Bug 1193578

Summary: IdM Client does not set udp_preference_limit on upgrade - may affect clients with 2FA authentication
Product: Red Hat Enterprise Linux 7 Reporter: Martin Kosek <mkosek>
Component: ipaAssignee: IPA Maintainers <ipa-maint>
Status: CLOSED WONTFIX QA Contact: Namita Soman <nsoman>
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: 7.1CC: apetrova, mnavrati, rcritten
Target Milestone: rc   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: Doc Type: Known Issue
Doc Text:
Kerberos libraries on Identity Management clients communicate by default over the User Datagram Protocol (UDP). Using a one-time password (OTP) can cause additional delay, which can result in breaching Kerberos timeouts. As a consequence, the kinit command an other Kerberos operations can report communication errors, and the user can get locked out. To work around this problem, make communication using the slightly slower Transmission Control Protocol (TCP) default by setting the "udp_preference_limit" option to 0 in the /etc/krb5.conf file.
Story Points: ---
Clone Of: Environment:
Last Closed: 2015-02-17 15:53:09 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:

Description Martin Kosek 2015-02-17 15:51:05 UTC
This bug is filed to log a Known Issue for feature tracked in Bug 919228 and in upstream ticket https://fedorahosted.org/freeipa/ticket/4725.

Changes done in Bug and Ticket involved setting "udp_preference_limit" setting in /etc/krb5.conf for new IdM Client or IdM Server installations. This setting forces Kerberos to operate on TCP protocol instead of UDP protocol which does is more resilient to longer processing time on the server if OTP is used (especially if OTP authentication is redirected to external OTP server via Radius protocol).

New RHEL-7.1 IdM clients are fixed and have the value as default. However, it was decided not do update krb5.conf on RHEL-7.0 to 7.1 upgrades. Users who want to use OTP and are just upgrading existing IdM RHEL-7.0 clients are encouraged to update this configuration manually:

/etc/krb5.conf:
...
[libdefaults]
...
 udp_preference_limit = 0
...