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1.? Introduction to session persistence profiles

Using BIG-IP Local Traffic Manager,you can configure session persistence. When you configure session persistence,Local Traffic Manager tracks and stores session data,such as the specific pool member that serviced a client request. The primary reason for tracking and storing session data is to ensure that client requests are directed to the same pool member throughout the life of a session or during subsequent sessions.

In addition,session persistence can track and store other types of information,such as user preferences or a user name and password.

Local Traffic Manager offers several types of session persistence,each one designed to accommodate a specific type of storage requirement for session data. The type of persistence that you implement depends on where and how you want to store client-specific information,such as items in a shopping cart or airline ticket reservations.

For example,you might store airline ticket reservation information in a back-end database that all servers can access,or on the specific server to which the client originally connected,or in a cookie on the client’s machine. When you enable persistence,returning clients can bypass load balancing and instead connect to the server to which they last connected in order to access their saved information.

Local Traffic Manager keeps session data for a period of time that you specify.

The primary tool for configuring session persistence is to configure a persistence profile and assign it to a virtual server. If you want to enable persistence for specific types of traffic only,as opposed to all traffic passing through the virtual server,you can write an iRule.

A persistence profile is a pre-configured object that automatically enables persistence when you assign the profile to a virtual server. By using a persistence profile,you avoid having to write a program to implement a type of persistence.

Each type of persistence that Local Traffic Manager offers includes a corresponding default persistence profile. These persistence profiles each contain settings and setting values that define the behavior of the BIG-IP system for that type of persistence. You can either use the default profile or create a custom profile based on the default.

2.? Persistence profile types

You can configure persistence profile settings to set up session persistence on the BIG-IP system. You can configure these settings when you create a profile or after profile creation by modifying the profile’s settings.?

The persistence types that you can enable using a persistence profile are:

Cookie persistence

Cookie persistence uses an HTTP cookie stored on a client’s computer to allow the client to reconnect to the same server previously visited at a web site.

Destination address affinity persistence

Also known as sticky persistence,destination address affinity persistence supports TCP and UDP protocols,and directs session requests to the same server based solely on the destination IP address of a packet.

Hash persistence

Hash persistence allows you to create a persistence hash based on an existing iRule.

Microsoft Remote Desktop Protocol persistence

Microsoft Remote Desktop Protocol (MSRDP) persistence tracks sessions between clients and servers running the Microsoft Remote Desktop Protocol (RDP) service.

SIP persistence

SIP persistence is a type of persistence used for servers that receive Session Initiation Protocol (SIP) messages sent through UDP,SCTP,or TCP.

Source address affinity persistence

Also known as simple persistence,source address affinity persistence supports TCP and UDP protocols,and directs session requests to the same server based solely on the source IP address of a packet.

SSL persistence

SSL persistence is a type of persistence that tracks SSL sessions,using the SSL session ID. Even when the client’s IP address changes,Local Traffic Manager still recognizes the connection as being persistent based on the session ID.

Universal persistence

Universal persistence allows you to write an expression that defines what to persist on in a packet. The expression,written using the same expression syntax that you use in iRules,defines some sequence of bytes to use as a session identifier.

3.? Session persistence and iRules

Instead of configuring a persistence profile,which enables a persistence type for all sessions passing through the virtual server,you can write an iRule,which enables a persistence type for particular requests (for example,for HTTP traffic that includes a certain cookie version only).

You can also use an iRule to enable persistence for SSL-terminated requests,that is,requests that Local Traffic Manager terminates by performing decryption and re-encryption and by handling SSL certificate authentication. In iRules of this type,you can use an HTTP header insertion iRule command to insert an SSL session ID as a header into an HTTP request.

4.? The OneConnect profile and session persistence

The Request-URI header in an HTTP request stores certain session data. Occasionally,however,for Cookie and Universal persistence types specifically,Local Traffic Manager ignores the session data in this header,and sends requests to an unexpected node. For example,this issue can occur when clients send requests to a virtual server through an internet proxy device. You can prevent this problem by creating a OneConnect profile,and assigning both the OneConnect profile and the persistence profile to the virtual server.

5.? HTTP parsing with and without a OneConnect profile

If the virtual server does not reference a OneConnect profile,Local Traffic Manager performs load balancing for each TCP connection. Once the TCP connection is load balanced,the system sends all requests that are part of the connection to the same pool member.

For example,if the virtual server does not reference a OneConnect profile,and Local Traffic Manager initially sends a client request to node A in pool A,the system inserts a cookie for node A. Then,within the same TCP connection,if Local Traffic Manager receives a subsequent request that contains a cookie for node B in pool B,the system ignores the cookie information and incorrectly sends the request to node S instead.

Using a OneConnect type of profile ensures that the BIG-IP system does not ignore session data. If the virtual server references a OneConnect profile,Local Traffic Manager can perform load balancing for each request within the TCP connection. That is,when an HTTP client sends multiple requests within a single connection,Local Traffic Manager is able to process each HTTP request individually. Local Traffic Manager sends the HTTP requests to different destination servers if necessary.

For example,if the virtual server references a OneConnect profile and the client request is initially sent to node A in pool A,Local Traffic Manager inserts a cookie for node A. Then,the system uses that cookie information and correctly sends the request to node B.

6.? Criteria for session persistence

Regardless of the type of persistence you are implementing,you can specify the criteria that the BIG-IP system uses to send all requests from a given client to the same pool member. These criteria are based on the virtual server or servers that are hosting the client connection. To specify these criteria,you use the Match Across Services,Match Across Virtual Servers,and Match Across Pools profile settings. Before configuring a persistence profile,it is helpful to understand these settings.

7.? Destination address affinity persistence

You can optimize your server array with destination address affinity persistence. Destination address affinity persistence,also known as sticky persistence,directs requests for a certain destination IP address to the same server,regardless of which client made the request.

This type of persistence provides the most benefits when load balancing caching servers. A caching server intercepts web requests and returns a cached web page if it is available. In order to improve the efficiency of the cache on these servers,it is necessary to send similar requests to the same server repeatedly. You can use the destination address affinity persistence type to cache a given web page on one server instead of on every server in an array. This saves the other servers from having to duplicate the web page in their cache,wasting memory.

?8.? Hash persistence

Hash persistence allows you to create a persistence hash based on an existing iRule that uses the persist iRule command. Using hash persistence is the same as using universal persistence,except that with hash persistence,the resulting persistence key is a hash of the data,rather than the data itself.?

An example of a iRule that implements hash persistence:?

rule my_persist_irule { when HTTP_REQUEST { persist hash [HTTP::header myheader] } }

Note that if you use hash persistence and Local Traffic Manager cannot find an entry in the persistence table for a connection,and the system has not yet chosen a pool member due to fallback persistence,then the system uses the hash value,rather than the specified load balancing method,to select the pool member.?

For example,if the persistence table contains no entry for the hash value 2356372769,and the number of active nodes in the pool remains the same,then a session with that hash value for persistence is always persisted to node 10.10.10.190 (assuming that the node is active).

• 9.? Microsoft Remote Desktop Protocol persistence

MSRDP persistence provides an efficient way of load balancing traffic and maintaining persistent sessions between Windows clients and servers that are running the Microsoft Remote Desktop Protocol (RDP) service. The recommended scenario for enabling MSRDP persistence feature is to create a load balancing pool that consists of members running Windows Server 2003 or Windows Server 2008,where all members belong to a Windows cluster and participate in a Windows session directory.?

10. Benefits of Microsoft Remote Desktop Protocol persistence?

Normally,Windows servers running Microsoft Terminal Services can use a session broker (known as Terminal Services Session Directory in Windows Server 2003 and TS Session Broker in Windows Server 2008) to ensure that user sessions are assigned to specific servers. If a client initiates a connection request to the wrong terminal server,that server redirects the client to the appropriate server.?

When you have a BIG-IP system,the incorrect server needs to redirect the client to the BIG-IP system virtual server,rather than to an individual server in the load balancing pool. To ensure that this happens,you can configure an MSRDP profile. With an MSRDP profile,Local Traffic Manager uses a token that the session broker provides to maintain persistence records. If a user initiates a session for which no session broker token exists,Local Traffic Manager makes load balancing decisions according to whichever load balancing method is configured for the pool.?

In summary,using Local Traffic Manager with an MSRDP persistence profile,in conjunction with a session broker,allows for higher scalability and a greater range and flexibility of load balancing options than when using a session broker alone.?

Microsoft Remote Desktop Protocol persistence server platform issues?

By default,Local Traffic Manager with MSRDP persistence enabled load balances connections according to the way that the user has configured Local Traffic Manager for load balancing,as long as the session broker is configured on each server in the pool. Terminal Services Session Directory and TS Session Broker are features that are only available on Windows Server 2003 or Windows Server 2008 respectively. Therefore,each server in the pool must be a Windows Server 2003 or Windows Server 2008 server,if you want to use MSRDP persistence in default mode. Also,each client system must be running the remote desktop client software that is included with any Windows Server 2003 or Windows Server 2008 system.?

If,you want to enable MSRDP persistence but your server platforms are running older versions of Windows (on which Session Directory or TS Session Broker is not available),you can enable MSRDP persistence in non-default mode. This causes Local Traffic Manager to connect a client to the same Windows server by way of the user name that the client provides. Note that enabling MSRDP persistence in non-default mode (that is,with no session broker available on the servers) is less preferable than the default mode,because it provides limited load-balancing and redirection capabilities.?

Configuring MSRDP persistence with a session broker

To enable MSRDP persistence in the default mode,you must configure a session broker on each Windows server in your load balancing pool. In addition to configuring a session broker,you must perform other Windows configuration tasks on those servers. However,before you configure your Windows servers,you must configure Local Traffic Manager,by performing tasks such as creating a load-balancing pool and designating your Windows servers as members of that pool.?

Configuring MSRDP persistence without a session broker

When a server has no session broker,the server cannot share sessions with other servers,and therefore cannot perform any redirections when a connection to a server becomes disconnected. In lieu of session sharing,Windows clients provide data,in the form of a user name,to the BIG-IP system to allow the BIG-IP system to consistently connect that client to the same server. Enabling MSRDP persistence to behave in this way is the non-default mode.

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12. SIP persistence

Session Initiation Protocol is an application-layer protocol that manages sessions consisting of multiple participants,thus enabling real-time messaging,voice,data,and video. A session can be a simple two-way telephone call or Instant Message dialogue,or a complex,collaborative,multi-media conference call that includes voice,and video. With SIP,applications can communicate with one another by exchanging messages through the SCTP,TCP or UDP protocols.?

SIP persistence is a type of persistence available for server pools. You can configure SIP persistence for proxy servers that receive SIP messages sent through the UDP profile. Local Traffic Manager currently supports persistence for SIP messages sent through the UDP,TCP,or SCTP protocols.?

Important: For virtual servers processing UDP traffic,always check that the value of the SIP profile Timeout setting is at least as long (in seconds) as the value of the Idle Timeout setting of the UDP profile. Doing so ensures that SIP traffic is persisted properly.

13. Source address affinity persistence

Source address affinity persistence,also known as simple persistence,tracks sessions based only on the source IP address. When a client requests a connection to a virtual server that supports source address affinity persistence,Local Traffic Manager checks to see if that client previously connected,and if so,returns the client to the same pool member.?

You might want to use source address affinity persistence and SSL persistence together. In situations where an SSL session ID times out,or where a returning client does not provide a session ID,you might want Local Traffic Manager to direct the client to the original pool member based on the client’s IP address. As long as the client’s source address affinity persistence record has not timed out,Local Traffic Manager can successfully return the client to the appropriate pool member.?

Persistence settings apply to all protocols. When the persistence timer is set to a value greater than 0,persistence is on. When the persistence timer is set to 0,persistence is off.?

The persistence mask feature works only for virtual servers that implement source address affinity persistence. By adding a persistence mask,you identify a range of source IP addresses to manage together as a single source address affinity persistent connection when connecting to the pool.

14. SSL persistence

SSL persistence is a type of persistence that tracks SSL sessions using the SSL session ID,and it is a property of each individual pool. Using SSL persistence can be particularly important if your clients typically have translated IP addresses or dynamic IP addresses,such as those that Internet service providers typically assign. Even when the client’s IP address changes,BIG-IP system still recognizes the session as being persistent based on the session ID.?

You might want to use SSL persistence and source address affinity persistence together. In situations where an SSL session ID times out,you might want the BIG-IP system to direct the client to the original node based on the client’s IP address. As long as the client’s simple persistence record has not timed out,the BIG-IP system can successfully return the client to the appropriate node.

15. Universal persistence

Included in the Local Traffic Manager Universal Inspection Engine (UIE) is a set of functions that you can specify within BIG-IP system iRules to direct traffic in more granular ways. Using these iRule functions,you can write expressions that direct traffic based on content data,or direct traffic to a specific member of a pool.

Universal persistence takes this iRules feature one step further,by allowing you to use the iRule persist uie command to implement persistence for sessions based on content data,or based on connections to a specific member of a pool. Universal persistence does this by defining some sequence of bytes to use as a session identifier.

To use iRule expressions for persistence,a universal persistence profile includes a setting that specifies the name of the iRule containing the expression.

rule my_persist_irule { when HTTP_REQUEST { persist uie [HTTP::header myheader] } }

Unlike hash persistence,which uses a hash of the data as the persistence key,universal persistence uses the data itself as the persistence key.

Note: F5 Networks recommends that you configure a OneConnect profile in addition to the Universal profile,to ensure that Local Traffic Manager load balances HTTP requests correctly.