Consider the following configuration where an iPad is used to tunnel into a factory to access a temperature sensor:
T <iPad> U | (3G or WIFI) N <internet> N | (DSL) E F <modem> L A | (ethernet) | C <Cisco ASA> T | (ethernet) O <temperature sensor> <-- fixed IP R Y
The main purpose of tunneling into the temperature sensor (and a few other devices) is for a remote worker to determine what needs to be done in the case of a power outage. The processes are fine without power for a few hours, but if the temperature of certain things drops too much, someone needs to go there to sort things out. The modem, ASA, and temperature controllers, etc all have battery backup easily lasting several days.
Most of the ASA VPN configurations I have read about include a DNS server. There are also some vague mentions of connectivity issues when using IPs as compared with FQDNs. Note that there is no DNS server at the factory (particularly not during a power outage).
My questions are as follows:
1. Is it possible to establish a VPN connection with a DNS-less LAN at all?
2. Is it possible to do so from iOS?
3. Are there VPN pitfalls I should be aware of that result from not having a DNS server on the LAN?
4. Is there some other way to do name resolution without a power consuming server?