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Alteon Application Switch Operating System Application Guide
Persistence
584
Document ID: RDWR-ALOS-V2900_AG1302
Using Source IP Address
Using the source IP address as the key identifier was once the only way to achieve TCP/IP session
persistence. There are two major conditions which cause problems when session persistence is
based on a packet's IP source address:
• Many clients sharing the same source IP address (proxied clients)—Proxied clients
appear to Alteon as a single source IP address and do not take advantage of SLB. When many
individual clients behind a firewall use the same proxied source IP address, requests are directed
to the same server, without the benefit of load balancing the traffic across multiple servers.
Persistence is supported without the capability of effectively distributing traffic load.
Also, persistence is broken if you have multiple proxy servers behind Alteon performing SLB.
Alteon changes the client's address to different proxy addresses as attempts are made to load
balance client requests.
• Single client sharing a pool of source IP addresses—When individual clients share a pool
of source IP addresses, persistence for any given request cannot be assured. Although each
source IP address is directed to a specific server, the source IP address itself is randomly
selected, thereby making it impossible to predict which server will receive the request. SLB is
supported, but without persistence for any given client.
Using Cookies
Cookies are strings passed via HTTP from servers to browsers. Based on the mode of operation,
cookies are inserted by either Alteon or the server. After a client receives a cookie, a server can poll
that cookie with a GET command, which allows the querying server to positively identify the client as
the one that received the cookie earlier.
Cookie-based persistence solves the proxy server problem and gives better load distribution at the
server site. In Alteon, cookies are used to route client traffic back to the same physical server to
maintain session persistence.
Note: If the cookie expiration time is greater than the
/cfg/slb/virt x/service x/ptmout
value, timed-out requests will not be persistent.
Using SSL Session ID
The SSL session ID is effective only when the server is running SSL transactions. Because of the
heavy processing load required to maintain SSL connections, most network configurations use SSL
only when it is necessary. Persistence based on the SSL Session ID ensures completion of complex
transactions in proxy server environments. However, this type of persistence does not scale on
servers because of their computational requirements.
Note: SSL session ID persistence is not supported when SSL offloading is enabled and other more
advanced persistency features, such as cookie persistency, are available.
HTTP and HTTPS Persistence Based on Client IP
Alteon lets you use the client IP address to maintain persistence for both HTTP and HTTPS sessions
only. The
pbind clientip
command maintains persistence for the same service across multiple
sessions from the same client, or maintains persistence between different services (for HTTP and