Ou work for a large software company in seattle. they have their production environment provisioned on aws inside a custom vpc. the vpc contains both a public and private subnet. the company tests their applications on custom ec2 instances inside a private subnet. there are approximately 500 instances, and they communicate to the outside world via a proxy server. at 3am every night, the ec2 instances pull down os updates, which are usually 150mb or so. they then apply these updates and reboot: if the software has not downloaded within half an hour, then the update will attempt to download the following day. you notice that a number of ec2 instances are continually failing to download the updates in the allotted time. which of the following answers might explain this failure?