Prefer TCP connections to UDP in krb5 clients

In general, TCP is a better fit for FreeIPA due to large packet sizes.

However, there is also a specific need for TCP when using OTP. If a UDP
packet is delivered to the server and the server takes longer to process
it than the client timeout (likely), the OTP value will be resent.
Unfortunately, this will cause failures or even lockouts. Switching to
TCP avoids this problem altogether.

https://fedorahosted.org/freeipa/ticket/4725

Reviewed-By: Martin Kosek <mkosek@redhat.com>

install/share/krb5.conf.template

@@ -12,6 +12,7 @@ includedir /var/lib/sss/pubconf/krb5.include.d/
  rdns = false
  ticket_lifetime = 24h
  forwardable = yes
+ udp_preference_limit = 0
 $OTHER_LIBDEFAULTS
 [realms]
  $REALM = {

install/tools/ipa-replica-conncheck

@@ -208,6 +208,7 @@ def configure_krb5_conf(realm, kdc, filename):
     libdefaults.append({'name':'rdns', 'type':'option', 'value':'false'})
     libdefaults.append({'name':'ticket_lifetime', 'type':'option', 'value':'24h'})
     libdefaults.append({'name':'forwardable', 'type':'option', 'value':'yes'})
+    libdefaults.append({'name':'udp_preference_limit', 'type':'option', 'value':'0'})
 
     opts.append({'name':'libdefaults', 'type':'section', 'value': libdefaults})
     opts.append({'name':'empty', 'type':'empty'})

ipa-client/ipa-install/ipa-client-install

@@ -1047,6 +1047,7 @@ def configure_krb5_conf(cli_realm, cli_domain, cli_server, cli_kdc, dnsok,
     libopts.append({'name':'rdns', 'type':'option', 'value':'false'})
     libopts.append({'name':'ticket_lifetime', 'type':'option', 'value':'24h'})
     libopts.append({'name':'forwardable', 'type':'option', 'value':'yes'})
+    libopts.append({'name':'udp_preference_limit', 'type':'option', 'value':'0'})
 
     # Configure KEYRING CCACHE if supported
     if kernel_keyring.is_persistent_keyring_supported():