NTP is abbreviation for Network Time Protocol which is used for clock synchronization of various devices on the net. There are three typical implementations of NTP in network infrastructure: a) no implementation b) useful implementation c) vital implementation.

The first option is an indicator that network is in poor condition. It has no real owner or owner isn't a network professional, etc.

The second option is the most common case for serious corporate network. The owner cares about event logging (at least) and event correlation in different parts of network. Complex debugging, security incident investigation requires the "right time" to be set. But still network functioning in general or service availability isn't tied with NTP.

And we have the third option. Vital dependency is when your network can't function without reliable NTP infrastructure. If your devices have wrong time that means no service for end-user. That's bad, isn't it? :)

I can name at least four technologies which comes to mind when we talk about NTP vital dependency:

I was always curious how the IPSec session looks like after PAT translation. As we discovered in IPSec basics: IPSec through NAT article, IPSec must use some NAT-avoiding mechanism to work through NAT/PAT. I have to say (for those who aren't IPSec fan) that most IPSec connections are made through the NAT (at least most Remote Access VPN connections). So that is a common case when IPSec session encapsulated in udp packets (in case of NAT-T).

Let's see what happens with one (first) IPSec session before and after PAT.