Cisco DistributedDirector 2500 Series Install and Config Guide
Configuring HTTP Session Redirector Mode
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Configuring HTTP Session Redirector Mode

Table Of Contents

Configuring HTTP Session Redirector Mode

Planning the Installation

Configuration Tasks

Configure the Director

Specify the IP Address on Which the Director Receives HTTP Requests

Specify the DNS Server to Which the Director Sends Requests

Configure the Default Weight Metrics

Define an Access List to Enable Security for DRP

Configure a Regular Expression for Address Sorting

Set Up MD5 Authentication With Passwords as Another Security Measure

Configure DRP-Associations, Host-Specific Weights, Priorities, and Preferences on the Director

Identify the Subdomain Name and IP Addresses of the Distributed Servers

Associate Each Distributed Server With its DRP Server Agent

Specify Information for Server Verification

Specify Host-Specific Weights or Metric Priorities

Set Up Server Preferences

Configure the Primary DNS Server

Test the Configuration

Sample Configuration

How the Configuration Works

Sample Director Configuration

Sample DRP-Associations, Host-Specific Weights, Priorities, and Preferences on the Director

Sample Primary DNS Server


Configuring HTTP Session Redirector Mode


This chapter describes how to configure the Cisco DistributedDirector (the Director) and the primary domain DNS server for HTTP session redirector mode.

To configure the Director for HTTP session redirector mode, you need to set up the software on the following network equipment:

Cisco DistributedDirector 2500 Series

Primary domain DNS server

Cisco routers with DRP server agent enabled


Note   The primary DNS server and the Director are configured differently for DNS caching name server and HTTP session redirector modes. The DRP server agents are enabled in the same manner for either mode. Configuring DRP server agents is described in the chapter "."


DNS caching name server mode works for all IP services. HTTP session redirector mode works only for HTTP services. You should choose the mode that best meets your networking requirements for a particular group of distributed servers. The Director supports multiple groups of distributed servers, and each group can operate in different configurations and modes.

HTTP session redirector mode configuration is described in the following sections:

Planning the Installation

Configuration Tasks

Sample Configuration

For more complete information about Director commands, see the chapter "."

Planning the Installation

You need to gather or assign the following:

DNS name and IP address for the Director.

One or more virtual IP addresses. The IP address must be a valid address for the subnet to which the Director is connected. (A good choice is the next host number after the Director interface address.)

Name and IP address of the primary DNS server for the domain above the Director subdomain, as well as secondary DNS servers for the domain. (For example, sleet.com could be the domain and www.sleet.com could be the subdomain.)

For each distributed server site, the IP address and DNS name of a Cisco router, with Cisco IOS Release 11.2(4)F or later, configured as a DRP server agent. DRP server agents are required only when you need to use DRP metrics.

Key chain password (a character string without spaces) that you will use for Message Digest algorithm 5 (MD5) authentication between the Director and the DRP server agents. An MD5 password is required only when the DRP server agent uses MD5 authentication.

The Director can be placed anywhere in the corporate intranet. For ease of management, you should install the Director topologically close to the primary DNS server.

Configuration Tasks

The following sections describe how to configure the Director and the DNS server for HTTP session redirector mode:

Configure the Director

Configure DRP-Associations, Host-Specific Weights, Priorities, and Preferences on the Director

Configure the Primary DNS Server

Test the Configuration

For information on advanced configuration options, refer to the chapter "."

Configure the Director

Perform the following steps to configure the Director for HTTP session redirector mode. Tasks associated with each step are provided in the subsections that follow:


Step 1 Specify the IP Address on Which the Director Receives HTTP Requests

Step 2 Specify the DNS Server to Which the Director Sends Requests

Step 3 Configure the Default Weight Metrics

Step 4 Define an Access List to Enable Security for DRP

Step 5 Configure a Regular Expression for Address Sorting

Step 6 Set Up MD5 Authentication With Passwords as Another Security Measure

Specify the IP Address on Which the Director Receives HTTP Requests

Perform the following steps in global configuration mode to specify the IP address on which the Director will receive HTTP requests:

Task
Command

Step 1 Configure the Ethernet interface.

Refer to the chapter "."

Step 2 Specify the IP address on which the Director will receive HTTP requests.

ip director ip-address Director-virtual-IP-address


For example:

ip director ip-address 10.0.0.4

You can specify multiple IP addresses with separate commands. The IP address must be a valid address for the subnet to which the Director is connected. (A good choice is the next host number after the Director interface address.)

Specify the DNS Server to Which the Director Sends Requests

Perform the following task in interface configuration mode:

Task
Command

Specify the DNS server to which the Director should send requests.

ip name-server DNS-server-IP-address


This is the Director's default DNS server (the primary domain's DNS primary server).

Configure the Default Weight Metrics

To configure default weight metrics, perform the following task in global configuration mode:

Task
Command

Configure the default weight metrics.

ip director default-weights {[drp-int n] [drp-ext n] [drp-ser n] [random n] [admin n]}


Default weights are used for all host names sorted by the Director. Following are the valid metric options:

Random metric (random)

DRP-external metric (drp-ext)

DRP-internal metric (drp-int)

DRP-server metric (drp-ser)

Administrative metric (admin)

When the associated metric is referenced in the sorting decision, it is always multiplied by the appropriate metric weight. In this way, you can specify that some metrics weigh more heavily than others. You may determine the weights you want to use through experimentation. The weights do not need to add to 100.

To override default weights for a certain host, specify host-specific weights in the Director configuration. For more information, also refer to the section "Setting Metrics and the Server Connection Parameter" in the chapter "."

To view the default weights setting, use the show ip director default-weights command.

Define an Access List to Enable Security for DRP

Perform the following tasks in global configuration mode to define an access list to enable security for DRP:

Task
Command

Step 1 Define an access list that permits replies from each of the DRP server agents. Specify the DRP-agent IP address as the source.

access-list access-list-number permit [source]

Step 2 Deny all other requests.

access-list access-list-number deny any

Step 3 Enable the access list.

ip drp access-group access-list-number


In the following example, replies from DRP server agents with IP addresses 10.0.0.2, 11.0.0.2, and 12.0.0.2 are allowed:

access-list 1 permit 10.0.0.2
access-list 1 permit 11.0.0.2
access-list 1 permit 12.0.0.2
access-list 1 deny any

ip drp access-group 1

Configure a Regular Expression for Address Sorting

Perform the following tasks in global configuration mode to configure a regular expression which the Director uses to match against host names. If the host name in the incoming DNS A (address) query matches the pattern specified in the Director access list, then the Director will be asked to sort the addresses. If not, all addresses will be returned in the response as normal.

Task
Command

Step 1 Specify the host names that the Director should sort.

ip director access-list access-list-number [permit | deny] expression

Step 2 Tell the Director to use the access list.

ip director access-group access-list-number


For example:

ip director access-list 1 permit "^www." 
ip director access-list 1 deny any

ip director access-group 1

If ip director access-group is not configured, then all host names are considered "interesting" to the Director. All incoming DNS A queries will then be passed to the Director for address sorting before the creation of the A response.

Set Up MD5 Authentication With Passwords as Another Security Measure

Perform the following tasks in global configuration mode to set up MD5 authentication with passwords:

Task
Command

Step 1 Set up a key chain and password.

key chain name-of-chain

key number

key-string text

Step 2 Enable the DRP authentication key chain.

ip drp authentication key-chain name-of-chain


The key chain is an encrypted password that helps prevent DRP-based denial-of-service attacks, which can be a security threat. The key chain (a character string without spaces) must match the key chain of the DRP server agents to which the Director communicates.

Configure DRP-Associations, Host-Specific Weights, Priorities, and Preferences on the Director

The tasks associated with these steps are described in the subsections that follow:


Step 1 Identify the Subdomain Name and IP Addresses of the Distributed Servers

Step 2 Associate Each Distributed Server With its DRP Server Agent (if you intend to configure DRP metrics)

Step 3 Specify Information for Server Verification

Step 4 Specify Host-Specific Weights or Metric Priorities

Step 5 Set Up Server Preferences

Identify the Subdomain Name and IP Addresses of the Distributed Servers

Perform the following task in global configuration mode:

Task
Command

Identify the subdomain name and IP addresses of the distributed servers.

ip host name address1 [ddress2...address8]


For example, you might use the following command:

ip host www-servers.sleet.com 10.0.0.2 11.0.0.2 12.0.0.2

This identifies the distributed servers with IP addresses 10.0.0.2, 11.0.0.2, and 12.0.0.2, as members of the www-servers.sleet.com domain.

Associate Each Distributed Server With its DRP Server Agent

If you intend to configure any DRP metrics, associate each distributed server with its DRP server agent.

Perform the following task in global configuration mode:

Task
Command

Associate each distributed server with its DRP server agent.

ip director server {hostname | host-ip-address} drp-association {name | ip-address}


The following example associates the distributed server with the IP address 11.0.0.2 with the DRP server agent at IP address 11.0.0.3:

ip director server 11.0.0.2 drp-association 11.0.0.3

or

ip director server www-west.sleet.com. drp-association 
drp-west.sleet.com.

The Director will query its default DNS server for name-to-address bindings. If you use host/router names instead of IP addresses, make sure you configure the appropriate A records in the Director's default DNS server. You should use your primary domain server as the Director's default DNS server to ensure that all such name-to-address binding requests can be satisfied.

Specify Information for Server Verification

Perform the following task in global configuration mode:

Task
Command

Specify information for server verification.

ip director host name connect port connection-interval


For example, you would use the following command to instruct the Director to create a TCP connection to port 80 on each distributed server associated with www.sleet.com every 15 minutes:

ip director host www-servers.sleet.com connect 80 15

Servers that yield unsuccessful TCP connections are marked as unavailable. Subsequent successful TCP connections to the server will reinstate it as available. See "Specifying the Server Connection Parameter" in the chapter "Configuring Advanced Features" for more details.

Specify Host-Specific Weights or Metric Priorities

To specify host-specific weights or metric priorities, perform either or both of the following tasks in global configuration mode:

Task
Command

Specify host-specific weights.

ip director host name weights {[drp-int n] [drp-ext n] [drp-ser n] [random n] [admin n]}

Specify metric priorities.

ip director host name priority {[drp-int n] [drp-ext n] [drp-ser n] [random n] [admin n]}


An example for host-specific weights follows:

ip director host www-servers.sleet.com weights drp-ext 80 random 10 
admin 10

An example for metric priorities follows:

ip director host www-servers.sleet.com priority drp-ext 1 admin 2 random 3

Because there is no default prioritization, all metrics with nonzero weights are considered at the same time and after all other prioritized metrics. Metric priorities must be explicitly configured.

See the section "Setting Metrics and the Server Connection Parameter" in the chapter "" for more information.

You might want to configure DRP-associations, host-specific weights, and priorities in the Director's default DNS server. This may be useful if you use scripting tools to generate and maintain your DNS configurations.

See the "" chapter for more information.

Set Up Server Preferences

To set a preference for a distributed server based on cost, perform the following task in global configuration mode:

Task
Command

Assign a preference for a distributed server (host).

ip director server {hostname | host-ip-address} preference [cost]


For example, to set a preference in the Director for the distributed server www-west.sleet.com, you might use the following command:

ip director server www-west.sleet.com preference 50

or

ip director server 10.0.0.2 preference 50

This example makes the www-west.sleet.com host less preferred to others because it has a higher "cost" than the others (a cost of 50 in this case).

Configure the Primary DNS Server

Perform these steps to configure the primary DNS server for HTTP session redirector mode:

Task
Command

Step 1 In the DNS tables of the primary DNS server, add an address resource record that associates the Director web-server host name with the Director virtual IP address.

Director-host-name in a Director-virtual-IP-address

Step 2 Add an address-to-name mapping (DNS pointer [PTR]) record that associates the virtual IP address with the Director web-server host name.

virtual-IP-address-spec. in ptr Director-host-name

Perform one of the following steps to bind the IP address of each distributed server with the virtual host name.
 

Step 3 Append the text string "-servers" to the first part of the original virtual host name to create a new virtual hostname.

Add DNS records binding the IP addresses of each of the distributed servers to this new virtual host name.

new-virtual-hostname. in a server-address

Step 4 Bind the distributed server IP addresses to the new virtual host name in the Director itself.

ip host new-virtual-hostname address1 [address2...addressn]


For example, the following record associates the host name www.sleet.com with the Director virtual IP address 10.0.0.4:

www.sleet.com. in a 10.0.0.4

Client web browsers requesting service from www.sleet.com will connect to this Director.

An example of a record that associates the virtual IP address 10.0.0.4 with the Director web-server host name www.sleet.com follows:

4.0.0.10.in-addr.arpa. in ptr www.sleet.com.

An example showing the addition of "-servers" and their bindings in the DNS record follows:

www-servers.sleet.com.	 in a 10.0.0.2
www-servers.sleet.com. in a 11.0.0.2
www-servers.sleet.com. in a 12.0.0.2

An example showing the Director's configuration that binds the distributed server IP addresses to the virtual host name follows:

ip host www-servers.sleet.com 10.0.0.2 11.0.0.2 12.0.0.2

Test the Configuration

You can test the HTTP session redirector configuration by accessing the URL (for example, http://www.sleet.com) and noticing to which URL you are connected.

You can test this functionality at a low level by using Telnet. For example, enter the following command to connect to the web redirector server:

telnet www.sleet.com 80

Next, issue a simple HTTP command, such as:

GET /

In reply, you should receive a message similar to the following, after which the connection closes:

HTTP/1.0 302 Webredirector
Location: http://11.0.0.2/
Content-type: text/html

HTML-document

Sample Configuration

This section shows a sample configuration for HTTP session redirector mode, using the network arrangement in .

Figure 7-1 Sample Network Arrangement

How the Configuration Works

Here is an overview of how the Director functions in HTTP session redirector mode:

1 A client web browser tries to retrieve URL http://www.sleet.com.

2 The Internet DNS system maps this name to the Director virtual IP address 10.0.0.4.

3 The Director listens for HTTP connections to IP address 10.0.0.4.

4 The client web browser connects to IP address 10.0.0.4.

5 The Director performs a lookup for the host name associated with the address 10.0.0.4.

6 The Director performs a lookup for the IP addresses associated with the host name www-servers.sleet.com. This results in the normal Director sorting of addresses using all of the metrics configured for this host name.

7 The Director then constructs the new URL using the IP address of the discovered "best" web server (for example, http://12.0.0.2) appended with the rest of the original URL, and sends the web client the code "302 Temporarily Moved," specifying the new URL location.

If the URL originally requested had been:

http://www.sleet.com/Weather/index.html

Then the new URL would be:

http://12.0.0.2/Weather/index.html

8 The client web browser receives the temporary relocation code and transparently connects to the web server at the specified URL.

Because this is only a temporary relocation, the client web browser should bookmark the original URL (http://www.sleet.com), so users who later return to this URL will once again be connected to the "best" web server for that moment. (In reality, most browsers do not bookmark the correct URL. Browser vendors are likely to fix this behavior.)

Sample Director Configuration

After configuring the Ethernet interface, you might enter the following commands to configure the Director.

The Director must listen for connections on one or more virtual IP addresses, in this example 10.0.0.4 (the virtual IP address must be on the same subnet as that of the Director's interface address):

ip director ip-address 10.0.0.4

This command tells the Director to listen for HTTP connections to port 80 at this IP address. The IP address must be a valid, unused address for the subnet to which the Director is connected.

Configure the Director with the location of the DNS server that the Director should retrieve DNS resource records from. You should use the primary sleet.com DNS server:

ip name-server 10.0.0.10

If desired, configure default weights with the following command:

ip director default-weights drp-int 10 drp-ext 90

Default weights are used for all host names sorted by the Director. To override default weights for a certain host, you would specify host-specific weights as described in the next section.

When the associated metric is referenced in the sorting decision, it will always be multiplied by the appropriate metric weight. In this way, you can specify that some metrics should weigh more heavily than others. You may determine the weights you want to use through experimentation. The weights given do not need to add up to 100.

Set up security next.

To set up an access list, you would enter these commands:

access-list 1 permit 10.0.0.2 
access-list 1 permit 11.0.0.2 
access-list 1 permit 12.0.0.2 
access-list 1 deny any

Enter the following interface configuration command to enable the access list:

ip drp access-group 1

Specify the host names that the Director should sort:

ip director access-list 1 permit "^www." 
ip director access-list 1 deny any

Enter the following interface configuration command to tell the Director to use the access list:

ip director access-group 1

To set up MD5 authentication with passwords, you must first set up a key chain with a sequence of commands like the following:

key chain violet 
key 5 
key-string carnation 
exit 

This sets up an authentication key chain containing one key. Then make this the DRP authentication key chain with the following command:

ip drp authentication key-chain violet

This key must be the same as that configured on the DRP server agents to which the Director needs to communicate.

Sample DRP-Associations, Host-Specific Weights, Priorities, and Preferences on the Director

You could use the following commands to configure parameters on the Director:


ip director server 10.0.0.2 drp-association 10.0.0.3
ip director server 11.0.0.2 drp-association 11.0.0.3
ip director server 12.0.0.2 drp-association 12.0.0.3

The preceding commands tell the Director which DRP server agents are associated with each distributed server.

You could either use IP addresses (as shown) or use host names, as follows (see ):

ip director server www-1.sleet.com drp-association drp-1.sleet.com
ip director server www-2.sleet.com drp-association drp-2.sleet.com
ip director server www-3.sleet.com drp-association drp-3.sleet.com

The Director will query its default DNS server for name-to-address bindings. If you use host/router names instead of IP addresses, you must make sure to configure the appropriate A records in the Director's default DNS server. You should use your primary domain server as the Director's default DNS server to ensure that all such name-to-address binding requests can be satisfied.

You could also configure the IP addresses of the hosts shown with the following commands in the Director:

ip host www-1.sleet.com 10.0.0.2
ip host www-2.sleet.com 11.0.0.2
ip host www-3.sleet.com 12.0.0.2
ip host drp-1.sleet.com 10.0.0.3
ip host drp-2.sleet.com 11.0.0.3
ip host drp-3.sleet.com 12.0.0.3

In any case, make sure to configure the appropriate A records for such host names in your primary server so that external queries will receive correct DNS responses.

To add host-specific weights, you would add more information to the Director. For example, you could configure host-specific weights like this:

ip director host www-servers.sleet.com weights drp-ext 80 random 10 
admin 10

The weights do not need to add up to 100. When the associated metric is referenced in the sorting decision, it will always be multiplied by the appropriate metric weight. In this way, you can specify that some metrics should weigh more heavily than others.

To use metric priority, you could use this configuration on the Director:

ip director host www-servers.sleet.com priority drp-ext 1 admin 2

With this configuration, all clients would be assigned to the server that is closest to them according to BGP hop count distance. If two or more servers are at the same distance, the choice should be according to administrative preference.

You could set up some an administrative preference with the following command:

ip director server www-west.sleet.com preference 50

This example makes the www-west.sleet.com host less preferred to others because it has a higher "cost" than the others (a cost of 50 in this case).

For more information, refer to the section "Setting Metrics and the Server Connection Parameter" in the chapter "."

Sample Primary DNS Server

The steps below configure a primary DNS server for the sleet.com domain.


Step 1 You need the following records on the primary DNS server for the sleet.com domain:

www.sleet.com.	 in	 a 10.0.0.4
4.0.0.10.in-addr.arpa. in ptr www.sleet.com.

The first record is passed to the Internet as the standard IP address for the www.sleet.com server. Clients will connect to the Director at this address. The Director then queries for the DNS host name associated with the 10.0.0.4 address and receives www.sleet.com through the second record.

Step 2 Add the following DNS records to the primary domain DNS server:

www-servers.sleet.com. in a 10.0.0.2
www-servers.sleet.com. in a 11.0.0.2
www-servers.sleet.com. in a 12.0.0.2

or

Bind the distributed server IP addresses to the virtual host name in Director itself using the ip host command:

ip host www-servers.sleet.com 10.0.0.2 11.0.0.2 12.0.0.2

These commands define the IP addresses associated with the www-servers.sleet.com for the Director. The Director will embed one of these IP addresses in a URL, and return it, along with an HTTP status code 302, to the requesting client, thus redirecting the client to the best server.