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Article Information

This article applies to the following ZCS versions.

ZCS 8.0 Article ZCS 8.0

DoSFilter Throttling Mechanism

The denial-of-service filter or DoSFilter was added to the mailbox server in ZCS 8.0 to throttle clients sending a large number of requests over a very short period of time. The DoSFilter is applied to all requests for service, mailbox and admin. This feature was added with the completion of bug 66921.

DoS filtering is enabled by default once ZCS 8 is installed. It may be necessary to adjust the configuration to accommodate specific environmental needs. Disabling DoSFilter is not recommended.

Identifying False Positives

It is possible for clients such as Zimbra Connector for Outlook (ZCO), mobile ActiveSync, zmprov, etc. to trigger the DoSFilter. To the client, the Zimbra mailbox service is unavailable. DoSFilter can be identified on the server in the following ways:


2013-01-15 15:52:20,426 WARN [qtp1635701107-91:][;mid=64;ip=;Cmd=FolderSync;DeviceID=Appl5K0113UN3NR;Version=12.1;] sync - Service exception
com.zimbra.common.service.ServiceException: error while proxying request to target server: HTTP/1.1 503 Service Unavailable
ExceptionId:qtp1635701107-91: Code:service.PROXY_ERROR Arg:(url, STR,\"\")


2013-01-15 15:57:32.537:WARN:oejs.DoSFilter:DOS ALERT:ip=,session=null,user=null


The configuration attributes zimbraHttpDosFilterDelayMillis, zimbraHttpDosFilterMaxRequestsPerSec and zimbraHttpThrottleSafeIPs. Each attribute is server inherited from global or is configurable at the sever level. Our recommendation is to preserve the default configuration whenever possible.

DoSFilter Delay (milliseconds) - zimbraHttpDosFilterDelayMillis

Delay imposed on all requests over the rate limit, before they are considered at all. -1 = Reject request, 0 = No delay, any other value = Delay in ms. The default is -1.

To modify in the global configuration; e.g. set the delay to 20ms:

zmprov mcf zimbraHttpDosFilterDelayMillis 20

DoSFilter Maximum Requests Per Second - zimbraHttpDosFilterMaxRequestsPerSec

Maximum number of requests from a connection per second. Requests in excess of this are throttled. The default is 30 and the minimum is 1.

To set the maximum number for requests in the global configuration:

zmprov mcf zimbraHttpDosFilterMaxRequestsPerSec 100

DoSFilter IP Addresses Whitelist - zimbraHttpThrottleSafeIPs

IP addresses to ignore when applying Jetty DosFilter. This attribute does not have a default value, however these loopback IPs are whitelisted by default:

  • ::1

IP addresses should be comma separated. To modify:

zmprov mcf zimbraHttpThrottleSafeIPs,

Mailbox server restart

A mailbox server restart is required when modifying these attributes.

zmmailboxdctl restart

Tuning Considerations - 8.0.3 and later

ZCS Member Servers

ZCS servers under the control of a single master LDAP server are automatically whitelisted by IP address. These hosts are discovered using a GetAllServersRequest call; i.e., zmprov gas.

External Provisioning Hosts/SOAP API

External provisioning hosts may be added to the IP whitelist to ensure DoSFilter does not block some requests. For example, a mailbox reindex may make several calls per second that can trigger DoSFilter.

ZCS 8.0.0 - 8.0.2

See this link on the Zimbra forums for information on configuring DoSFilter for ZCS 8 versions prior to 8.0.3.

Verified Against: ZCS 8.0.x Date Created: 03/20/2013
Article ID: Date Modified: 2013-03-25

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