Initial version of Cisco CSR1000v 3.13 (csr1000v-universalk9.03.13.00.S.154-3.S-ext) was broken and kept crashing while booting on VMware ESXi 5.1, but apparently does work on ESXi 5.5. Cisco has silently replaced it with 3.13S0a version (csr1000v-universalk9.03.13.00a.S.154-3.S0a-ext) without providing any release notes or even updating filedates. Which is exactly as broken as old one - stuck in infinite reboot loop. Download is here , but for some reason for 3.13 only OVA packaged one is available after free registration. If you need ISO simply unpack OVA with 7zip and use ISO you can find inside for install. And then it will fail. Perhaps something to do with crazy nested virtualization CSR uses. Thanks guys.