[FROG] IS-IS on libvirt

among our test environments, we have a libvirt setup. we're having some un-fun with IS-IS interoperation, and trying to isolate the issue. to complicate things, the libvirt has jumbogram veths. the same devices work with real hardwarem, though with 1500 MTUs. anyone been in the libvirt/IS-IS space and have some clues? randy