During the life of a persistent connection, the Cisco Content Services
Switch (CSS) determines when to move a client connection to a new service based
on content rules, load balancing, and service availability. Some situations do
not require moving the client connection; in others, it is mandatory. This
document describes how to configure the CSS to make these decisions using the
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Cisco Technical Tips
There are no specific prerequisites for this document.
This document is not restricted to specific software and hardware
The information presented in this document was created from devices in
a specific lab environment. All of the devices used in this document started
with a cleared (default) configuration. If you are working in a live network,
ensure that you understand the potential impact of any command before using
When a CSS receives a request for content from a client, the software
compares the request to a content rule and determines which service handles the
request. If the request matches a content rule, the CSS establishes a client
connection to the service specified by the content rule. By default, the CSS
keeps the client on the same connection for an entire flow session as long as a
new content request meets the following conditions:
Matches the same content rule that specified the current service.
Matches a new content rule that contains the current service, even if
a different service is specified by the content rule.
Does not match a content rule, but a previous content rule match
connected the client to the current service.
This CSS behavior is known as content rule persistence. When using
transparent caches, which pre-fetch content, or mirrored content servers, this
scheme works because the same content is available on each service.
The persistent command in content
configuration mode maintains a persistent connection with a server as long as
the above criteria is met. Persistence is enabled by default. Disabling
persistence allows the CSS to move a connection to a better service on the same
rule or utilize cache bypass functionality, Extension Qualifier Lists (EQLs),
or failover bypass. The no persistent command should
be configured on a content rule with the following:
A balance method of domain or domain hash when using proxy caches.
A method of url or urlhash when using transparent caches.
A failover method of bypass when using transparent caches.
An EQL bypass using transparent cache.
Adding a sorry server to a content rule.
Issue the following command to enable persistence:
Issue the following command to disable persistence:
config-owner-content)# no persistent
The CSS redirects a request for content on a persistent connection if
it matches a new content rule that does not contain the current service, or if
persistence is disabled and there is a better service configured in the rule.
The CSS redirects or remaps the current connection to a new service based on
the persistence reset command setting if the command
is configured. If the persistence reset command is
not configured, the CSS performs a HTTP redirect by default.
If a CSS bypasses a service (for example, with transparent cache down
and failover bypass configured) when the next content request on the same TCP
connection matches a content rule that contains the down transparent cache, the
CSS will continue to bypass the cache, by default, even after the bypassed
service is back online. In this case, the CSS typically sends the content
request to the origin server. This behavior is called bypass
Configure the CSS to redirect or remap a bypassed connection using the
bypass persistence global configuration command in
conjunction with the persistence reset
Issue the bypass persistence command to
determine if the CSS redirects or remaps operation properly. The CSS should
redirect to reset a bypassed service when a content request matches a content
rule and a previous request caused the bypass. This global command affects all
Bypass persistence is enabled by default with the following
(config)# bypass persistence disable
CSS redirects or remaps to reset the connection according to the
setting of the persistence reset method.
(config)# bypass persistence enable
CSS does not redirect or remap to reset the connection and continues to
bypass a service.
Content rule persistence is not useful when placing different content
on different servers (for example, to conserve server disk space for load
balancing considerations, or when using proxy caches). Disable persistence by
issuing the no persistent command in these
When the CSS receives a client request for content not available on the
current service, reset the connection to the current service and establish a
new connection to the service containing the requested content, (for example, a
different proxy cache or the origin server). This is accomplished by one of the
Redirection: An HTTP technique that resets the
client-to-CSS (front end) connection and the CSS-to-service (back end)
connection, then establishes a new flow to the best service containing the
Service Remapping: A technique that resets the back
end connection and moves the back end connection to the best service containing
the requested content. This technique is faster and more efficient than
redirection since the CSS does not reset and reestablish the front end
connection. With service remapping, the CSS strictly manages port mapping to
prevent the occurrence of duplicate port numbers.
Service remapping is used when moving the back end connection satisfies
the content request and rule match. The CSS uses redirect to move the client
connection to a new VIP address and/or port.
When resetting a connection to a new back end service, issue the
persistence reset command with the no
persistent command to cause an HTTP redirection or perform a back
end remapping operation. This global command affects all flow setups that
require redirecting or remapping.
Issue the following command to enable redirection:
(config)# persistence reset redirect
Issue the following command to enable service remapping:
(config)# persistence reset remap
The CSS does not use remapping when selecting redirect type services.
Issue the show remap command to display the
configured persistence reset and bypass persistence settings and to view the
megamaps used. This command is available in all modes.
# show remap
Persistence Reset Method: Redirect
Bypass Persistence: Disabled