After applying ESXi 5.5 patch ESXi550-201410401-BG or ESXi 5.1 ESXi510-201410401-BG, the Citrix NetScaler lost network connectivity after running for a few minutes. I think that this also applies to patches released after this.
There was a workaround published by Citrix and VMware in some KB's. heres the link to the VMware KB: KB2092809
Citrix has now released a new version/build 10.5.55.8 that solves the problem, See the release notes: http://www.citrix.com/content/dam/citrix/en_us/documents/downloads/netscaler-adc/NS_10_5_55_8.html