this is common issue on SLES vm on ESX, if you choose automatic upgrade, it may have a chances to reboot your vm once the vmtools is been upgraded. Alternatively, you should do manual interaction vmtools upgrade, and recompile the kernel on the SLES, and restart the network services. This can prevent your VM is been rebooted.
Craig
vExpert 2009
Malaysia VMware Communities -
Craig
vExpert 2009 & 2010
Netapp NCIE, NCDA 8.0.1
Malaysia VMware Communities - http://www.malaysiavm.com