|Note:||If you have not yet obtained a certificate and key, the SSL Termination on the Cisco Application Control Engine Without an Existing Chained Certificate and Key in One Arm Mode Configuration Example 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/onearm(config)# class-map match-all 102-vip ACE-1/onearm(config-cmap)# match virtual-address 172.16.5.102 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/onearm# 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/onearm# crypto import ftp 172.25.91.127 cisco cert.pem cert.pem ACE-1/onearm# 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/onearm# 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/onearm# 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/onearm(config)# ssl-proxy service proxy-1 ACE-1/onearm(config-ssl-proxy)# cert cert.pem ACE-1/onearm(config-ssl-proxy)# key key.pem
In addition to applying a certificate and key to the proxy service, configure a chaingroup to supply the intermediate certificate to the client’s browser.
ACE-1/ACE-1/onearm(config)# crypto chaingroup intermed-1 ACE-1/ACE-1/onearm(config-chaingroup)# cert intermediate.pem
The chaingroup needs to be applied to the ssl-proxy service in addition to the already configured certificate and key.
ACE-1/ACE-1/onearm(config)# ssl-proxy service proxy-1 ACE-1/ACE-1/onearm(config-ssl-proxy)# chaingroup intermed-1
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/onearm(config)# policy-map multi-match client-vips ACE-1/onearm(config-pmap)# class 102-vip ACE-1/onearm(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/onearm# show crypto files ACE-1/onearm# show crypto certificate all ACE-1/onearm# show crypto key all ACE-1/onearm# show crypto session ACE-1/onearm# show crypto hardware ACE-1/onearm# show service-policy <name> detail
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:
logging enable crypto chaingroup intermed-1 cert intermediate.cert 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 192.168.5.11 inservice rserver host lnx2 ip address 192.168.5.12 inservice rserver host lnx3 ip address 192.168.5.13 inservice rserver host lnx4 ip address 192.168.5.14 inservice rserver host lnx5 ip address 192.168.5.15 inservice ssl-proxy service proxy-1 key key.pem cert cert.pem chaingroup intermed-1 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 172.16.5.102 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 nat dynamic 5 vlan 50 interface vlan 50 description "Client-Server VLAN" ip address 172.16.5.5 255.255.255.0 access-group input everyone service-policy input client-vips service-policy input remote-access nat-pool 5 172.16.5.200 172.16.5.209 netmask 255.255.255.0 pat no shutdown ip route 0.0.0.0 0.0.0.0 172.16.5.1