Which persistence options are available for an L7 TCP vService?

Short answer

On the L7 TCP vService, the Persistence field has only None (default) and Hash. Hash creates a key with connection-level Smart Variables such as the client IP, SNI, destination IP and port, RDP cookie and JA4, and keeps the key → Backend Service mapping in a table on the device. For RDP traffic, there is also the RDP Cookie algorithm, which provides persistence itself; when it is selected, the Persistence field is hidden. New Cookie, Current Cookie, SAM and the Source algorithm are only on the HTTP vService.

Options

Option	How it works	Suitable case
None	Each connection is distributed independently according to the algorithm	Database pools, stateless TCP services
Hash	The key → Backend Service mapping is kept in a table; Hash Key List Size default 3,000,000 records, Hash Key Expire Time default 7 days	The connections of the same client must go to the same Backend Service
RDP Cookie algorithm (Self-persistent)	The Backend Service is selected with the hash of the cookie in the RDP connection (the one specified in the RDP Cookie Name field); the Hash Consistency field also appears	RDP server farms

Key Examples for Hash

Key	Scenario
Client IP address	All connections of the same client to the same server
SNI	In TLS pass-through, by the target domain name
Destination IP + port	Setups in which multiple destinations are gathered on the same vService
RDP cookie (mstshash)	RDP; the mapping is kept in the table
JA4	By the TLS client fingerprint

The list is based on the common keys in the docs.

In TR7

• Location: Load Balancer → Load Balancer vService List → L7 TCP vService → Edit → Details → LB Algorithm box → Persistence; when Hash is selected, Hash Key, Hash Key List Size and Hash Key Expire Time appear. It is saved with Save.
• RDP Cookie: It is selected in the Algorithm field; RDP Cookie Name is required (RDP Cookie). When it is selected, the Persistence field is hidden.
• Hash table: It is device-local; it is not shared between cluster devices and is reset when the vService is reloaded (Does saving a configuration change reset the persistence tables?). The settings, however, are transferred to the peer device automatically while Clustering is on and Manual Sync Mode is off (default).

Common Misconceptions

• "In L7 TCP, IP persistence is provided with the Source algorithm." Source is only in HTTP; in L7 TCP, Hash + the client IP address is used.
• "I use cookie persistence in TLS traffic." Since L7 TCP does not process the HTTP layer, the cookie is not read; an HTTP vService is required for the cookie methods.
• "I turn on Hash together with RDP Cookie." When RDP Cookie is selected, the Persistence field is hidden.

How it is done in the documentation

• L7 TCP vService · Session Persistence
• L7 TCP vService · RDP Cookie
• L7 TCP vService · Algorithms

Related questions

• How does Hash persistence work?
• What is the RDP Cookie algorithm?
• Which persistence methods are available?