After we upgraded to 1.2.12, we've been having issues with libvirt... it complains that our formerly valid guest definitions are now invalid: error: Failed to start domain XXXX error: internal error: Cannot instantiate filter due to unresolvable variables or unavailable list elements: DHCPSERVER We looked into this, and found that it's the XML validation that's failing: # xmllint --noout --relaxng "/share/libvirt/schemas/domain.rng" XXXX.xml --recover Relax-NG validity error : Extra element devices in interleave test.xml:1: element domain: Relax-NG validity error : Element domain failed to validate content test.xml fails to validate And, a minimal domain XML to reproduce it (this won't boot, but it shows the issue): <domain type='kvm' id='65'> <name>XXXX</name> <uuid>b602b5f2-b9d7-43bd-a949-acc7eeeb9f8f</uuid> <memory unit='KiB'>1048576</memory> <devices> <interface type='bridge'> <filterref filter='myfilter'> <parameter name='CTRL_IP_LEARNING' value='none'/> <parameter name='DHCPSERVER' value='104.156.226.10'/> <parameter name='IP' value='104.207.129.11'/> <parameter name='IP6_ADDR' value='2001:19f0:300:2102::'/> <parameter name='IP6_MASK' value='64'/> </filterref> </interface> </devices> </domain> The cause seems to be having multiple parameters in a <filterref> block. We applied the following patch to fix it: diff -ur src_clean/docs/schemas/domaincommon.rng src/docs/schemas/domaincommon.rng --- src_clean/docs/schemas/domaincommon.rng 2015-01-23 06:46:24.000000000 -0500 +++ src/docs/schemas/domaincommon.rng 2015-03-10 11:30:42.057441342 -0400 @@ -4468,6 +4468,7 @@ <data type="NCName"/> </attribute> <optional> + <zeroOrMore> <element name="parameter"> <attribute name="name"> <ref name="filter-param-name"/> @@ -4476,6 +4477,7 @@ <ref name="filter-param-value"/> </attribute> </element> + </zeroOrMore> </optional> </define>